By Eric Trexler, CSCS, CISSN
Former Director of Research and Education, INOV8 Elite Performance
I don’t post much on social media, but I do follow along to keep tabs on the world outside of my lab. I like to see what “the fitness people” are talking about, writing about, complaining about, asking about, etc. Every now and then, I stumble upon a thread about ketogenic diets. Each one of these threads is like a bad movie. They all assume a generic, formulaic structure, they are tedious to follow, and everybody walks out dissatisfied.
The structure is pretty simple and shockingly consistent. Someone makes a comment or shares a study about ketogenic diets, either positive or negative. Then a few people mock the diet with a clever cliché, sarcastic comment along the lines of “enjoy your butter dipped in butter, fried in butter— sounds healthy!” Then, the other group jumps in and aggressively promotes the magical properties of the diet. According to them, the diet is somehow ideal for all people, in all circumstances, regardless of their individual goals. It also happens to improve every type of athletic performance, alleviate the need to even think about caloric intake, and cure just about every disease known to man (or so I’ve read).
Unfortunately there is very little “middle ground” on the topic. It’s an extreme approach in terms of macronutrient composition, and it elicits extreme viewpoints. Further, it seems that those with the most polarizing opinions are also the most vocal. The discourse between the two closed-minded sides of this discussion is rarely productive, and does very little to help anyone understand the pros, cons, and applications of the ketogenic diet. I believe these types of discussions have brought undue criticism upon a viable approach to dieting, while simultaneously perpetuating myths about the actual benefits of ketogenic diets.
In order to see what a small sample of the bodybuilding-oriented population thought about keto, Matt Jansen put up a Facebook status soliciting opinions on the diet. Some viewed the diet as an ideal approach for bodybuilder, while others called the diet foolish or unsustainable. Some thought the diet offered protection against muscle loss while dieting, while others believe the diet increases muscle loss. There were individuals who thrived on the diet, individuals who tried (and despised) the diet, and a general consensus was that most people attempting “keto” actually fail to achieve a sustained state of nutritional ketosis due to incorrect intakes of protein and fat.
Ketogenic diets typically entail high fat intake (70-80% of calories), moderate protein intake (15-25%), and low carbohydrate intake (<5-10%). In order to induce ketosis, the dieter must not only restrict carbohydrate, but also limit protein to some degree— if not, the high intake of amino acids will increase gluconeogenesis to a degree that inhibits ketone formation. Previous research has demonstrated that ketogenic diets are beneficial for individuals with certain seizure disorders and conditions related to defective metabolic pathways . There is also evidence to suggest that such diets may suppress appetite  and help to preserve lean mass . Emerging research is investigating the role of nutritional ketosis in cancer; rodent data has suggested that a ketogenic diet could potentially reduce the growth and metastasis of cancerous tumors , but more research is needed to verify these preliminary findings in humans.
That being said, ketogenic diets are not the magic cure-all that some claim them to be. Many claim that carbohydrate restriction is far superior to all other dietary approaches in the context of long-term weight loss. Despite some positive findings , research to date has failed to demonstrate a clear, consistent superiority of low-carb diets in comparison to low-fat diets [5, 6]. This debate rages on, as nutritional ketosis is a fickle state that must be maintained to derive the theoretical benefits of the diet. As such, keto-advocates often claim that research fails to demonstrate keto’s superiority because the low-carb diets examined aren’t “keto enough” (i.e., they don’t truly induce a sustained state of nutritional ketosis), or the interventions do not allow sufficient time to become keto-adapted. The body of research is further clouded by unequal protein intakes between various diets; in a number of previous studies showing low-carb or ketogenic diets to be better than low-fat diets, the benefits of the lower-carb approach could potentially be attributed to comparatively higher protein intakes in the low-carb group.
I believe keto is a very viable approach to weight loss diets, which some people (myself included) may prefer compared to a low-fat diet. I also suspect that there may be value in the hunger-suppressing and lean mass-preserving effects of nutritional ketosis, and I agree that many studies using a “very low carbohydrate” group may be insufficient for inducing ketosis. It is entirely plausible that future, well-designed trials may demonstrate that these theoretical advantages consistently translate to better weight loss success, and this is a line of research I’d be very interested in pursuing. However, until more research surfaces comparing appropriately designed ketogenic diets to protein-matched low-fat diets, keto advocates are obligated to use a bit more tempered language with their claims about the diet. When it comes to weight loss, it would probably be appropriate to say that no diet seems to be markedly more effective than keto. However, there is not yet sufficient evidence to conclusively claim that keto stands head and shoulders above all other diets.
