Chances are in the past few years you have come across the Ketogenic or ‘Keto’ Diet – which is nothing but a reincarnation of the super low carbohydrate diets such as the Atkins & South Beach diets. Credit where credit’s due – the proponents of this dietary framework have been extremely clever with their marketing strategy which has resulted in a wide circulation of their message. Keto proponents claim that this diet can effectively turn a body into an efficient ‘fat-burning’ machine that is also better at regulating blood glucose. These are certainly attractive claims for anyone wanting to stay thin (which, let’s be honest, includes most of us) and particularly anyone who suffers from any type of Diabetes, so I completely understand why many of us are turning to this diet as some form of panacea. After all, as a society, we have never been more overweight, and rates of Type 2 Diabetes – which is a lifestyle disease – are soaring across the world. But being the science nerd that I am – I really wanted to separate fact from fiction and understand where the science lies. Are these claims supported by the literature? Beyond marketing and agenda-setting, what is the truth about the Keto Diet? To do this, I set out to answer 4 questions:
Before we jump into the science, it’s important to understand the specifics behind this dietary framework. Followed properly, a ketogenic diet consists of a very low amount of carbohydrates (20-50g/day), a moderate amount of protein, and a very high amount of fat (70% or more of total calories). By depriving the body of glucose, the body’s primary fuel source which is provided by carbohydrates, the body transitions to a state of ‘ketosis’ whereby it begins to produce compounds called ‘ketones’ that are used for energy. Essentially, this is a survival mechanism whereby the body is able to keep creating energy using a secondary source, derived from fat, until the person can consume carbohydrates again. As you can imagine, this process would have been extremely useful for our ancestors when food supply was scarce and their next meal was rarely guaranteed. Today, however, with the abundance of food we are spoiled with in the western world, this survival mechanism is simply made redundant.
In theory, the thinking goes, if a Keto Diet can make a body switch from producing energy from glucose to a body that “burns fat”, this would mean greater fat loss and thus a leaner body mass. Less fat around the thighs, bum and/or waist – happy days! An attractive theory no doubt – but unfortunately, that’s not really how it works. Unless you are in a calorie deficit, when in ketosis you are simply using the energy from dietary fat, not stored fat. This is a distinct point that many keto proponents often fail to mention. Fat burning is very different from fat loss. In fact, to actually tap into your body’s fat stores and shed some weight, you need to be burning more calories than you consume (a calorie deficit). This is why a study that compared a ketogenic diet to a high carbohydrate diet with equal calorie intake found zero differences in body fat loss . So yes, people following a strict Keto diet will be in ketosis and thus utilise fat as their primary source of energy, but, just like any other diet, unless they fall into a calorie deficit, they are not burning stored body fat – just the fat they are eating.
So why then do people seem to anecdotally lose weight when they switch to a ketogenic diet? There are two major reasons that explain this phenomenon. The first and super obvious one is glycogen. The average person stores about 500g of glucose in their muscles as glycogen. Each gram of glycogen attracts 3g of water. Thus, when you switch to a keto diet, the body utilises all of its glucose stores before falling into a state of ketosis – this process alone results in a drop of about 2Kg. But friends, it’s important to note this is purely scale weight and is again not a reflection of actual fat loss. I can see how this very sudden drop in scale weight acts as an initial motivator and is what hooks people to the Keto Diet. However, far from being a miracle diet, it is nothing but a misleading occurrence, and a somewhat dangerous one: many studies have shown that maintaining glycogen stores is absolutely crucial for optimal recovery, performance and overall exercise capacity .
The other reason that the Keto Diet helps people lose weight, which I actually think is a positive aspect, is that by encouraging the consumption of an extremely limited amount of carbohydrates per day, it means that by default people cannot eat their favourite refined junk foods. All of a sudden, chocolate bars, doughnuts, pastries and fried potato chips are categorically off the menu. This is likely going to result in a significant calorie deficit for a lot of people. But it’s important to appreciate that this isn’t some magic weight loss process and you can, in fact, remove heavily refined junk foods (e.g jelly beans), whilst still keeping healthful carbohydrate-rich foods in the game (e.g black beans), and also lose weight.
Perhaps the most concerning of the claims made by keto proponents is the idea of “reversing insulin resistance and Type 2 diabetes.” Addressing the totality of the science surrounding Type 2 Diabetes is beyond of the scope of this article (this topic was addressed in an article I wrote with Dr Michelle McMacken) however, in short, to reverse insulin resistance or Type 2 Diabetes it is necessary to improve one’s someone’s ability to tolerate carbohydrates. Two of the major ways we can achieve this is by changing the types of food someone eats with or without the presence of weight loss. A keto diet may help control blood glucose, however, without weight loss, it will not improve insulin sensitivity. What’s the problem with this? It means one would need to continue to eat a low-carbohydrate diet for the rest of their life as the underlying cause of their disease has not been addressed, and in fact, is likely to have been made worse by higher amounts of ectopic fat stores in muscle and liver cells.
