Fast 800 Keto: Eat well, burn fat, manage your weight long-term

Overall score

Scientific accuracy

Reference accuracy

Healthfulness

How hard would it be to apply the book's advice? Very difficult

Book published in 2021

Published by Short Books

First Edition, Paperback

Review posted May 4, 2023

Primary reviewer: Samuel Dicken

Peer reviewer: Seth Yoder

Table of contents

1. Introduction
2. Scientific accuracy
3. Reference accuracy
4. Healthfulness
5. Most unusual claim
6. Other
7. Conclusion
8. Updates

Claim 1

A calorie restricted, low carbohydrate, ketogenic diet is the most effective diet for rapid weight loss.

Supporting quote(s) and page number(s)

Page 10: “Ketogenic diets promise rapid fat loss and – as a bonus – going keto should stop you from feeling hungry”

Page 10: “a keto diet can work really well at suppressing appetite and helping people lose weight”

Page 11: “Most standard keto diets are not calorie restricted, but as I will show you, a short-term low-calorie keto diet, particularly one where you add an element of intermittent fasting, can be very effective for rapid weight loss and restoring health”

Page 11: “Once they had gone into ketosis they weren’t tormented by hunger pangs and they not only lost significant amounts of weight – fast – but they also saw big improvements in their blood sugar levels, blood pressure, mood and overall energy.”

Page 67: “A number of studies have shown that when you go into ketosis you feel less hungry, lose weight and shed body fat.”

Page 68: “If you want to lose weight and improve your metabolic health, then, based on lots of studies, I think the best thing you can do is go on a low-calorie keto diet for a limited period to kick-start rapid weight loss”

Page 69: “Most keto diets don’t restrict calories, but my plan does because studies show this is the most effective way to get into ketosis and lose weight, fast.”

Page 76: “The Fast 800 Keto diet is a great way to start your weight loss journey, because you swiftly go into ketosis, and when that happens you start to burn fat, fast.”

Page 77: “The first and most impactful part of the plan is the keto phase, and it’s also the simplest.” … “The combination of low calorie and low carb will ensure that you very rapidly move into ketosis – where you start using your stores of body fat as your main energy source.”

Page 86: “Although most people will be turning to the Fast 800 Keto to lose weight fast – and this is the best possible way to do that!”

Criterion 1.1. How well is the claim supported by current evidence?

2 out of 4

Fast 800 Keto argues that a calorie restricted, low-carbohydrate, ketogenic diet is the most effective diet for achieving rapid weight loss. This is suggested to be because a ketogenic diet “flips the metabolic switch”, to promote fat burning and lead to significant weight loss. A ketogenic diet is also proposed to make weight loss easier, by reducing appetite and feelings of hunger. The book therefore recommends a ketogenic diet at 800-900 calories per day for up to 12 weeks, to achieve rapid weight loss. The book repeatedly states the importance and value of being in ketosis for weight loss. This claim is weakly supported, with evidence to date indicating that weight loss scales with the extent of the calorie deficit, regardless of macronutrient content. Any low calorie diet produces rapid weight loss, regardless of macronutrient content.

When consuming a very low amount of carbohydrates for several days, the body starts to switch to using fats for energy, converting them into ketone bodies. This is called ketosis. The Fast 800 Keto proposes that being in ketosis during a low calorie diet is important to burn fat, to help reduce appetite and preserve resting metabolic rate during weight loss. The beneficial mechanisms of a ketogenic diet might suggest that a ketogenic diet could be superior to other diets for weight loss. However, evidence weakly supports this claim.

Low calorie diets containing 800 kcal per day generally result in greater weight loss than standard weight loss diets with moderate restriction (a 500-750 calorie deficit, which produce around 5-8% weight loss at 6-12 months). For example, in the DiRECT study, a 12-week low calorie diet (extendable to 5 months if participants wished) led to 15 kg of weight loss at 12 months, and sustained weight loss compared to usual care at 24 months. In the DROPLET trial, a 12-week low calorie diet resulted in 10.7 kg weight loss at 12 months. These trials showing the effectiveness of low calorie diets for weight loss are similar to the diet proposed in Fast 800 Keto, with a 3-month 800-900 calorie diet. The key difference however, is that the Fast 800 Keto claims that for best outcomes, the low calorie diet should be a ketogenic diet. At no point does the book suggest that any low calorie diet would be as effective as a low-carbohydrate, ketogenic low calorie diet for weight loss. But, low calorie diets with different macronutrient content result in similar amounts of weight loss. Macronutrient composition does not appear to influence weight loss. In fact, the strongest evidence for large and rapid weight loss comes from trials that use high-carbohydrate, low calorie diets, with limited evidence for low calorie, ketogenic diets for weight loss. The DiRECT study above used a total diet replacement providing 825-853 kcal per day, consisting of 59% carbohydrate, 13% fat and 26% protein. Similarly, the PREVIEW trial provided 810 kcal per day, consisting of 43.7% protein, 41.2% carbohydrate and 15.1% fat, and participants achieved 10-11% weight loss after 8 weeks. And, the DIADEM-I trial provided 800-820 kcal per day from a total diet replacement consisting of 57% carbohydrate, 14% fat, and 26% protein for 12 weeks. Participants in the intervention group lost 11.98 kg in 12 months. Therefore, there is no apparent weight loss advantage from a low-carbohydrate, ketogenic 800 calorie diet over other 800 calorie diets.

Ketogenic diets do not provide a weight loss advantage at low calorie intakes. In fact, at any level of consciously controlled calorie intake, evidence weakly supports a superior weight loss benefit from a ketogenic diet. With moderate calorie restriction, calorie-matched ketogenic and non-ketogenic diets result in similar weight loss. In one metabolic ward study, a 6-week ketogenic diet- and a 6-week non-ketogenic, low-carbohydrate diet matched for protein and calories at 1500 kcal per day resulted in the same weight loss after 6 weeks. There were also no differences in hunger ratings or resting energy expenditure between the groups at 6 weeks. Similar results are seen when comparing weight loss on calorie matched ketogenic and non-ketogenic diets in free-living studies. A randomized controlled trial compared a very-low carbohydrate diet with a 500-1000 calorie deficit to a calorie-matched high-carbohydrate diet, for 1 year. Both diet groups lost large amounts of weight, with no significant difference between groups. At 2 years, there was still no difference in weight loss. Similar weight loss is seen in other trials that compare calorie-matched ketogenic and non-ketogenic diets, with a modest 30% calorie deficit.

A ketogenic diet does at least appear to result in weight loss, which Fast 800 Keto can be credited for. When calorie intake is not consciously controlled, a number of trials show that adhering to a ketogenic diet can lead to weight loss at 3-6 months. This benefit is also seen in the target population of Fast 800 Keto. Meta-analyses of randomized controlled trials show that people living with overweight or obesity, with or without type 2 diabetes, lose weight when they adhere to a ketogenic diet. When comparing a calorie unrestricted low-carbohydrate ketogenic diet with a calorie unrestricted low-fat diet, there tends to be slightly greater weight loss with a ketogenic diet at 3-6 months. However, by 12 months, there is no significant difference in weight loss. As with a low-carbohydrate ketogenic diet, a low-fat diet also restricts food choices, and tends to result in a calorie deficit without controlling energy intake. In fact, weight loss without consciously reducing calorie intake tends to occur across a number of different diets. When certain foods are restricted or eliminated from the diet, people tend to consume less energy than they expend. However, this is not always the case. A metabolic ward study showed that a 2-week calorie unrestricted ketogenic diet resulted in weight gain, whereas a 2-week calorie unrestricted high-carbohydrate diet resulted in weight loss.

