I am a bit divided on the benefits of a ketogenic diet and physical performance. The evidence, in my opinion, is somewhat equivocal and largely dependent upon specificity. For the athlete, performing explosive, high-intensity movements, I am inclined to not recommend a ketogenic diet. For others, specifically those involved in longer endurance events or those more sedentary individuals looking to lose body fat, I am inclined to suggest it may not matter.
The challenge with a keto diet and performance is that the preferred fuel for muscle contraction is muscle glycogen. When glycogen is depleted, performance tanks. Athletes do not want to risk impaired performance.
Ketosis occurs when there is insufficient muscle glycogen to fully metabolize fat. In exercise physiology, we learn that “fats burn in the flame of carbohydrate”. In short, fat metabolism requires that free-fatty acids be broken down through a process called “beta-oxidation” into 2-carbon molecules of acetyl Co-A which join oxaloacetate (a by-product of the tricarboxylic acid cycle, commonly known as the Krebs cycle) to enter the Krebs cycle. When muscle carbohydrates are low (e.g, with a very low carbohydrate diet or fasting), oxaloacetate is converted to pyruvate and the Krebs cycle is essentially shut down. Fats get converted to ketones and only a fraction of the potential adenosine triphosphate (ATP; the fuel for muscle contractions) is produced. These ketones can be used for energy elsewhere (e.g., the brain—which is why the ketogenic diet is promoted for mental clarity), but fat is burned at a much greater rate. The body isn’t completely void of glucose, though. Fats, specifically triglycerides, break down into free fatty acids and glycerol. The liver can convert glycerol and some amino acids into glucose to be stored in the muscle and liver as glycogen, but ingesting glucose is far more efficient. This is the “Reader’s Digest version” of ketogenic fat metabolism, but I don’t intend of this to be a lecture on fat metabolism. I do believe it is essential to have some understanding of how the ketogenic diet works to form a foundation upon which to make a decision about whether the ketogenic diet is appropriate.
Who should consider a ketogenic (AKA “keto”) diet? The keto diet is most beneficial for people who want to burn excess fat quickly and effectively or maintain a low body fat percentage. It is important to remember, however, that weight management is most dependent on caloric balance. To lose fat, one still needs to be in a net hypocaloric state. Too many calories on a high-fat/very low carbohydrate diet will still lead to a net gain (though it is much harder to over eat on a high fat/low carb diet than a high carb/low fat diet—fats contribute to greater satiety and better insulin regulation). The ketogenic diet was originally developed for the treatment of epilepsy. There may be some health benefits that are inconclusive at the time.
Who should not consider a keto diet? I would suggest that athletes should not consider a ketogenic diet. Ultra-endurance athletes may be able to manage because they train and compete in a more fat-dominant metabolic state, but I would think that such an athlete would then require exogenous ketones (those ingested as ketones rather than those resulting from the breakdown of stored body fat or ingested fat) because the amount of stored body fat will already be low from the intensive amount of calories burned in training and competition.
Some research on the keto diet has be initiated by the Department of Defense. Eating frequent regular meals can be challenging for our elite combat forces. Sustaining mental acuity and preventing hunger is essential. Keto appears to have positive benefits in this regard. It should be noted, however, that these too likely require exogenous ketones to maintain caloric needs.
One very important consideration with regards to the ketogenic diet is compliance. It is an easy diet to follow—simply eat moderate protein and high fat, keeping carbohydrate extremely low (usually less than a net of 50 g per day—often as low as 20-30g)—but it is also extremely hard given the necessary lifestyle restrictions. It is much harder to dine out and socialize on the keto diet. It is not impossible, but certainly difficult. Alcohol is limited to fewer than one to two drinks (as one should, anyhow)—preferably dry wines and clear alcohols. (There are supposed to be keto-friendly beers, but I haven’t tried them—and I suspect they are not the best. So, if you are a beer drinker….) Desserts are even more challenging (maybe worse than trying to be gluten-free). There are some decent keto-friendly desserts, but one probably has to go out of their way to find them. Dark chocolate is allowed, but watch the net sugars—not all dark chocolate is the same.
