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All right, welcome everyone to a new episode of Myth Busting, where every Monday we're going to take a look at some popular fitness or nutrition idea, look at where that idea got started, and then figure out whether it's true or false based on the most recent scientific literature. So this week we're going to be looking at the idea that ketogenic diets are better than conventional diets for fat loss, and we'll also touch on a few other things like general health and performance.
So first, where did the keto diet come from? In the early 1900s, medical use of the ketogenic diet emerged as a strategy to treat epilepsy. In 1921, Dr. Russell Wilder coined the term ketogenic diet, named for the presence of ketone bodies that increase in the blood when carbohydrates coming from the diet are too low to serve as the body's main fuel source. It was found, and continues to be, a very effective treatment for epileptic seizures. However, it wasn't until the 1970s, with the release of the Atkins diet, that very low carb diets gained mainstream popularity. While most of Dr. Atkins' ideas were rejected by sound medical science, there has been a resurgence in the popularity of the ketogenic diet in the last few years, especially within fitness circles.
Quickly, a ketogenic diet is basically a very low carb, very high fat diet. In practice, calories from carbs are often brought all the way down to 5% of total caloric intake, with about 20% of calories coming from protein and about 75% from fat. Generally, carbs are restricted to no more than 50 grams per day, and most of those carbs tend to come from more fibrous sources like vegetables, with only trace amounts in foods they're already eating.
So why do people think this is a good idea for fat loss? I've seen two main reasons given amongst its strongest proponents. The first is the insulin hypothesis. The idea goes that since one of insulin's main actions is lipogenesis, or fat formation, keeping insulin levels low by restricting carbohydrate in the diet should result in less fat storage and more fat mobilization. Now, I covered this in a video on sugar, but very quickly: while it appears to be theoretically sound, there are a number of problems with the insulin hypothesis. First, it has been experimentally falsified for being too simplistic. Specifically, I think it's important to remember that carbs are not the only nutrient that spikes insulin. Protein itself is also very insulinogenic, and insulin is not required for fat storage to take place. So even if you're on a zero carb diet, if you're in a caloric surplus, fat can still be stored because of a hormone called adipose stimulating hormone, or ASH. It's quite clear that a prolonged energy surplus is the main factor driving fat gain, and not a single hormone such as insulin.
The second main claim from keto proponents is that the keto diet offers some sort of metabolic advantage over more conventional diets. The basic theory here is that it's more energetically costly for the body to convert proteins to glucose, so in the absence of dietary carbs, the body is forced to waste energy, or waste calories, converting protein to glucose. As a result, it burns more fat. Again, while that sounds like a reasonable hypothesis, according to one 2013 review there is no direct experimental evidence to support a metabolic advantage, and a recent study reported no changes in resting energy expenditure after a very low carb ketogenic diet. As a whole, the scientific community has pushed back against this idea quite harshly, with no evidence really ever turning up in support of it. To me, looking at this body of literature as a whole, rather than offering some unique metabolic advantage, it seems much more likely that the keto diet is just quite good at suppressing appetite. That is an effect that's been noted repeatedly in the scientific literature.
I'd also note that restricting carbohydrate isn't the only way to reduce appetite and control hunger. For example, a lot of people notice improvements in hunger control when using intermittent fasting, regardless of carb intake, and even simple strategies like increasing your water intake or fiber intake can definitely help increase fullness and satiety, again regardless of overall carb intake. Also, with keto you're eliminating many foods, meaning your options are more limited, so it could be the case that people simply consume fewer calories without realizing it, just because some of the more appetizing aisles of the grocery store are off limits. So rather than a unique metabolic advantage, it seems much more likely that keto just gets people eating fewer calories through reduced appetite and food elimination. The former can be achieved through other, less aggressive means, and the latter isn't necessary, since you can impose a caloric deficit without eliminating whole food groups.
But so far, all we've really done is address hypotheses surrounding keto, so now let's look at what the actual experimental literature has to say. A 2014 meta-analysis published in the Journal of the American Medical Association, looking at 48 studies on the efficacy of different popular fad diets like Atkins, Weight Watchers, and so on, found that pretty much all diets result in significant weight loss. This led the authors to conclude that most calorie-reducing diets result in clinically important weight loss as long as the diet is maintained, and that any differences were small and likely unimportant. For example, even though the Atkins diet did result in slightly more weight loss than the Zone diet, because different diets are variably tolerated by different individuals, the ideal diet is the one that is best adhered to, so that people can stay on it as long as possible.
Another meta-analysis compared low-carb diets to calorie-matched conventional weight loss diets in overweight adults and found that trials show weight loss in the short term irrespective of whether the diet is low carb or balanced in terms of macronutrient composition. Granted, low-carb is not the same thing as keto, so for that we turn to the results of a 2013 meta-analysis from Dueño and colleagues, which only included studies that restricted carbs to less than 50 grams per day. Here things get a little more interesting. Looking at the graph, there was a statistically significant effect in favor of keto for weight loss across these thirteen studies, although it's only about one kilogram of difference on average. Even the authors acknowledge that in the long term, and when compared with conventional diets, the differences appear to be of little clinical significance. Other researchers have also pointed out that protein intake tends not to be controlled in these studies, where the keto group usually just ends up eating more protein in place of the carbohydrate the diet is missing. This is likely to result in increased weight loss, since first, protein is more thermogenic than carbohydrates or fats, meaning it requires more energy to be metabolized, and second, protein is more satiating than the other macronutrients, meaning subjects are more likely to eat fewer calories simply because they feel more full from the increased protein.