The Fast 800 Keto provides several references to support its claim of a low calorie ketogenic diet as being most effective for weight loss. But, these are studies of very-low-calorie, ketogenic diets providing 800 kcal per day, not low-calorie ketogenic diets providing 800-1200 kcal per day. Most of the references include observational studies, or non-randomized trials. For example, this systematic review and meta-analysis of very-low-calorie, ketogenic diets was cited. It consists exclusively of very-low-calorie keto diets, which is not the same diet that Fast 800 Keto proposes. In fact, Fast 800 Keto points out that there are “key differences” between very-low-calorie, ketogenic diets as in these trials, and the diet proposed in the book,  such as the higher calorie content of the proposed diet. Additionally, this 2001 meta-analysis showing that very-low-calorie diets had greater initial weight loss and maintained significantly more weight loss at 5 years than a moderately calorie restricted, balanced diet does not support the superior weight loss claim of a ketogenic diet. Fast 800 Keto also cites a randomized controlled trial comparing a very-low-calorie, ketogenic diet with a standard low-calorie diet, which again supports a large calorie deficit for greater weight loss, but not that the ketogenic aspect was crucial. The book does include the DiRECT study mentioned earlier in the reference list. However, it has been incorrectly referenced. Where the reference is cited in the book, it discusses a different DIRECT study regarding low-carbohydrate, low-fat and Mediterranean diets. Therefore, the book does not actually provide direct evidence for the effectiveness of its proposed low calorie, ketogenic diet being superior to a low calorie non-ketogenic diet, or ketogenic diets per se being superior to non-ketogenic diets for weight loss.

What about the proposed beneficial mechanisms of a ketogenic diet on satiety and metabolic rate? Adhering to a ketogenic diet for a few weeks does tend to be associated with reduced subjective ratings of hunger and appetite. Circulating levels of the hunger hormone, ghrelin, typically rises with weight loss, but may potentially be suppressed in ketosis. Regarding energy expenditure, metabolic rate slowswith weight loss to a greater extent than is expected based on changes in fat mass and fat-free mass alone. However, this slowing is not meaningfully influenced by macronutrient content, with at best, a small increase in energy expenditure with carbohydrate restriction. A meta-analysis of 29 controlled feeding studies showed that adhering to a low-carbohydrate diet may increase total energy expenditure (which includes resting metabolic rate, the energy required to eat and digest food, and the energy expended from exercise and non-exercise activity) after 2 ½ weeks, following an initial decrease. However, the size and importance of this change in energy expenditure for weight management is debated. Another systematic review and meta-analysis of tightly controlled feeding studies showed no meaningful difference in total energy expenditure, nor weight loss, with different amounts of carbohydrate (from 1% to 83%) or fat content (4% to 84%). In fact, the analysis slightly favored lower-fat diets. A number of other trials also show no meaningful difference in resting metabolic rate or total energy expenditure between diets with different carbohydrate intakes, such as a re-analysis of this randomized controlled trial based on the original pre-registered analysis plan, this randomized controlled trial, and this metabolic ward study. Even if differences in metabolic rates exist between diets, preserving metabolic rate is not necessarily beneficial for weight loss outcomes. After an intense diet and exercise weight loss programme, those with the greatest weight loss were also those with the greatest slowing of resting metabolic rate; metabolic adaptation scaled with the extent of weight loss. At 6 years follow-up, those with the greatest slowing of resting metabolic rate were also those with the greatest weight loss, and the extent of metabolic adaptation was not associated with weight regain.

Health organization guidelines state that for weight loss, an energy deficit is required. The extent of weight loss then scales with the size of the deficit. A systematic review and meta-analysis showed that very-low-calorie diets and low calorie diets tend to produce similar amounts of weight loss, but these are greater than weight loss from diets with moderate calorie restriction. An umbrella review of diets for weight loss and type 2 diabetes remission showed that very-low-calorie diets produce greater weight loss than moderately calorie restricted diets, regardless of macronutrient intake. For example, participants randomized to a very-low-calorie ketogenic diet lost more weight at all time points over 24 months than a typical calorie restricted diet providing 1400-1800 kcal per day, from the larger calorie deficit. Obesity Canada’s medical nutrition therapy guidelines highlight that there is no meaningful difference in weight loss between different calorie unrestricted diets. And when calorie intake is restricted, the need to be in ketosis is not important, nor superior. A scientific statement from the National Lipid Association in 2019 reviewing the evidence for low-carbohydrate and very-low carbohydrate/ketogenic diets for body weight and cardiometabolic risk factors concluded that: “Low- and very-low-carbohydrate diets are not superior to other weight loss diets.”.

In summary, the claim of superior weight loss with a low carbohydrate, ketogenic diet whilst on a low calorie diet is weakly supported. Short-term, low calorie diets with a range of macronutrient proportions have strong evidence that they all result in rapid and large weight loss. A very-low carbohydrate, ketogenic low calorie diet may be suitable for some individuals, but is not superior to any other low calorie diet for weight loss. Whilst some of the favorable mechanisms from a ketogenic diet have been shown, these have not resulted in greater weight loss in trials that compare calorie-uncontrolled ketogenic diets with calorie-uncontrolled non-ketogenic diets, or calorie-controlled ketogenic diets with calorie-matched, calorie-controlled non-ketogenic diets. The Fast 800 Keto appears to take the potential mechanistic benefits of a calorie unrestricted, ketogenic diet for weight loss and apply them to a calorie-restricted, low calorie diet. This claim is like saying an 800 calorie, low-fat diet is better for weight loss than a conventional, moderately calorie-restricted low-fat diet because of the low-fat aspect. It is, but the low-fat component is largely irrelevant, the greater calorie deficit is what is important.

Of note, a number of systematic reviews and meta-analyses on the topic combine trials that compare ketogenic diets that are calorie uncontrolled or calorie controlled with varying levels of restriction, with a range of comparator diets with varying macronutrient content and/or calorie content. This makes it difficult to separate the effect of macronutrient content with that of greater calorie restriction. It is also unclear to what extent individuals need to restrict carbohydrates to enter ketosis, and what level of ketosis is needed to suppress appetite.

 

Criterion 1.2. Are the references cited in the book to support the claim convincing?

 

Criterion 1.3. How well does the strength of the claim line up with the strength of the evidence?

2 out of 4

 

Overall (average) score for claim 1

2 out of 4

Claim 2

Low-protein ultra-processed food drives hunger and is the primary cause of  energy overconsumption and obesity, and high protein diets reduce hunger, appetite and energy intake.

Supporting quote(s) and page number(s)

Page 12: “It is also important, during every stage of this diet, to keep eating plenty of protein, well above current recommended levels. Extra protein, combined with some easy-to-do exercise which I describe in Chapter 7, will not only help reduce your appetite and cravings, but ensure that you preserve your muscle mass as you lose weight, fast.”

Page 13: “You will read far more about the importance of protein, and the major role that lack of good-quality protein has played in our obesity epidemic, in Chapter 2.”

Page 45: “Another possible explanation for why people ate more on the ultra-processed food diet – which Dr Hall plans to test in future experiments – is that, although the meals were matched for carbs and fat, they were not precisely matched for protein. Fourteen per cent of the calories in the ultra-processed foods were made up of protein, versus 15.6% of the calories in the healthier meals… The difference appears small, but Dr Hall thinks it may, nonetheless, have contributed to the very different outcomes.”

Page 49: “‘the Protein Leverage Hypothesis’, which argues that we have a specific appetite for protein and that the relatively low levels of protein in ultra-processed foods have been one of the major drivers behind the current obesity epidemic. This theory is currently gathering a lot of fans (including me).”

Page 49: “we don’t just have one appetite, for food in general, we actually have five: one each for protein, fat, carbs, calcium and salt… But it is the need for protein that dominates the others.”

Page 46: “ultra-processed foods tend to be low in protein, and as we are about to discover, protein is a key driver of appetite.”

Page 50: Protein Leverage: “That’s why it’s so easy for some of us to polish off a big bag of crisps or a packet of biscuits in one sitting.”

Page 53: “A key claim of the Protein Leverage Hypothesis is that to satisfy our protein hunger, most of us need to get around 15-20% of our calories in the form of protein.”

Page 54: “Tragically, people with metabolic disease, like Type 2 diabetes, are still being told to eat a low-protein, high-carbohydrate diet, which puts them at much greater risk of obesity and ill-health.”

Page 60: “Eating adequate amounts of good-quality protein is vital for keeping you strong and slim.”

Page 60: “We have a powerful appetite for protein, and if you aren’t getting enough, or if it is being ‘diluted’ by lots of fat and carbs (so that the percentage of protein in your diet dips below 15%), you will find that you are often hungry.”