Something to remember when considering the ketogenic diet is that it takes a few weeks to adjust. One may feel sluggish at first, and initially performance will be impaired. To get the best results one needs to be consistent. It takes commitment. It is not something to be done on and off again.
Personally, I am less inclined to go keto. Still, I find limiting carbohydrates effective for my metabolism. In particular, I find I need to limit breads and grains to lose fat—but, I don’t go overboard. What I find to work for me—and to be sustainable is to follow more of a hybrid of intermittent fasting, keto, and balanced hypocaloric eating to lose or maintain weight. Rather than a traditional American breakfast (i.e., high-carb, mostly grains and fruit), I start with a buttered coffee (coconut oil and grain-fed butter added to my otherwise black coffee) and delay my first meal as long as I can—which is actually easy since the buttered coffee leaves me feeling fuller longer. I focus on proteins and vegetables for lunch and snack on proteins and nuts. By dinner, I have calories to spare and less likely to go overboard on carbs. I might do better going much lower on carbs, but I like the flexibility of just limiting carbs based upon my training. (I prefer to follow Renaissance Periodization’s recommendation of 0.5 g/lb on non-training days, 1.0 g/lb on light training days, 1.5 g/lb on moderate training days, and 2.0+ g/lb on intense training days. Since I train more frequent shorter workouts, 0.5-1.0 g/lb seems best for me. That is roughly 55-110 g per day. This is low but not ketogenic.) If I shoot to be ketogenic, I am likely to fall short, but, overall, my calories remain lower and I still feel pretty good. I don’t have to panic if I am eating out or a guest in someone’s home.
Some can make keto a lifestyle. Others, like me, cannot. Like any diet, it should not be regarded as a short-term weight loss strategy. The best fat loss (and other purported benefits of a keto diet) will come from sustainable lifestyle changes. One might choose to go “keto” for a six week “cut phase” to lose body fat quickly (this is not uncommon with bodybuilders), but once the person goes back their old habits, the fat will return (if the diet is hypercaloric). Thus, with care, a period of ketogenic “dieting” may be beneficial as part of a planned weight management strategy (i.e., periodization plan).
Keto is trending as one of the most popular diets. It will be effective for losing fat. If sustainable, it may have health benefits. How it affects performance will be highly individualized, depending on genetics and specificity. Choose wisely. Choose what is most suitable for you. If you are considering “going keto”, do your homework. It is not a matter of just eating bacon, eggs, and avocados. Fiber (or lack thereof) is a consideration, as is certain nutrient deficiencies. It is also important to remember that caloric balance is the most important consideration in managing body fat. You can overeat on the a ketogenic diet.
Most ketogenic diets will be about 75% fat, 20% protein, and 5% carbohydrates. (A more traditional diet is 40-65% carbohydrate, 20-35% fat, and 20-30% protein.) In a 2000 kcal diet, that is roughly 167 g fat, 100 g protein, and 25 g of carbohydrates. For comparison, one slice of Dave’s Killer Bread (21 Whole Grains and Seed, my favorite) has 22 g of carbs (120 kcal; 5 g fiber; 5 g sugar), a medium apple has about 25 g of total carbs (100 kcal; 4 g fiber; 19 g sugar); and a cup of steamed broccoli has only 12 g of total carbs (54 kcal; 5 g fiber; 2 g sugar). I am learning to replace rice with cabbage or riced cauliflower. One cup of cooked cabbage has 8 g of total carbs (34 kcal; 3 g fiber; 4 g sugar). One cup of riced cauliflower has 5 g of total carbs (25 kcal; 2 g fiber; 2 g sugar). An equivalent serving of whole grain brown rice has 46 g of total carbs (220 kcal; 4 g fiber; 1 g sugars)—white rice has 53 g of total carbs (242 kcal; <1 g fiber, <1 g sugar). A goal in any diet is to choose foods that are the most nutrient dense—i.e., have the most vitamins and minerals relative to total calories. Keto is high in fat, but fat choices also matter. Choose carefully.
The key to success for any diet is making lifelong changes that work for you. Keto is not for everyone. Of course, no diet is for everyone. Do what works and stick to it.
Be your best today; be better tomorrow.
Carpe momento!