In support of this idea, a 2012 study from Sonia Nataal split 132 subjects into four calorie-matched groups. They had two normal protein groups, one with normal carbs and one with low carbs, and two high protein groups, again one normal carb and one low carb. After one year of dieting, they found no differences between normal carb and low carb groups if protein was matched, and they also found that a high protein diet outperformed the normal protein diet in both cases, regardless of carb intake. To me, this indicates that protein is more likely to be a central factor in the success of a weight-loss diet than carb intake, and this isn't even mentioning its positive effect on preventing muscle loss.
It's also worth mentioning that many people will see initial success with keto, losing a lot of weight quite quickly due to glycogen depletion and water loss. But after those first few weeks, the weight differences between keto and a more conventional balanced diet start to go away, and it becomes a question of diet sustainability. Some people have adopted the keto lifestyle with quite a lot of success, even over the long term, but others may find it more difficult to stick to, especially in the beginning. In the absence of any specific benefit to keto, this is a deterrent that calls into question its generalizability as a successful dieting strategy. Even if we can see that really any diet will be successful provided a caloric deficit is imposed, some folks will still point to other potential benefits of a ketogenic diet, such as improved insulin sensitivity and cardiovascular health.
As far as insulin sensitivity and diabetes go, a 2018 report from the American Diabetes Association found that while some studies have shown modest benefits of very low carbohydrate or ketogenic diets, this approach may only be appropriate for short-term implementation, up to three or four months, and only if desired by the patient, as there's little long-term research showing benefits or harm. Even if you already have diabetes, there's no single ideal dietary distribution of calories among carbohydrates and fats, so macronutrient distribution should be individualized while keeping total calorie and metabolic goals in mind. When it comes to cardiovascular health, there isn't any consistently found benefit in the literature. One meta-analysis looking more into the cardiovascular side of things did find significantly greater increases in HDL cholesterol and LDL cholesterol on the low carb diet, while systolic and diastolic blood pressure didn't differ significantly between the groups. Given the highly multifactorial nature of cardiovascular disease, I would say the practical significance of any differences between calorie-matched keto and normal carb diets is questionable.
From a more common-sense perspective, keto might make it, at least initially, a bit more difficult to eat nutritiously, since you're eliminating a very wide range of food options. Whole grains and their nutrients wouldn't be as easily available to you. While there is generally room in a ketogenic diet for green leafy vegetables because of their low carb content, fruit often doesn't make the cut. I would say that limiting fruit in your diet probably isn't the best way to optimize your diet for health, especially considering fruit is very nutrient rich and, unlike a lot of vegetables, also quite enjoyable to eat.
So is keto the key to health and longevity? I would say probably not. By the same token, it also won't kill you, since the body doesn't seem to have any real problem with ketosis once it's adapted, and carbohydrates aren't an essential nutrient, so you don't need them in your diet.
Finally, I'd like to touch on keto's impact on strength and muscle building goals. Good data here is somewhat limited, since most of the trials showing a benefit of keto don't control for protein intake, so it isn't surprising that the keto group often comes out on top. However, a recent study from Wilson and colleagues matched calories and protein between groups and found similar increases in strength and power between a ketogenic diet and a Western diet, suggesting that a keto diet might have less ergolytic performance-reducing potential for strength training than it does for endurance training. In other words, I think keto is probably worse for endurance training than strength training, but it's probably not really helping either of them. More grimly, a 2015 paper from Burke and colleagues notes that fat adaptation strategies like the keto diet might impair exercise performance, particularly in shorter, high-intensity events, which is likely due to impaired muscle glycogen utilization needed to support high work rates. So I would say that, assuming calories and protein are matched, there's no real benefit to going keto for absolute strength and size, although there does seem to be a potential risk as far as performance goes.
Bringing this full circle, I would say the idea that the ketogenic diet is better than a balanced, more traditional diet is busted. While there always will be individual differences, and some people do seem to do quite well on keto, I think this ultimately comes down to personal preference and individual trial and error. I will note that while I haven't personally experimented with keto myself, I know many people who have, and from what I hear, it can be pretty brutal to adapt to, especially in those first few weeks. People often feel quite nauseous and lethargic, and it's gotten the moniker "keto flu" for that adaptation period. So the barrier to entry for a keto diet is quite a lot higher than for other diets, and even though it is only temporary and you do eventually adapt, this could be seen as a deterrent, especially since, as I said, there doesn't appear to be any obvious long-term benefit to keto anyway.
Looking at the evidence as a whole, I wouldn't say there's any obvious metabolic advantage, fat loss advantage, performance advantage, or even any health advantage to the ketogenic diet. That said, there doesn't seem to be any obvious real detriment to any of these areas either. So if you are running the ketogenic diet now with some success, I think you should stick to it as long as it continues to work for you. It's also worth noting that the ketogenic diet may have applications in the treatment of certain cancers, certain skin conditions, epilepsy, and other neurological disorders. But when it comes to otherwise healthy individuals, it's important to keep in mind that while things get more complicated the more you zoom in, the best diet is usually the one to which you can best adhere.
Here I'm Jeff Nippard, that's going to wrap up this week's Myth Busting. I hope you really liked it, and thank you so much for watching. Before we go, I want to give a huge shout-out to Squarespace for again sponsoring this Myth Busting Monday. In case you don't know, Squarespace is an all-in-one website platform that allows you to custom create your own website and online store, and it's the service I've been using for the last few years to run my own fitness website and business. If you're looking to get started with your own website, I recommend going to squarespace.com/nippard, which will save you 10% off your first purchase. They have beautiful designer custom templates and 24/7 customer support. Don't forget to leave me a like if you liked the video, and don't forget to subscribe if you happen to be new. I will see you all here next Monday.