Page 60: “One of the tricks that the producers of ultra-processed foods play on us is adding flavours that fool our taste buds into thinking they are eating something that is protein-rich, when it is not. That is one of the reasons we go on eating more and more of these foods, in a desperate search for protein that is not there.”

Criterion 1.1. How well is the claim supported by current evidence?

3 out of 4

This claim scored 3, indicating that it is moderately supported by current evidence.

Obesity is a global health problem, with the prevalence increasing massively in the past 40 years. There is general consensus that obesity is the result of a long-term imbalance between energy intake and expenditure, particularly from an increase in energy intake. However, what drives this imbalance is debated. The Fast 800 Keto argues that the primary cause of increased energy intake is from the low protein content of foods now commonly consumed worldwide.

Mounting evidence shows that shifts in the food environment towards greater ultra-processed food intake has resulted in increased energy intake. Diets high in ultra-processed food are associated with increased risks of weight gain and obesity in large observational studies, and in a tightly controlled experimental trial. However, what it is about ultra-processed food that leads to increased energy intake is debated.

Several models exist that try to explain what causes obesity, and why obesity rates have rapidly increased recently. One model is the Protein Leverage Hypothesis. The Protein Leverage Hypothesis argues that the body seeks a certain amount of protein in the diet. When our food is low in protein (i.e. ‘protein-diluted’ food), the drive to consume enough protein would mean consuming more food until enough protein is consumed. This means that an appetite for protein when consuming low-protein food will lead to greater energy intake. This could make sense, as across different populations in multiple countries including the US, protein intake is relatively constant at 16%, irrespective of sociodemographics or lifestyle factors. Also, ultra-processed foods tend to be lower in protein. And, as the proportion of total energy obtained from ultra-processed food increases, total energy intake also increases.

If protein leverage was driving increased energy intake and obesity, then we would expect low-protein diets (as a proportion of total energy) to be associated with a higher energy intake, and high-protein diets (as a proportion of total energy) to be associated with lower energy intake. Across low-, medium- and high-protein diets (as a proportion of total energy), absolute protein intake should then be relatively similar.

Evidence from observational studies supports that the protein leverage hypothesis may explain the rising prevalence of obesity. In the US, the amount of protein in the food supply as a percent of total energy did not appear to significantly change in the past 40 years, whilst obesity rates increased. However, the amount of protein in the total food supply did actually fall by around 1%. Modeling the influence of protein leverage on energy intake with this drop in protein content, partial protein leverage could explain about a third of the observed weight gain in the US obesity epidemic, with perfect protein leverage explaining around two thirds of the observed weight gain. However, this analysis relied on total food supplies from food balance sheets, which represent the national food supply, rather than what people actually consumed.

Results from the Australian national dietary survey suggested that the protein supply was diluted from 1983 to 1995 (a decrease from 17.7% to 16.8% of total energy), potentially leading to increased energy intake during this period. However, the proportion of protein subsequently increased from 1995 to 2012, and rates of obesity still continued to rise. Another analysis of the Australian national dietary survey also reported that energy intake was inversely related to the proportion of protein in the diet. There were also changes in the amount of protein consumed later in the day depending on how much protein was consumed at the start of the day. People with a higher protein intake at the start of the day consumed less protein later on, and people with a lower protein intake at the start of the day consumed more protein later on. However, this compensation was incomplete, or partial. People with a lower morning protein intake didn’t make up the difference later on, consuming more energy and less protein across the day than people with a higher morning protein intake. Of note, some studies analyse the dry weight of foods, not wet weight, which is how food is usually consumed. In the US, similar findings were found. Diets high in ultra-processed food had a lower protein content as a proportion of total energy, and were also associated with higher energy intake. Absolute protein intake was therefore constant across people, as the protein leverage hypothesis would predict. However, these observational designs cannot draw causality, and protein may not be the primary factor. The increased energy intake might be driven by the greater energy density and hyper-palatability of ultra-processed food with combinations of fat, salt and sugar.

What about in trials where people are given food? If protein leverage was driving increased energy intake and obesity, then giving people a low-protein diet (i.e. ‘protein-diluted’ food) should increase their energy intake and lead to weight gain, and giving people a high-protein diet (i.e. ‘protein-rich food) should decrease their energy intake, and lead to weight loss. In both diets, there should be a similar absolute amount of protein intake.

In a meta-analysis of 38 trials where people were given calorie uncontrolled diets with varying macronutrient content, a higher proportion of energy from protein was associated with a lower energy intake. Energy intake from non-protein sources increased as the percentage of energy intake from protein decreased. A metabolic ward study, where energy intake and expenditure are closely monitored, compared a 2-week ultra-processed diet with a 2-week minimally processed diet. After 2 weeks on the ultra-processed diet, people gained 0.9 kg of weight, whereas they lost 0.9 kg on the minimally processed diet. There was a small, non-significant, but potentially important difference in protein between the diets (14% of total energy on the ultra-processed diet, versus 15.6% on the minimally processed diet). In modeling analyses, the protein leverage hypothesis could explain around 50% of the differences in energy intake. Protein could therefore be an important factor driving energy intake, but it is unlikely to be the sole factor. However, the metabolic ward study and trials in the meta-analysis were not designed to test the protein leverage hypothesis.

A number of trials have attempted to directly assess the protein leverage hypothesis. In one controlled feeding trial, participants had access to a vending machine with foods containing varying amounts of protein. The study found that greater morning protein intake was associated with lower energy and protein intake later in the day. However over several days, there was a stable macronutrient pattern, with similar proportions of protein, carbohydrate, and fat intake. Other studies show a compensatory effect after a short-term, low-protein diet, with greater energy intake than a short-term, high-protein diet.

Other controlled feeding studies suggest that protein leverage may be partial or incomplete (there is some influence of protein content on energy intake, but changes in energy intake do not completely balance absolute protein intake, as the protein leverage hypothesis would predict). Some studies suggest that energy intake does not increase with a low-protein intake. For example, in two randomized crossover studies, participants received three 12-day diets containing 5%, 15%, and 30% protein. The 30% protein diet led to reductions in energy intake, but there was no difference in energy intake between 5% and 15% protein diets. The lack of increased energy intake with the 5% diet led to a decrease in absolute protein intake. And, despite a reduction in energy intake at 30% protein intake, there was still an absolute increase in protein intake. It has been suggested that the 5% protein diet does not represent typical diets in populations with adequate food supplies, which may explain the lack of an effect. Other studies instead suggest that a high-protein intake does not decrease energy intake. A metabolic ward study provided three 4-day diets with 10%, 15%, and 25% protein. There was a higher energy intake on the 10% protein diet compared with the 15% protein diet, but there was no decrease in energy intake on the 25% protein diet compared with the 15% protein diet. Absolute protein intake was therefore not constant across the three levels of protein. These studies moderately support the claim made in Fast 800 Keto.

There is also evidence that does not support the protein leverage hypothesis. A secondary analysis of 2,733 in-patient meals from two controlled feeding trials (including the 2019 metabolic ward study above and the low-fat vs. low-carb diet metabolic ward study from claim 1) showed that higher protein intake as a percentage of total energy was predictive of greater energy intake in calorie unrestricted minimally processed or ultra-processed meals, but not predictive of energy intake in calorie unrestricted low-fat or low-carbohydrate meals. Interestingly, greater protein intake at a previous meal was associated with greater energy intake at a subsequent low-fat or low-carbohydrate meal, but was associated with decreased energy intake at a subsequent ultra-processed meal and not associated with energy intake at a subsequent minimally processed meal. Again, these trials were not specifically designed to test the protein leverage hypothesis.

The Fast 800 Keto provides several references to support the claim that low-protein diets increase energy intake and lead to obesity due to protein leverage. But, a number of these references are not peer-reviewed studies from academic journals or publications by credible sources. Only some of the references provided by Fast 800 Keto were considered to be credible sources of primary evidence, including the modeling study, metabolic ward trial and randomized controlled trial mentioned earlier.

Given that a low-protein diet is suggested to increase energy intake, the Fast 800 Keto recommends a higher-protein diet to reduce appetite and hunger, to help keep us “slim”. There is evidence to suggest that a slightly higher protein intake does seem to have a modest effect on increasing satiety. Meta-analyses of short term feeding trials suggest that a higher-protein meal has a modest satiety effect and leads to greater feelings of fullness. In one study comparing 14%, 25%, and 50% of energy from protein, a greater protein intake dose-dependently increased some appetite-suppressing gut hormones, and led to greater satiety.