Occasionally, I hear people claim that ketogenic diets enhance athletic performance. It has been surmised that ketogenic diets may enhance endurance performance as they increase the capacity for fat oxidation, and humans can yield far more ATP from stored body fat than from stored glycogen. Thus, by becoming keto-adapted and primarily metabolizing ketones and fat for energy, endurance athletes would have abundant energy stores throughout the race and potentially avoid bonking, especially in very long races. Research to date has failed to show a consistent benefit for endurance exercise , and some research has indicated a potentially ergolytic effect on high-intensity exercise [8, 9]. Research in this area is fairly inconsistent, as other studies have shown ketogenic diets to have no effect, or even be beneficial, for both low- and high-intensity exercise [10-13]. Such inconsistencies may relate to the design of the diets used in such studies, the time provided to allow keto-adaptation, and the exercise test evaluated. For the exercise duration and intensity employed by most trainees, it is unlikely that ketogenic diets provide a marked performance advantage. Some research has suggested that keto does not hurtperformance, but other studies have observed an ergolytic effect, especially in exercise bouts of high intensity.
Along the same lines, it is also common to see people exaggerate the evidence pertaining to ketogenic diets and cancer. The data emerging in this area is intriguing, and quite promising. Rodent research has indicated that ketogenic diets may reduce the growth and metastasis of cancer , and that these effects can also be observed in the context of ketone supplementation, even in the absence of carbohydrate restriction . This line of investigation is largely based on the unique metabolic properties of cancer cells; specifically, cancer cells tend to function almost exclusively by glycolytic metabolism, and have an extremely limited ability to metabolize fats or ketones for energy . Some researchers have also suggested that circulating levels of blood glucose and/or insulin may play a role in cancer development and growth [15, 16], which has bolstered further interest in the potential of carbohydrate restriction in cancer. I personally have great hope for this line of research and eagerly await more human data. However, despite the emergence of promising rodent data and a strong theoretical basis, more human data is needed before definitive statements can be made about keto and cancer.
The ketogenic diet certainly has positive attributes. I have followed a ketogenic diet for an extended period of time and find it to be a convenient, palatable dietary approach that helps to reduce my appetite and support sustained energy levels throughout the day. But that is not to say that the diet is free of drawbacks. Very low carbohydrate intakes can sometimes provoke dieters to eliminate a large number of carbohydrate-rich foods from their diet entirely, and can put some limitations on the amount and type of fruits and vegetables consumed. If the diet is not mindfully constructed, this can make it a bit more difficult to achieve a diverse intake of micronutrients. This doesn’t mean that the diet guarantees a micronutrient deficiency; rather, the dieter must take proactive steps to ensure sufficient micronutrient intake. Further, the first couple weeks of the diet require an “adaptation” process, in which people may feel sluggish, get headaches, or experience some gastrointestinal discomfort. I found these symptoms to be very minor and short-lived, and I believe the symptoms are most pronounced in the context of poorly formulated ketogenic diets. Despite this brief adjustment period, I experienced the same effect that Dr. Jeff Volek has mentioned from his studies on ketogenic diets: When participants are able to revert back to higher carbohydrate intakes after a study is complete, they often choose not to. As such, I have elected to continue my ketogenic diet for the time being based on my personal preferences.
I think it’s safe to say that keto isn’t a “stupid” approach to eating, nor is it a dietary savior. When a well-designed ketogenic diet is employed, the dieter can experience a palatable, convenient diet that can fit their preferences and help to suppress appetite, sustain energy levels, and provide the nutrients necessary for good health. There is strong evidence to suggest that keto is great for a number of seizure disorders and metabolic disorders, and that ketogenic diets may reduce hunger. Evidence has shown that keto is a viable approach for weight loss and the management of type 2 diabetes, performing as well (or better) than other diets in clinical trials. While the emerging research pertaining to ketogenic diets and cancer is promising, more human data is needed on the topic. Further, while most people are unlikely to obtain a performance benefit from a ketogenic diet, many are able to maintain performance despite carbohydrate restriction. Ultimately, this may come down to details of the diet and training program employed. The ketogenic diet is therefore a viable dietary approach with a number of pros and cons, much like any other method of dieting.
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