One of the biggest controversies in the sports nutrition world is whether a low-carb keto diet can be used successfully by athletes. It’s practically written in stone that athletes need carbs to compete at a high level. However, if you take a closer look, things are not so cut and dry.
First, it’s important to remember that different sports have unique energy requirements. Distance running, cycling, and walking all rely predominantly on the oxidative energy system, whereas most team sports and popular fitness programs like CrossFit and high-intensity training have a fast glycolytic component. Then there is powerlifting, Olympic weight lifting, and strength training, which all rely predominantly on the ATP-PC energy system. All of the mentioned sports and activities have some overlap when it comes to how the body supplies energy to power them, but in general one energy system will dominate.
Once we know that there are different energy systems at work, it’s possible to see how carbohydrate needs and optimal nutrition vary depending on the sport in question. In the case of the ATP-PC system, which supplies energy “fast” energy for up to 15 seconds (and closer to 10 seconds), the body uses phosphocreatine to produce ATP—the energy source for the body.
In this case, the body needs high creatine muscle stores, which is the reason supplementing with creatine is recommended for sports that require short explosive bursts of power, including powerlifting and weight lifting. Sports that primarily utilize the ATP-PC energy system don’t burn as much glycogen as those that are glycolytic in nature and therefore may be more compatible with low-carb keto-style diets.
Sports that require you to work at a high-intensity for longer than 15 seconds also benefit from high creatine stores, but most important is a top notch anaerobic glycolytic system. This is where a higher carb intake is generally warranted. During anaerobic glycolysis, there is a lack of oxygen because your body is working at such an intense rate. This system provides energy for up to 110 seconds at which point work intensity slows and aerobic glycolysis takes over.
Carbohydrates in the form of glycogen and glucose are fuel during fast glycolysis, allowing the body to produce ATP at a rate of 1.0 to 2.0 mmoL/min. Examples of sports that require a significant contribution from the glycolytic energy system include CrossFit, team sports, interval training, and higher volume strength training (8 to 15 rep training for multiple sets).
Finally, there’s aerobic glycolysis—also known as the oxidative aerobic system—in which you are working at a lower intensity, generally for a longer duration. Your body is able to get enough oxygen to avoid the accumulation of lactate (from pyruvate) so that hydrogen ions don’t buildup in the muscle causing a drop in pH and the subsequent burning sensation that comes from prolonged intense efforts like sprints. With adequate oxygen, pyruvate turns into acetyl-coenzyme-A, entering the Krebs cycle to produce ATP.
Either carbohydrates or fat can provide energy during aerobic glycolysis. Fat is a slower burning fuel source than carbs. In response to a low-carb diet or fasting, the body will produce ketones from fat, which are then converted by the liver into acetyl-coenzyme-A. Acetyl-coenzyme-A enters the Krebs cycle to produce ATP just like pyruvate. This process takes longer than aerobic or anaerobic glycolysis, producing ATP at a rate of 0.4 mmoL/min compared to 1.0 to 2.0 mmoL/min.
This energy system predominates during rest, at lower exercise intensities such as walking, and endurance events. The oxidative aerobic system also kicks in during rest periods when weight training or breaks in play during team sports, such as during free throws in basketball or when the ball is at the other end of the field in soccer.
This information provides a framework for determining which sports a ketogenic diet can be used with. Powerlifting and Olympic weight lifting are good candidates because they typically rely on lower rep ranges and high intensities in which the ATP-PC system predominates. A well-functioning aerobic system is also necessary to ensure recovery between sets.
Early research suggests strength athletes can benefit from a ketogenic diet. A 2014 study found that elite Italian gymnasts who did a ketogenic diet for a month lost body fat and maintained muscle mass with no change in strength or gymnastic performance by the end of the study.
A newly published study found that trained male athletes who did a ketogenic diet for 10 weeks in conjunction with a training program that included both strength (4 sets of 1 to 5 reps) and hypertrophy (3 sets 8 to 15 reps) workouts significantly reduced body fat and improved lean mass and strength over the course of the study. Total testosterone increased, probably due to the high fat intake.
Finally, a third study found that when men and women ate a low-carb diet containing less than 50 grams of carbs a day, there was no negative effect on strength and power performance compared to a control group. This diet wasn’t a ketogenic diet per se because although carbs were low and fat was high, protein was higher than is typical of ketogenic diets. True ketogenic diets are very high in fat, providing upwards of 75 percent of calories, with protein providing closer to 10 to 15 percent, and carbs providing 5 percent.
The take away is that a ketogenic diet may be used in conjunction with powerlifting or other power-focused sports that derive a large portion of their energy from the ATP-PC system. Best results will generally come from the following strategies:
#1: Supplement with creatine. Taking 3 to 5 g a day will ensure you have optimal creatine stores in the muscle for powerful work.
#2: Don’t be afraid to go high in fat. People often just cut carbs without significantly increasing their fat intake. Or they replace carbs with protein instead of fat. This won’t facilitate the necessary metabolic adaptations for optimal success with a ketogenic diet.
#3: Allow for complete adaptation. Shifting from burning primarily carbs to running on ketones can be challenging as your body undergoes adaptations that allow it to make enzymes necessary for metabolizing ketones efficiently. This typically takes 1 to 2 weeks.
#4: Cycle carbs. Once you’ve got your body fat adapted (you’ve gone at least 14 days on the ketogenic diet), you may want to include periodic higher carb days to provide dietary variety and mental relief. Having a higher carb day once a week in which you consume carb foods around your training session can be beneficial.
#5: Eat real foods over processed foods. The ketogenic diet is so popular now that there are many processed ketogenic options available. You’ll get the best nutrition and have better overall results from focusing on whole foods in their most natural state.