However, the benefit of a higher protein intake on energy intake and weight loss is less clear, with a limited impact on reducing subsequent energy intake. Shorter-term trials lasting less than a year suggest a benefit of a higher-protein diet versus a lower-protein diet for weight loss, but longer-term studies fail to find a superior benefit of high-protein diets for weight loss. High-protein diets do not seem to provide significantly greater weight loss than standard-protein diets, with general weight loss recommendations based on achieving a calorie deficit, regardless of macronutrient content. The Fast 800 Keto provides a number of references to support its claim of a higher protein intake being beneficial, such as this summary of a meeting of over 60 nutrition researchers to discuss the role of protein for health. However, the reference provides little detail in relation to the claim. Other references are unrelated to the book’s target audience of people with obesity or type 2 diabetes. These references focus on protein requirements during pregnancy, in aging, and to promote muscle strength. Given that the book provides an extreme weight loss diet that is unsuitable for many individuals including pregnant females and the elderly, it is unclear why these references were included in the book and considered relevant.

In summary, the protein content of the diet may influence energy intake, but this response appears to be incomplete, such that the protein leverage hypothesis likely only partially explains differences in energy intake and the obesity epidemic. Most studies supporting the protein leverage hypothesis are based on modeling of observational data, or from re-analysis of calorie-uncontrolled diet interventions that were not testing the protein leverage hypothesis. A small number of controlled feeding trials have tested the protein leverage hypothesis. These trials suggest partial protein leverage, but are generally short-term and may not reflect long-term weight change from protein content. In addition, some controlled feeding trials do not support or even contradict the protein leverage hypothesis. Higher-protein intakes may decrease appetite and increase satiety, but it is currently unclear as to what extent this leads to a subsequently lower energy intake and weight loss.

Criterion 1.2. Are the references cited in the book to support the claim convincing?

3 out of 4

 

Criterion 1.3. How well does the strength of the claim line up with the strength of the evidence?

2 out of 4

Overall (average) score for claim 2

3 out of 4

Claim 3

A lowish-carbohydrate, Mediterranean diet is the most effective diet for weight loss maintenance and preventing weight regain.

Supporting quote(s) and page number(s)

Page 92: “I would suggest that you move on to a relatively low-carb, high-protein Med-style diet, which is the most effective way not only to keep the weight off long-term,…”

Page 93: “Research shows that if you stick to a lowish-carb Med-style diet… you can stop counting calories and will not regain the weight you have so diligently lost.”

Page 93: “by sticking to a healthy Med-style diet, and doing the odd fasting day to compensate if I have overindulged or I feel my trousers pinching, I manage to keep my weight, waist, blood sugars and blood pressure down, without calorie counting.”

Page 130: “There is abundant evidence that the Med diet is a fantastic way of keeping your body and brain in good shape”

Criterion 1.1. How well is the claim supported by current evidence?

2 out of 4

This claim received a score of 2, indicating that it is weakly supported by current evidence.

The Fast 800 Keto claims that a lowish-carbohydrate Mediterranean diet is the best diet for maintaining weight loss and preventing weight regain. After following a low calorie ketogenic diet and a period of intermittent fasting to achieve the desired amount of weight loss, the book recommends a lowish-carbohydrate Mediterranean diet to maintain the weight loss. However, no randomized controlled trials to date directly compare a Mediterranean Diet with another diet following a run-in weight loss period to demonstrate the effectiveness of a Med diet for weight loss maintenance.

Diets can be defined by their macronutrient content (e.g., high-fat or low-fat diets) or by the food groups they include or exclude. For example, vegan, pescetarian or Mediterranean diets are defined by food groups, rather than by macronutrients. A Mediterranean diet is typically rich in plant-based foods such as fruit, vegetables, nuts, legumes, olive oil and wholegrain cereals, with moderate fish intake and minimal sugar-sweetened beverage, dairy or processed red meat consumption. However, there are several definitions of a Mediterranean diet, which all slightly differ. The food groups that are encouraged or avoided in a Mediterranean diet are similar to the food groups that are encouraged or avoided in dietary guidelines, but with slightly different servings per day or week. The Fast 800 Keto emphasizes a “lowish carbohydrate” Mediterranean diet. The book provides no definition as to what defines “lowish carbohydrate”, although a Mediterranean diet containing 41-43% carbohydrate is mentioned. As the Mediterranean diet is defined by the food groups consumed, there is actually no consensus on the carbohydrate content of the diet, which varies greatly with region. In one analysis, carbohydrate content in Mediterranean diets averaged 43%, ranging from 39.6% to 48%, while some studies reported up to 58% carbohydrate content. A recent network meta-analysis defined a Mediterranean diet pattern as containing moderate macronutrient content, with 55-60% of energy from carbohydrates, 15% from protein, and 21-30% from fat.

In general, diet interventions lead to 5-8% weight loss after 6-12 months. But, for most people who go on a weight loss diet, even if they achieve large weight loss, some of the weight is slowly regained over time. Therefore, the issue is less about how to lose weight, and more about how to keep off the lost weight. Because of this, there is interest in finding which diets are effective in maintaining weight loss (i.e., diets that do not lead to weight regain). This highlights the important distinction between weight loss, and weight loss maintenance. Weight loss refers to intentional weight reduction, whereas weight loss maintenance is intentionally losing 10% of initial body weight and keeping it off for at least 1 year. Although, other definitions of weight loss maintenance exist. Diets that may be very effective for weight loss may be unsuitable for weight loss maintenance (e.g. a very-low-calorie diet). And diets that are effective for weight loss maintenance may not be that effective for weight loss.

First, are Mediterranean diets at least associated with improved weight management or weight loss? Yes, in prospective cohort studies, greater adherence to a Mediterranean diet pattern is associated with lower risks of weight gain and developing overweight or obesity. In systematic reviews of randomized controlled trials, a Mediterranean diet tends to result in weight loss, and not lead to weight gain, much like any other weight loss diet. In general, a range of diets including the Mediterranean diet result in similar weight loss at 12 months. Where typically, weight loss is greatest at 3-6 months, with slow weight regain after.

Importantly, Fast 800 Keto recommends the lowish-carbohydrate Mediterranean diet for weight loss maintenance, not weight loss. This is after the first two stages of the Fast 800 Keto diet. Therefore, we need to consider studies that compare different diets after a period of standardized weight loss, where people all receive the same weight loss diet. Some randomised controlled trials compare different calorie unrestricted diets with varying macronutrient content for weight loss maintenance after a run-in low calorie diet for weight loss. But none of these trials for weight loss maintenance look at the Mediterranean diet. In general, these studies find little difference between diets containing different food groups for weight loss maintenance or preventing weight regain, or between high- or low-carbohydrate diets.

In one study, 200 females who had lost 5% or more of their initial body weight were randomized to receive one of two diets for weight loss maintenance. One diet was high in monounsaturated fat, while the other diet was high in carbohydrate. 174 participants were followed up after 2 years, where there was no difference in weight loss between the two diets. These diets contained similar food groups as the Mediterranean diet, with plenty of fruit and vegetables, as well as moderate intakes of nuts, olive oil, fish and dairy on the monounsaturated fat diet, and wholegrains on the high-carbohydrate diet.

Another randomized trial compared three 6-month diets for weight loss maintenance, after an 8-week low calorie diet. The first diet was based on the Healthy Eating Pyramid with moderate fat and high monounsaturated fat content, the second on the US Department of Agriculture Food Pyramid that was lower in fat, and the third was a control ‘Western’ diet. All food was provided for free to participants in a ‘supermarket’. The diets varied in terms of both amounts and types of fat, carbohydrate and protein content, and energy density. All groups lost a similar amount of weight on the low calorie diet, around 12-13 kg. Six months after beginning one of the weight loss maintenance diets, all three groups regained some weight, but with no significant difference between the three diets. By 18 months, there was still no significant difference in weight regain between the three diets. The two intervention diets contained similar food groups as a Mediterranean diet. For example, the Healthy Eating Pyramid diet encouraged eating plenty of nuts, pulses, fruit, vegetables, wholegrain cereals, and vegetable oils including olive oil, as well as moderate intakes of fish, poultry and eggs, and restricted red meat, dairy, sweets and refined carbohydrates. The low-fat USDA diet also favored fruits, vegetables and moderate intake of nuts, pulses, fish, dairy and meat, and restricted sweets and soft drinks. Yet these diets were no better at minimizing weight regain than a control diet which included more added sugar, higher saturated fat, plenty of dairy and red meat, moderate intakes of sweets and soft drinks, and restricted the intake of pulses, nuts and olive oil. Again, these diets were not designed to be a Mediterranean diet, although high monounsaturated fat content is typical of a Mediterranean diet. So, whether a Mediterranean diet pattern per se would have resulted in superior weight loss at 18 months is unclear.