On the other hand, unlike a keto diet, a low-fat wholefood plant-based diet has been shown to improve insulin sensitivity even without weight loss. By merely changing the food one eats it is possible to achieve an almost instant change in insulin sensitivity. In fact, several trials have been published where Type 2 Diabetics who adopt a low-fat plant-based diet have been able to completely come off their medications [3–6]. It’s also important to keep in mind that the #1 cause of death for diabetics is cardiovascular disease and that the lowest levels of cardiovascular disease are consistently found among populations that get the majority of their calories from wholefood plant sources of carbohydrates such as the Indigenous Tsimané people in Bolivia and plant-based Seventh Day Adventist’s in California & Canada [7,8].
The evidence is clear: across the world, no population consuming a low carbohydrate diet fares well in terms of longevity, and in fact, research suggests that in the long-term, people who adopt such diets have a higher risk of premature death . Low carb proponents often point to the ‘Inuit Eskimos’, a population who consume a very high-fat diet made up of almost exclusively animal products, to defend their position. However, it’s been well-documented that the original claims of this population experiencing a low incidence of cardiovascular disease were based on anecdotal rather than empirical scientific evidence . In fact, compared to non-Eskimos from nearby populations, the Inuit population actually have the same risk of heart disease, twice the risk of stroke and a shorter life expectancy of around 10 years . Studies going back over 1,000 years have also reported the presence of heart disease in frozen Eskimo mummies .
This is likely because a high-fat diet made up of almost exclusively animal products contains foods associated with increased LDL cholesterol and cardiovascular disease risk and that’s exactly what we see in the science [12–15]. A recent study compared a keto style diet (less than 20g of carbohydrates per day) to a control diet and in just 3 weeks found that the subjects on the low-carbohydrate diet experienced a 44% increase in LDL cholesterol .
Overall, basing recommendations for a low carbohydrate diet on anecdotal evidence from the Inuits ignores what we know about high-fat diets and cholesterol as well as a plethora of evidence that we have on how the longest living populations in the world eat. We know that people who consume higher amounts of dietary fibre, a nutrient found in carbohydrate-rich plant foods, and lower amounts of total dietary fat, particularly saturated fat, experience a significantly reduced risk of developing major chronic diseases . Adopting a keto diet, and therefore restricting your dietary fibre intake, is risky business.
One of the biggest problems with low carbohydrate diets is that they are not sustainable and that in the long run, they almost always lead to weight gain. On the other hand, we know from several studies, randomised trials and population studies that adopting a wholefood plant-focused or exclusive diet helps people maintain a healthy body weight without having to count and track calories [2,17].
Finally, when talking about sustainability we need to touch on the health of our planet. Typically, a keto diet is made up of a large number of animal products (fatty cuts of meat, full-fat dairy and eggs) which we know require far greater water inputs and produce significantly more greenhouse gas emissions than plant-based foods . For example, for an equal amount of protein, the production of cheese produces approximately 14 x more greenhouse gas emissions than that of legumes .
In summary, there is no evidence to suggest that when calories are matched a typical keto diet is better than any other diet in terms of weight loss, we have no data to suggest its a healthful way to eat in the long term, and in its typical form it’s a diet that places great strain on our already severely damaged environment. What about a vegan keto diet? While at a high level it appears to be better for human health, planetary health and animal welfare, there is still a lot more science needed to before one can confidently recommend it as a safe and healthy dietary framework to follow long term.
My recommendation is to look past the sexy headlines and adopt a carbohydrate-rich wholefood plant-focused or exclusive diet that is sustainable for both you and the planet and at the same time will help you achieve the health & performance goals you desire. To help identify what this might look like, I have developed a science-based Healthy Plant-Based Food Pyramid so you can easily construct countless delicious meals while making sure you are fueling your body the right way.
 Hall KD, Chen KY, Guo J, Lam YY, Leibel RL, Mayer LES, et al. Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men. Am J Clin Nutr 2016;104:324.
 Barnard ND, Cohen J, Jenkins DJA, Turner-McGrievy G, Gloede L, Green A, et al. A low-fat vegan diet and a conventional diabetes diet in the treatment of type 2 diabetes: a randomized, controlled, 74-wk clinical trial. Am J Clin Nutr 2009;89:1588S.
 Kaplan H, Thompson RC, Trumble BC, Samuel Wann L, Allam AH, Beheim B, et al. Coronary atherosclerosis in indigenous South American Tsimane: a cross-sectional cohort study. The Lancet 2017;389:1730–9. doi:10.1016/s0140-6736(17)30752-3.
 Wright N, Wilson L, Smith M, Duncan B, McHugh P. The BROAD study: A randomised controlled trial using a whole food plant-based diet in the community for obesity, ischaemic heart disease or diabetes. Nutr Diabetes 2017;7:e256.
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