The ketogenic (keto) diet is popular, polarizing, and represents the most extreme application of carbohydrate restriction. By rule, keto dieters consume 70-80% of calories from fat, while restricting protein (15-25%) and carbohydrate (<5-10%) intake. The premise of the diet is that restriction of carbohydrate (and, to some degree, protein) increases reliance on fat for energy, and increases the production and utilization of ketones as a fuel source. If protein or carbohydrate intake are too high, you’ll maintain some reliance on carbohydrate, and ketones will not be produced in sufficient quantities. From a biochemical perspective, the body adapts by enhancing its ability to derive energy from fat and ketones, and reliance on carbohydrate for energy is reduced. But aside from eliciting extreme viewpoints on the internet, what is keto actually good for?

 

Keto-Adaptation

Some cool things happen when these biochemical adaptations take place and you become keto-adapted. There are some seizure disorders that are caused by faulty carbohydrate metabolism in the brain. When these patients go on ketogenic diets, their brains learn to use ketones instead of carbs for energy, and the frequency and severity of their seizures are dramatically reduced [1]. In fact, the brain essentially becomes immune to hypoglycemia (low blood sugar) — even at blood glucose levels that would typically put someone into a coma, individuals who are keto-adapted from prolonged fasting are totally fine [2].

When it comes to body composition, there are some nice benefits as well. Most notably, ketogenic diets seem to reliably reduce appetite [3]. As I’ve noted in some previous articles and podcasts, I adhered to a ketogenic diet for a good six to seven months. I noticed a pronounced drop in appetite, but a very sustained energy level throughout the day. From a practical standpoint, it’s also very easy to avoid grazing or snacking when you’re on keto; it’s very rare that a catered meal at the office will involve palatable items that are >80% fat, so you’re faced with the choice of either eating butter packets or just sticking to the lunch you packed.

From my perspective, the most intriguing aspect of keto is its potential effects on exercise performance. The premise is appealing: If we carry tens of thousands of calories around in the form of stored body fat, and only a couple thousand calories of carbohydrate, why not get better at using the fat? Endurance athletes can experience gastrointestinal discomfort from pounding sports drinks and gels during events, and it’s inherently tedious. For these athletes, “bonking” or “hitting the wall” (i.e., running out of stored carbohydrate) is one of the primary performance killers they face. For strength and physique athletes, issues arise even before truly “bonking,” as evidence has shown that glycogen depletion happens in a non-uniform manner, with preferential depletion occurring near the sarcoplasmic reticulum [4]. This is problematic, as the sarcoplasmic reticulum is a huge regulator of the muscle’s ability to create force; as most carb-cutting strength athletes will tell you, lifting weights in a carb-depleted state is no walk in the park. So if we adapt to a keto diet, can we kick our carb dependence and become immune to these performance issues?

Unfortunately things aren’t that simple. We know for certain that after adjusting to keto for a few weeks, you will undoubtedly use more fat (and ketones) for energy, and less carbohydrate [5]. You’ll note that I haven’t been mentioning protein much, and that’s because you’ve got far bigger problems with your diet if a substantial amount of your energy for exercise is coming from protein. However, the benefits in fat and ketone utilization come at a cost.

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