Some studies favor a higher vs. lower protein intake to minimize weight regain after weight loss when calorie intake is uncontrolled. One study found less weight regain after 6 months with an 18% protein diet compared with a 15% protein diet after a 4-week very-low calorie diet. Other trials find no benefit of a higher protein intake for weight regain, but this is when energy intake is tightly controlled and matched during weight maintenance.

The Fast 800 Keto provided no references to support its claim that a lowish-carbohydrate Mediterranean diet is the most effective diet for weight loss maintenance. One study mentioned in Fast 800 Keto was a randomized controlled trial comparing long-term weight loss on a Mediterranean diet versus a low-fat or low-carbohydrate diet in 322 adults. But, it was not actually referenced and instead was erroneously referenced as a different DIRECT study.

Given the lack of randomised controlled trials assessing diets for weight loss maintenance, is there any wider evidence that may support a Mediterranean diet for weight loss maintenance? One retrospective analysis reported that two weight maintenance periods with a Mediterranean diet between and after two short-term, low-carbohydrate, ketogenic weight loss diets helped to minimize weight regain. However, the Mediterranean diets were calorie restricted and not low-carbohydrate, being 58% carbohydrate. There was also no control group, which is needed to assess whether the Mediterranean weight maintenance diet was superior to another diet. In a cross-sectional observational study, greater adherence to a Mediterranean diet after weight loss was associated with a greater likelihood of weight loss maintenance. But this does not indicate whether adherence to a Mediterranean diet is superior to another similar, plant-based diet for weight loss maintenance. Beyond the Mediterranean diet itself, a systematic review found that the strongest dietary determinants for weight loss maintenance are portion control, energy restriction, decreasing energy intake, and cutting out unhealthy foods (e.g. sweet and junk food). This includes an increase in healthy eating, increase in fruit and vegetable intake, and reducing sugar-sweetened beverage consumption. Increased fish or wholegrain consumption had moderate evidence for no significant effect on weight loss maintenance. In a secondary analysis of two studies, weight loss maintainers consumed diets with a lower energy density, and with greater consumption of fruit and vegetables, wholegrains, and more fiber than individuals with overweight or normal weight. When looking at weight loss registries, a low-fat diet tends to be common in successful weight loss maintainers. Although, weight loss registries may not reflect the general population. In general, these analyses consider the food groups or nutrient content of diets and their relation with long-term weight loss maintenance, from studies where the diets were used to achieve weight loss itself.

In summary, maintaining weight loss is difficult. Most people regain some weight after weight loss, regardless of what diet they follow. Therefore, the claim by Fast 800 Keto that a low-ish carbohydrate Mediterranean-style diet will result in no weight regainis weakly supported. There is a lack of evidence to support that a Mediterranean diet, particularly a low-ish carbohydrate Mediterranean diet, is superior for weight loss maintenance or for preventing weight regain. There is a lack of evidence to suggest that any single diet pattern is best for weight loss maintenance, as summarized: “well beyond weight loss per se, the maintenance of the lost weight remains the major challenge in weight management and in this area we do not have solid evidence to recommend specific dietary regimens”. A Mediterranean diet is one of many diets that can be used for weight management, with a number of diet patterns producing similar outcomes for weight loss maintenance. These include plant-based diets in general, such as vegetarian diets, the Dietary Approaches to Stop Hypertension (DASH) diet, diets recommended in dietary guidelines and the Mediterranean diet. Components of a Mediterranean diet are associated with weight loss maintenance and reduced risks of weight gain (such as avoiding sugar-sweetened beverages), but these components are also found across a range of other diets. For example, the DASH diet is also rich in vegetables, fruits and low-fat dairy products, with increasing consumption of these food groups associated with maintaining weight loss. A Mediterranean diet can help to manage weight, but so can a number of other diets.

Criterion 1.2. Are the references cited in the book to support the claim convincing?

1 out of 4

 

Criterion 1.3. How well does the strength of the claim line up with the strength of the evidence?

2 out of 4

 

Overall (average) score for claim 3

 

2 out of 4

Overall (average) score for scientific accuracy

2.3 out of 4

Reference 1

Reference

Chapter 5, reference 41. Harvard T.H. Chan School of Public Health webpage

Associated quote(s) and page number(s)

Page 103: “if you have an Asian ethnic background you are far more likely to develop Type 2 diabetes, heart disease or hypertension than someone who identifies as White with the same BMI.”

Criterion 2.1. Does the reference support the claim?

4 out of 4

The reference received a score of 4, indicating that it supports the claim being made.

The reference is a link to a Harvard T.H. Chan School of Public Health webpage. This is not a peer-reviewed journal, but is a highly-respected University website. The page provides a description of ethnic differences in BMI and disease risk with supporting evidence from peer-reviewed academic papers. The reference does support the claim that Asian ethnicities have a higher risk of type 2 diabetes, heart disease or hypertension.

Ideally, the Fast 800 Keto should reference a peer-reviewed paper. It is worth noting that the website is slightly outdated. The most recent reference on the webpage is from 2011, and there have since been changes to recommended BMI cutoffs compared with what is stated on the webpage.

Reference 2

Reference

Chapter 7, reference 46. Chastin et al., Br J Sports Med 55(22):1277-1285, 2021

Associated quote(s) and page number(s)

Page 152: “Fascinating data from six studies, which included more than 130,000 adults in the UK, US and Sweden, used mathematical modelling to determine how different combinations of activities – including moderate-to-vigorous exercise (such as brisk walking, running or other activities that increase heart rate), light physical activity (such as housework or casual walking) and sedentary behaviour – affect mortality.[46]

If you are largely sedentary, punctuating your day with ‘light activity’ is key. According to researchers, the ideal exercise cocktail consists of 12 minutes of light activity or three minutes of moderate-to-vigorous activity for every hour you spend sitting… This could be enough to reduce your risk of early death by 30%.”

Criterion 2.1. Does the reference support the claim?

3 out of 4

This reference received a score of 3, indicating that it offers moderate support for the claim.

This was a study of 130,239 participants across six prospective cohorts from the UK, US and Sweden. The study looked at the amount of time people spent in different activities (physically active, sedentary or sleeping) and the risk of all-cause mortality. Physical activity was measured using activity monitors worn on the hip or wrist. They found that the relationship between daily activity and all-cause mortality is non-linear and complex. The benefit of a certain amount of physical activity depended on how much time was spent being sedentary, or performing other physical activity. For example, the amount of time spent being moderately or vigorously active was associated with a lower risk of all-cause mortality, but this was influenced by the amount of sedentary behavior or light physical activity that someone did. There were a range of different combinations of time in each activity zone that could reduce the risk of all-cause mortality.

The paper did not state that splitting up sedentary behavior with light activity was key, but said that replacing sedentary behavior with light activity or moderate to vigorous activity was important to lower mortality risk, with a shorter duration needed with moderate to vigorous activity. It is unclear where the values of 3 and 12 minutes in Fast 800 Keto were obtained. The authors of the study also did not provide an ‘ideal exercise cocktail’. The study instead provided a range of different options for reducing all-cause mortality depending on how much time was spent in each activity zone. Notably, the study found large variability in the results between hip- or wrist-worn activity monitors, suggesting the results cannot be as precise as Fast 800 Keto describes.

Reference 3

Reference

Chapter 1, reference 18.  Hall et al., 2019 Cell Metab. 30(1):67-77.e3. 

