Ketogenic Diet & Performance: The Basics

From Human Performance Resources by CHAMP at the Uniformed Services University
 
Periodically, ketogenic diets gain popularity in the athletic community for purported performance-enhancing effects. A ketogenic diet is one that’s very high in fat, moderate in protein, and very low in carbohydrates. Traditionally, KDs have been used to help treat children with epilepsy, a seizure disorder. At this time, the scientific evidence does not support that a KD is superior to current sports nutrition guidelines for improving performance. It also can be difficult to maintain a KD in the field or deployed setting due to its dietary restrictions.

What is a ketogenic diet?
There is no standard definition, but a typical KD is very high in fat (>75% of calories), moderate in protein (10–20% of calories), and very low in carbohydrate (<5% of calories). This means that an individual eating a 3,000-calorie KD would consume at least 250 grams of fat, 75-150 grams of protein, and no more than 40 grams of carbohydrate per day, which essentially eliminates grains, legumes, most vegetables and fruits, and selected dairy products (mainly milk). By comparison, a “normal” 3,000 calorie diet (based on the Military Dietary Reference Intakes) would contain up to 100 grams of fat (<30% of calories), 75-115 grams of protein (10-15% of calories), and 375-415 grams of carbohydrate (50-55% of calories).

How does a ketogenic diet work?

Consuming a strict KD over several weeks results in a state of ketosis. This refers to the build-up of ketones in the blood and/or urine. Ketones are molecules made by the liver from dietary fat, which your body then uses for energy. Since the body stores more fat than carbohydrates, some people think that being in a state of ketosis provides an almost “endless” supply of energy, from that fat.

Can a ketogenic diet improve my performance?
Even though KDs will increase your body’s ability to burn fat, the current scientific literature has not consistently demonstrated that a KD is superior to current sports nutrition guidelines for improving performance. Scientific evidence is mixed with regard to the effects of KDs on endurance performance. Physically active individuals and highly trained athletes who engage in low- to moderate-intensity exercise might not notice any improvements in endurance performance, while some might see improvements, and others might experience decreases in performance. There are typically "responders" and "non-responders" to any dietary intervention. It is important for individuals to find which type of diet best fits their lifestyle and metabolic profile.
 
If you’re participating in high-intensity exercise, such as sprinting, KDs can decrease performance. One explanation is not having enough carbohydrate to fuel the muscles. Ketones need oxygen to be converted to energy, but during periods of high-intensity activity your body generates energy without oxygen. Glucose, on the other hand, doesn’t need oxygen to be converted to energy.

What are the potential side effects of being on a ketogenic diet?       

Short-term side effects of KDs include nausea, thirst, headache, dizziness, fatigue, and increased urination. These side effects should subside once your body has “adapted” to a KD, but it isn’t clear how long that takes (usually one to four weeks). Also, any increase in carbohydrate intake will disrupt ketosis, and side effects can recur if you don’t strictly adhere to your KD. In other words, there are no “cheat meals” when you’re on a KD. Continued consumption of a KD can result in constipation and electrolyte imbalances, unless appropriately accounted for.

Debrief

KDs are not superior to current sports nutrition guidelines for improving performance, and it is unknown how the long-term use of KDs might affect a warfighter’s training, recovery, and injury risk. Remember that KDs are very restrictive and can be difficult for some to maintain because carbohydrates are present in nearly all foods, including grains, beans, legumes, fruits, vegetables, and dairy products. This is especially true in situations where you have limited food options or when operational rations are your only food source. Without a well-formulated KD, individuals can experience gastrointestinal symptoms and deficiency of several vitamins, minerals, and fiber. Individuals considering a KD should consult a qualified health care provider before starting a new diet.
 
For more information, read HPRC’s in-depth guide to the ketogenic diet.