Being on a ketogenic diet while participating in endurance sports is becoming more popular as we continue to understand how a body uses ketones as a different food source. In the Body Reboot book we learn more about how a keto diet may affect physical performance, as well as what the diet is all about and how it can transform a life in a positive way. Even though this high fat, low carbohydrate diet within endurance sports is not fully understood, experts still like to weigh in (literally) with their opinion. Let’s see what some blogs and studies have shown so far about the keto diet within power sports.  

First, the Keto Diet App explains exactly what strength performance is below:

Strength performance includes events or sports that require muscular strength and power such as weight lifting, CrossFit and team games including rugby or American football.

They also go on to explain how important insulin is for strength training, and why many feel the keto diet isn’t a favorite diet to be on while focusing on endurance sports.

Due to carbohydrates being the biggest stimulator for insulin release, it is therefore believed that having a lack of carbohydrates in the diet will mean that the body cannot maintain or grow muscle mass.

However, insulin is a stimulator of protein synthesis only when adequate amino acids are available (amino acids are the building blocks of all tissues in the body), meaning that it is not only carbohydrates that can stimulate protein synthesis. Whilst ingestion of carbohydrates after exercise has been shown to stimulate protein synthesis, the effects are often very small and delayed in comparison to just consuming protein after exercise.

Some believe that a long-term keto diet can interfere with muscles, so for men and women who would like to maintain or grow a lot of muscles, the keto diet may not work. However, Exercise and Sport Sciences Reviews thinks otherwise:

The ketogenic diet (KD) is used widely as a weight loss strategy and, more rarely, as therapy for some diseases. In many sports, weight control is often necessary (boxing, weightlifting, wrestling, etc.), but the KD usually is not considered. Our hypothesis is that KD might be used to achieve fat loss without affecting strength/power performance negatively.

Evidence suggests that ketogenic diets can be used by athletes as a weight loss strategy without impairing strength performance, but more research is needed.

One discovery of the keto diet has been its ability to impact a person’s body composition potentially. One of the earlier studies from Original Research on the Annals of Internal Medicine showed that people lost body fat while still preserving lean body mass, despite the level of exercise they were doing in addition to endurance training.

Utilization of prolonged fasting as a means of weight reduction in obesity has been extensively evaluated and found to produce a consistent, adequate weight loss. Few reports have focused on the changes in gross body composition that accompany a period of fasting or compared such changes to those obtained with other dietary reducing programs. Although it is known that large losses of body potassium occur during the total fast this has not been correlated with lean body changes.

One of the first studies that did a study on the effects of the keto diet on strength performance used a group of gymnasts. The Int J Sports Exerc Med. study measured strength performance activities and body composition before the 30-day review and also after. During the 30 days, the athletes were on a modified ketogenic diet. After 30 days on the keto diet, the athletes resumed their usual diet (a standard American diet), and the results showed no significant difference between the keto diet and the American diet. Surprisingly enough the keto group increased in muscle mass while experiencing a reduction in body weight and fat mass. Check out the conclusion of the study:

To our knowledge, no research on the body composition and performance benefits of following a LCKD combined with CrossFit training has been conducted. With the current obesity epidemic overpowering our nation, Americans are constantly searching for the most effective diet protocol to induce weight and fat loss. Additionally, the constantly varied and competitive nature of CrossFit training has made it a popular exercise regimen for all levels of age and fitness.

Our data suggests that adhering to a LCKD can lead to weight loss and improved body composition outcomes without negatively affecting LBM, strength, or power performance. CrossFit athletes looking to explore novel nutritional approaches such as the low carbohydrate ketogenic diet may be able to improve performance while simultaneously improving body composition. These results could also be useful for weight category athletes, such as Olympic weightlifters, powerlifters, boxers, or wrestlers, seeking to lose a significant amount of body fat without compromising performance. Future research should be directed to the long term physiological adaptations which occur with a LCKD and CrossFit training, as well as the hormonal and psychological changes that may also transpire.

It’s likely that each person will have different body composition results while participating in strength performance activities. However, studies have shown for people who choose to do strength performance exercises regularly, it should be around 45 minutes for about 3-4 days a week. Strength and Conditioning Journal has more on this below:

For more than 3 decades, official recommendations have emphasized reduced total fat, saturated fat, and cholesterol intake as the primary method to achieve and maintain a healthy body weight. The best estimates of nutrient intake in the United States indicate that percent fat intake has declined over the past 3 decades, with a concomitant increase in carbohydrate intake. During the same time, obesity and diabetes rates have increased and heart disease remains the leading cause of death in most industrialized countries. The recent report of the massive trial in the Women's Health Initiative can only be described as discouraging with essentially no long-term effect on weight loss or cardiovascular disease (CVD) on a low-fat diet. In the area of weight loss, experiments continue to show that carbohydrate restriction is at least as effective as low-fat diets, usually more effective. In addition to weight loss, emerging research is showing that carbohydrate-restricted diets are an effective strategy to improve the metabolic syndrome (insulin resistance syndrome), which represents a group of seemingly disparate physiologic signs that indicate a predisposition to obesity, diabetes, and CVD. Consistent with the idea that an intolerance to carbohydrate (insulin resistance) is an underlying feature of the metabolic syndrome, research has shown that a reduction in dietary carbohydrate results in global improvement in traditional and emerging markers associated with this syndrome, particularly the cardiometabolic profile. Notably, these same results are found even when body weight does not change, demonstrating that there are underlying mechanisms contributing to these favorable results independent of the effects of weight loss.

The journal found that having a low carbohydrate diet may be better for overall strength training performance! They concluded their study by urging athletes to apply these practical applications:

Athletes who want to decrease body fat and improve body composition should pay particular attention to dietary carbohydrate intake. In practice, there are many ways to restrict carbohydrate. In our research studies, dietetic counseling was focused on lowering carbohydrate intake to approximately 10-15% of total energy, but this level of restriction may not be necessary. We have observed favorable effects on body composition when subjects were instructed to consume beef, poultry, fish, eggs, oils, and heavy cream; moderate amounts of hard cheeses, low-carbohydrate vegetables, and salad dressings; and small amounts of nuts, nut butters, and seeds. Subjects restricted fruit and fruit juices, dairy products (with the exception of heavy cream and hard cheese), breads, grains, pasta, cereal, high-carbohydrate vegetables, and desserts.

When carbohydrate restriction is combined with resistance training, body composition is further decreased, primarily because of positive effects on lean body mass. The ideal training program to elicit optimal changes in body composition remains unclear, but the program used in our work was a nonlinear approach alternating among heavy, moderate, and light days. Sessions were about 45 minutes in duration performed 3-4 days per week for 12 weeks and included a variety of exercises (Table 1). Training loads were determined using repetition maximum (RM) zones (e.g., 1-10 RM) and were progressively increased over the training period.

Based on everything we’ve seen from the above studies, there’s an increased interest to incorporate the keto diet within performance sports, but we still need more studies to look at this closer.

Some of the studies mentioned that a ketogenic diet combined with resistance training could result in better body composition, but there’s still a lack of understanding whether it would work long-term.

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Sources: Original Research/Annals of Internal Medicine, Keto Diet App, Int J Sports Exerc Med/ClinMed International Library, Strength and Conditioning Journal, Exercise and Sport Sciences Reviews