Associated quote(s) and page number(s)

Page 43: “Further direct evidence that ultra-processed foods are behind the rise in obesity comes from an experiment carried out by Dr Kevin Hall, an American researcher who started out as a sceptic. He thought it was very unlikely that ultra-processed foods were as bad as people were claiming, so he decided to do an experiment to find out.”

The study is then described in detail across pages 43 to 45.

Criterion 2.1. Does the reference support the claim?

4 out of 4

This reference received a score of 4, indicating that it offers strong support for the claim. Fast 800 Keto claims that ultra-processed food is driving obesity.

The study is a metabolic ward crossover study comparing an ultra-processed diet with a minimally processed diet. Fast 800 Keto accurately describes the study methods and results, which support the claim. The study found that an ultra-processed diet led to weight gain, but a minimally processed diet matched for presented energy and macronutrients resulted in weight loss.

Reference 4

Reference

Chapter 1, reference 10. Estruch et al., N Engl J Med 378:e34. 2018 

Associated quote(s) and page number(s)

Page 24: “In a really important study called Predimed, 7447 men and women were randomly allocated to either a standard low-fat diet or a higher-fat Mediterranean diet, in which they ate at least three portions of fruit and vegetables a day, plus fish and legumes (pea, lentils, beans) a minimum of three times a week.[10]

…Indeed, this trial was stopped early because those on the higher-fat Med diet were doing so much better than those on the low-fat diet, with 30% fewer heart attacks and strokes.”

Criterion 2.1. Does the reference support the claim?

4 out of 4

This reference received a score of 4, indicating that it offers strong support for the claim. The study cited is the PREDIMED controlled trial, where 7447 men and women were randomly* allocated to either a standard low-fat diet or a higher-fat Mediterranean diet. Technically, there were three groups, two Mediterranean diet groups (given either extra-virgin olive oil or mixed nuts), and a group advised to lower their dietary fat intake. The Mediterranean diet groups were advised to eat at least three portions of fruit and two portions of vegetables a day, plus fish and legumes (pea, lentils, beans) a minimum of three times a week, as well as other recommendations.

The main outcome of interest was a major cardiovascular event (heart attack, stroke, or death from cardiovascular causes). The trial was indeed stopped early in an interim analysis. There was a 31% and 28% lower risk of major cardiovascular events in the two Mediterranean diet groups compared with the control group. The unadjusted risks were 30% for both Mediterranean diet groups compared with the control group, as stated in the book.

The foods mentioned in the claim also align with the differences in the diets. After the intervention, dietary intakes between the groups differed based on the provided extra-virgin olive oil or mixed nuts, as well as from differences in fish and legume intake, but less so on other food groups. Many participants were already consuming a Mediterranean diet at baseline, and the control group were also advised to eat a healthy diet.

*It is worth noting that the reference is the latest version of the study, as the original was withdrawn as it became apparent that not all participants had been randomized to a diet. Therefore, technically not all 7447 participants were randomly allocated. The new publication results have been updated to reflect this.

Reference 5

Reference

Chapter 4, reference 35. University of Surrey webpage

Associated quote(s) and page number(s)

Page 82: “The original TRE studies were on rats, and it took a while for human studies to get going. In fact, I was involved with one of the first human TRE studies, carried out by Dr Jonathon Johnston of the University of Surrey.[35]”.

The study is then described in detail across pages 82 and 83.

Criterion 2.1. Does the reference support the claim?

2 out of 4

This reference received a score of 2, indicating that it offers weak support for the claim. The reference is a link to a University of Surrey press release about the study in question. There is a link to the peer-reviewed study in the sub-heading of the website reference.

The study is a pilot feasibility study looking at a ‘moderate’ amount of time restricted eating (TRE) in humans. Pilot feasibility studies are small in size, and are used to see whether a certain intervention or study design is feasible to adhere to (e.g. looking at whether participants stick to the diet, rather than looking at whether the diet is effective). For example, this study only had 13 participants, and the primary interest was in the recruitment, attrition and feasibility of the TRE diet. Pilot studies are not designed to see whether a certain diet is more effective than another. The results should not be used to inform scientific understanding, but to guide a larger scale study. Therefore, the results of this study should not be used to guide whether TRE may be effective for weight loss or improving health.

The study methods and results were accurately described in the book. One group of participants were told to eat breakfast 90 minutes later than usual, and dinner 90 minutes earlier than usual (the TRE group). The other group were told to eat their meals at their normal times (the control group). It is unclear whether participants were randomized to the TRE or control group. This is important to reduce the risk of bias and differences between the two groups beyond the timing of their meals. After 10 weeks, the TRE group experienced greater fat loss, but there was no significant difference in weight loss compared to the control group. Blood sugar levels significantly changed between the two diets, but mainly from an increase in blood sugar levels on the control diet. Levels of all other biomarkers (total cholesterol, LDL-cholesterol, HDL-cholesterol, insulin and triglycerides) were not significantly different after 10 weeks. The lack of significance may be due to the small sample size, because the study was not designed to find significant differences in the outcomes.

It is also important to note that Fast 800 Keto states: “Everyone kept a food and sleep diary to ensure they were eating the same amount as normal.”. This implies that the results of the study were not due to changes in energy intake, and energy intake was unchanged on both diets. However, the paper clearly outlines that energy intake was significantly reduced on the TRE diet: “Although there were no restrictions on what participants could eat, researchers found that those who changed their mealtimes ate less food overall than the control group.”.Therefore, the statement in Fast 800 Keto does not accurately reflect the study findings.

Reference 6

Reference

Chapter 3, reference 33.  Fothergill et al., 24(8):1612-9. 2016.

Associated quote(s) and page number(s)

Page 74: “smart researchers at the National Institute of Diabetes and Digestive  and Kidney Diseases wanted to see what happened to them in the long term, particularly to their metabolic rate.[33]”

“What they found was that although the contestants had regained most of the weight they’d lost, they had still kept off around 17kg. But the bad news was that since the start of filming, their metabolic rates had fallen dramatically. They were now on average burning 500 calories a day less than you would expect of their weight and physical activity.”

Criterion 2.1. Does the reference support the claim?

4 out of 4

This reference received a score of 4, indicating that it offers strong support for the claim.

The book largely just describes the study design and main findings. The wider claim is in reference to ketogenic diets not resulting in metabolic adaptation/a reduction in metabolic rate.

The study is a 6-year follow-up of 14 out of 16 participants from ‘The Biggest Loser’ TV show. The show involved an intense diet and exercise intervention to produce rapid and large weight loss in a group of individuals living with obesity.

After losing 58.2 kg by the end of the competition, participants had regained a lot of the weight by 6 years, where average weight loss was now 17.3 kg since the start of the TV show. After 6 years, participants had a resting metabolic rate that was 499 kcal lower than what would be expected (called metabolic adaptation). This was calculated as the difference between their predicted and measured resting metabolic rate. However, their predicted resting metabolic rate was not based on their weight and physical activity, as stated in Fast 800 Keto, but based on their fat-free mass, fat mass, age and sex. The baseline measured resting metabolic rates were similar to what would be predicted, so they did not start with an unusually lower resting metabolic rate. The reduction in resting metabolic rate had increased from 275 kcal per day at the end of the 30-week competition, to 499 kcal per day at 6 years.

Reference 7

Reference

Chapter 2, reference 26. Hruby et al., J Gerontol A Biol Sci Med Sci. 75(1): 123–130 2020

Associated quote(s) and page number(s)

Page 57: “Why should you need more protein as you get older? Well, it is mainly because our ageing bodies are not as good at absorbing or making use of protein as they used to be. And too little protein not only leads to muscle shrinkage but also puts you at increased risk of infection and frailness. This seems especially true in women.

In the Framingham Heart Study Offspring, in which 2917 middle-aged men and women were followed for an average of 23 years, they found that women who were eating at least 90g protein a day scored better on measures of frailty, including things like grip strength, being able to go up and down stairs, walk half a mile or dress themselves, than women who were eating 60g of protein a day, or less.[26]”

Criterion 2.1. Does the reference support the claim?

3 out of 4

This reference received a score of 3, indicating that it offers moderate support for the claim. The claim states that people need more protein as they get older, to avoid the risk of infection and frailness.

The reference is an observational study looking at the association between protein intake and physical function with age. 2,917 middle-aged US adults completed a validated food frequency questionnaire (“how often do you eat a portion of food X”?) to ask about their diet. Estimated protein intake from the questionnaire was reasonably similar to more accurate methods. Participants were then followed up for 23 years.

Physical function was assessed using a loss of ‘functional integrity score’ outcome. This was a combination of 17 different measures of function, ranging from daily activities, pushing/pulling objects and heavy work, including those mentioned in the claim. The study did not directly associate protein intake with frailty (which is where there are three or more of: unintentional weight loss, exhaustion/fatigue, low physical activity, slow gait speed and weak hand grip strength). But, the authors did conduct validation analyses to show that a higher functional integrity score was strongly associated with a lower odds of frailty.

People were placed into four equal-sized groups based on their daily protein intake. The lowest group had an average protein intake of 64.4 g, the second lowest 74.4 g, the third lowest 82 g, and the highest group averaging 92.2 g of protein per day. After taking into account a range of other factors that may influence healthy aging (e.g. age, gender, smoking, baseline functional integrity score), the researchers found that a higher daily protein intake was associated with a lower risk of loss of functional integrity over the 23 years of follow-up.

As Fast 800 Keto states, the association was only significant in females, and not in males. Importantly, females with a protein intake of 74.4 g per day (the second lowest group) also had a significantly lower risk of losing functional integrity compared with the lowest group (consuming 64.4 g per day), not just females consuming more than 90 g per day. Females with daily intakes of 82 g also had significantly lower risk in some of the models, but with further adjustment (for other aspects of the diet, socioeconomic factors and having had a cardiovascular event before loss of functional integrity), protein intake was no longer associated with a significantly lower risk. Overall, there was a trend across groups of increasing protein intake for a significantly reduced risk of incident loss of functional integrity.

When looking at relative protein intake across the four groups, the lowest group consumed 0.86 g of protein/kg body weight per day, or 13.5% of total energy. The other three groups consumed 1.01, 1.08 and 1.22 g protein/kg, or 16%, 17.6% and 19.9% of total energy from protein. Given that all three groups had significantly lower risks than the lowest protein intake group, the study more likely suggests that having too low a protein intake is the issue, being associated with a greater risk of loss of functional integrity in females. The study therefore does not necessarily indicate that we should eat ‘more’ protein, such that females need to consume at least 90 g protein per day, and does not support the need for a higher protein intake in males.

The reference does not provide any evidence to support a higher protein intake and a reduced risk of infection, or muscle shrinkage.

Reference 8

Reference

Chapter 2, reference 25. Rizzoli et al., 29(9):1933-1948. 2018

Associated quote(s) and page number(s)

Page 56:“Protein doesn’t just help strengthen and build muscles – it keeps your bones healthy too. According to the International Osteoporosis Foundation, eating more protein (a lot more) ‘is associated with higher bone density, a slower rate of bone loss, and reduced risk of hip fracture, provided that dietary calcium intakes are adequate’. In other words, if you want to keep your bones strong as you get older, you had better increase the protein (and calcium) in your diet.[25]”

Criterion 2.1. Does the reference support the claim?

3 out of 4

This reference received a score of 3, indicating that it offers moderate support for the claim. It is an expert consensus paper by two Osteoporosis organizations, reporting a consensus on the benefits and safety of protein intake for bone health.

The evidence discussed in the consensus report was from systematic reviews and meta-analyses of a range of study designs, including both experimental trials and observational studies at a single point in time, and over time. The review highlights that ‘insufficient’ protein intake is a problem, and suggests that protein intakes at or above the current recommended daily allowance (≥0.8 g/kg bodyweight) reduces bone loss and hip fracture risk. However, the review does not specify how much above the recommended daily allowance is beneficial. It does not define whether this is ‘a lot more’. The review summarizes by saying that there are a lack of well controlled trials to assess dietary protein intake on fracture risk. Fast 800 Keto also does not provide an actual figure for what it considers to be a high protein intake. So, it is unclear how much the review supports the claim. The Fast 800 Keto provides a quote from the review paper to support the claim that protein keeps bones healthy.

Whether people need to consume more protein depends on their current intake. In the UK, older adults (>65) consume on average over 16% of total energy from protein. Protein intake at 0.8 g/kg body weight translates to around 10-15% of total calorie intake as stated in the review. Therefore, it is questionable as to how much greater protein intake should be to ensure protein intake is not insufficiently low, as the review suggests, and whether this current value is what Fast 800 Keto is recommending.

Reference 9

Reference

Chapter 4, reference 38.  Wilson et al., J Strength Cond Res. 34(12):3463-3474. 2020 

Associated quote(s) and page number(s)

Page 89: “Research done with male athletes has shown that, as well as being a stepping-stone from full-on keto to something that is more sustainable long-term, keto cycling leads to more muscle growth, higher levels of testosterone and better performance, when combined with resistance exercises.”

Criterion 2.1. Does the reference support the claim?

2 out of 4

This reference received a score of 2, indicating that it offers weak support for the claim. The claim suggests that keto cycling (in ketosis during the weekdays, and adding more protein and carbohydrate at the weekend to come out of ketosis) leads to more muscle growth, higher levels of testosterone and better performance, when combined with resistance exercises. The reference is a randomized controlled trial of 25 resistance-trained males given a ketogenic diet or a ‘Western diet’ for 10 weeks, who followed a 7-week training programme after 2 weeks of getting used to their new diet. Both diets had the same amount of energy from protein, but with varying amounts of carbohydrate (5% in the ketogenic diet vs. 55% in the Western diet) and fat (75% in the ketogenic diet vs. 25% in the Western diet).

The study did not involve a keto-cycling diet. Instead, the participants followed a strict ketogenic diet throughout the study. This is an important distinction because the claim being made is about keto cycling, not a strict ketogenic diet. A number of the reported benefits of the diet were not actually demonstrated. The reference showed some results that were in line with the claim, such as an increase in lean body mass and total testosterone levels in the ketogenic diet group. However, the increase in lean body mass may be attributed to the reintroduction of carbohydrates during week 11, as noted by the authors: ”Given the probable nature of these assumptions, it is, therefore, likely that both groups gained similar amounts of muscle mass throughout the entire study.”. A large number of biomarkers were assessed, and the authors did not adjust for making lots of statistical comparisons for all of the biomarkers between the diet groups. Therefore, the difference in total testosterone may have been a chance finding. And, performance improvements in the bench press, squat or Wingate test (sprinting on a stationary bike) were not significantly different between the two diets.

Furthermore, the reference does not provide enough information about the diet the keto-cycling claim is being compared to, which limits the extent to which the reference can support the claim.

Reference 10

Reference

Chapter 1, reference 1. World Health Organization fact sheet and OECD (Organisation for Economic Co-operation and Development) document

Associated quote(s) and page number(s)

Page 18: “Since I was a medical student, 40 years ago, rates of obesity have almost tripled. Two billion adults are now overweight or obese, as are 39 million children under the age of five. If you look at the world’s major economies, the US has the highest rates of obesity, closely followed by Mexico, New Zealand, Hungary, Australia and then the UK.[1]”

Criterion 2.1. Does the reference support the claim?

4 out of 4

This reference received a score of 4, indicating that it offers strong support for the claim. For reference one, Fast 800 Keto includes two references, which are web links to a World Health Organization fact sheet and an Organisation for Economic Co-operation and Development (OECD) document.

The World Health Organization is a trusted organization. The fact sheet states that obesity has tripled since 1975, and over 1.9 billion adults aged 18 and older now live with overweight or obesity, and 39 million children under the age of 5. According to the OECD document, the US did have the highest rates of obesity in 2015, followed by Mexico, New Zealand, Hungary, Australia and then the UK.

Overall (average) score for reference accuracy

3.3 out of 4

Summary of the health-related intervention promoted in the book

The three stages of Fast 800 Keto are:

1. A short-term, 800 calorie, ketogenic diet for rapid weight loss.
2. A higher-protein, carbohydrate-reintroduction stage with intermittent fasting and time restricted eating for a slower rate of weight loss to meet the target weight.
3. A long-term, lowish-carbohydrate Mediterranean diet for long-term weight loss and health.

Stage 1: Short-term, 800-calorie ketogenic diet for rapid weight loss

In this stage, participants should consume enough protein and a low  carbohydrate intake to achieve ketosis. This stage lasts for a maximum of 12 weeks. Foods should be keto-friendly, including healthy proteins, leafy green vegetables, salads, and healthy oils. Meal replacements can be used if needed.

Stage 2: A higher-protein, carbohydrate-reintroduction stage with intermittent fasting and time restricted eating for a slower rate of weight loss to meet the target weight.

Stage 2 involves intermittent fasting and reintroducing complex carbohydrates. Participants should consume a Mediterranean-style diet with 50-120 g of fiber-rich complex carbohydrates and 60-80 g of protein per day on non-fasting days. Time-restricted eating is encouraged, starting with a 12-hour window and gradually shortening it.

Stage 3: A long-term, lowish-carbohydrate Mediterranean diet for long-term weight loss and health.

This stage is for long-term maintenance once the target weight loss or health goal has been reached. The focus is on a relatively low-carbohydrate Mediterranean-style diet with no calorie counting, rich in vegetables, legumes, yogurt, wholegrains, oily fish, olive oil, and nuts, and limited in processed meats, sugar-sweetened drinks, and pastries.

Across all stages, the book recommends avoiding ultra-processed foods. The plan offers flexibility in transitioning between stages, allowing individuals to skip stage 2 or gradually transition from stage 2 to stage 3 as needed.

The book clearly outlines potential safety risks and advises certain individuals to consult their medical professional before attempting the diet due to the extensive calorie restriction and rapid weight loss in stage 1.

Condition targeted by the book, if applicable

Overweight/obesity and type 2 diabetes

Apparent target audience of the book

The book is written for a general audience, but the diet is aimed at people who have a lot of weight to lose and metabolic problems (i.e., individuals living with overweight or obesity, and/or with pre-diabetes or type 2 diabetes). The diet is not suitable for a large number of individuals.

Criterion 3.1. Is the intervention likely to improve the target condition?

4 out of 4

The intervention scored a 4, indicating that it is likely to greatly benefit the target conditions for the target audience, compared to current Western diets.

The diet is similar to diets that are effective for rapid weight loss and improved metabolic health in clinical trials, with a low calorie diet followed by reintroducing food and then a long-term healthy diet. Overall, the diet would be expected to improve the target condition, with clinically meaningful weight loss and subsequent improvements in metabolic health at least 6 months later.

Stage 1 would likely result in large, rapid weight loss. Low-calorie diets are effective for weight loss and type 2 diabetes remission in people living with obesity (as discussed in Scientific accuracy Claim 1). A number of systematic reviews show that initial weight loss is a strong predictor of weight loss maintenance, with initial weight loss scaling with the duration and size of the calorie deficit. However, the strong recommendation for this low calorie diet to be very-low in carbohydrates to achieve ketosis would not be expected to provide additional weight loss or health benefits, with health benefits scaling with the calorie deficit and extent of weight loss. The book also recommends a food-based, low calorie diet over a total diet replacement low calorie diet, which has a smaller evidence base and higher risk of bias for its efficacy. Total diet meal replacements tend to be most effective for weight loss.

Stage 2 may help with adjusting to a long-term diet. Multi-stage diets used in clinical trials often reintroduce food after a total diet replacement for rapid weight loss. Intermittent fasting is infrequently discussed in the book, and really only mentioned in stage 2. It is unclear what the benefit is of being able to go into ketosis faster from intermittent fasting in stage 2, as people will already be in ketosis from stage 1. The ketogenic, intermittent fasting diet would not be expected to provide greater weight loss or health benefit over a non-ketogenic, intermittent fasting diet. Many of the benefits of intermittent fasting or time-restricted eating may simply be from reduced body weight/fat mass from a lower calorie intake. It is unclear how beneficial these recommendations would be in the context of the overall diet, and may just make adherence more difficult.

Stage 3 is a lowish-carbohydrate Mediterranean diet. A Mediterranean diet is one of the most well-studied diets for improving metabolic health, including type 2 diabetes, blood pressure, and reducing cardiovascular disease risk. However, the emphasis for a relatively lower carbohydrate intake would not be expected to provide any additional benefit. Moreover, the claim that a lowish-carbohydrate Mediterranean diet is the best diet for preventing weight regain is weakly supported. Currently available limited evidence indicates that a Mediterranean diet is likely to be as effective as any other diet for minimizing weight regain after weight loss.

Criterion 3.2. Is the intervention likely to improve general health in the target audience?

4 out of 4

The intervention received a score of 4, as it is likely to greatly improve general health for individuals living with overweight or obesity, and/or with type 2 diabetes, compared with current Western diets.

The rapid and extensive weight loss from stage 1 would benefit obesity-related conditions in the target audience, such as sleep apnea. Improvements in metabolic health, such as type 2 diabetes, non-alcoholic fatty liver and blood pressure would be expected to improve with the amount of weight loss. The long-term Mediterranean diet also has evidence supporting its benefits on cardiovascular health and cognitive function.

Fast 800 Keto recommends limiting ultra-processed food intake, and consuming foods such as leafy greens, nuts, olive oil, and vegetables at all stages. These foods are recommended across dietary guidelines. For the long-term Mediterranean diet, fiber-rich wholegrains, legumes, and pulses can be frequently consumed, which would benefit metabolic health. However, a low fiber intake from the extreme carbohydrate restriction in stage 1 (e.g. a lack of wholegrains, legumes and fruits) may lead to constipation. The recommendation for nuts and leafy vegetables in stage 1 may help with fiber intake.

Ketosis and intermittent fasting are unlikely to provide meaningful benefits in the context of the other recommendations, such as for cardiovascular health. Low-carbohydrate, ketogenic diets can lead to elevated LDL cholesterol and an increased risk of cardiovascular disease if foods are high in saturated fat, such as many animal-based foods. However, the Fast 800 Keto recommends avoiding such foods, and to opt for foods with healthy fats such as olive oil, avocados, nuts, seeds and fatty fish. This advice helps to minimize the potential increased cardiovascular disease risk, and would be expected to improve general health.

The recommendation for a slightly higher protein intake is unlikely to have significantly adverse consequences in the context of the overall diet, given that plant-based protein sources such as nuts, pulses, and legumes are recommended, alongside oily fish and lean meats.

The lifestyle advice in Fast 800 Keto would also promote general health and wellbeing.

Criterion 3.3. Does the diet portion of the intervention promote an adequate nutrient intake for general health in the target audience?

3 out of 4

The diet received a score of 3, indicating that it is likely to be more than nutritionally adequate.

Fast 800 Keto recommends avoiding ultra-processed foods, and eating a Mediterranean diet. As discussed in Criterion 3.2., a Mediterranean diet promotes food groups in line with public health guidelines for a healthy, balanced diet, and is recommended in health organization guidelines including the US Dietary Guidelines for Americans and American Diabetes Association guidelines. The diet contains a range of nutrients, vitamins, minerals, and phytonutrients, with minimal risk of any long-term nutritional deficiency as no food groups are explicitly excluded.

There is a risk of nutrient deficiency during stage 1 from the low calorie intake, and some participants may accidentally consume less than 800 calories per day. This would be a very-low calorie diet, and should have medical support. Stage 1 should also be low in carbohydrates, further restricting food choices. However, Fast 800 Keto does recommend consuming nutrient rich whole, minimally processed foods. A multivitamin/mineral is recommended, but to help with fatigue, rather than prevent nutrient deficiency.

A ketogenic diet may be unsafe for a number of reasons. The book indicates who should not follow the diet, including pregnant women, as well as people with a history of eating disorders, living with underweight, recovering from surgery, frailty, having a significant psychiatric disorder or ‘medical condition’, or on certain medications. It is unclear what defines a significant ‘medical condition’. This means the Fast 800 Keto diet is unsuitable for many people. The book recommends speaking to a doctor before starting the diet, particularly for people with type 2 diabetes, or if taking medication (e.g. insulin or blood pressure medications), given the impact on blood sugar levels. This advice reduces the risk of harm from the diet, or risk of nutrient deficiencies.

Overall (average) score for healthfulness

3.7 out of 4