The ketogenic diet (KD), characterized by a significant reduction in carbohydrate consumption and a corresponding increase in dietary fat, has been investigated for its effects on body composition in various populations. More recently, some have recommended that athletes adhere to ketogenic diets in order to optimize changes in body composition during training. While KD has been shown to have positive effects on body mass reduction in obese subjects and potential benefits in managing neurological diseases and certain types of cancer, its impact on physical performance, particularly in conjunction with strength training, warrants careful examination. This article explores the benefits and considerations of combining a keto diet with strength training, drawing on scientific evidence and expert opinions.
Understanding the Ketogenic Diet
A KD is based on a marked reduction in carbohydrate consumption (i.e., ≈50 g per day or 10% of total daily caloric intake) and a corresponding increase in dietary fat (≈ 60-80% of total calories) and protein consumption (i.e., ≈ 1.2-1.5 g·kg− 1·d− 1). This macronutrient distribution leads to an increase in the production of ketone bodies (KB), such as acetoacetate, β-hydroxybutyrate and acetone, and consequently to the state of physiological ketosis (i.e., KB blood levels between 7 and 8 mM and blood pH of ≈7.4). The increase in KB and the subsequent physiological adaptations after following a KD not only have shown positive effects in the reduction of body mass (BM) in obese subjects, but also the reduction in blood concentrations of low-density lipoprotein cholesterol, triacylglycerols and glucose while an increase in high-density lipoprotein cholesterol has been reported. Similarly, there is evidence of the benefits of KDs in the treatment or management of neurological diseases such as epilepsy and certain types of cancer. Therefore, adherence to a KD can be considered part of the therapeutic management of these pathologies.
Potential Benefits of Keto Diet for Strength Training
Fat Loss
One of the primary benefits of a KD is its ability to promote fat loss. Research suggests that KDs can be effective for reducing total body and fat mass compared with non-KDs. A significant reduction in fat mass was observed in KD (− 1.1 ± 1.5 kg; P = 0.042; d = − 0.2) but not in NDK (0.3 ± 0.8 kg; P = 0.225; d = 0.1). This can be particularly appealing to athletes in weight-category sports or those aiming to minimize body fat during the "cutting phase." Studies have demonstrated that individuals on a KD experience greater body fat loss than those on high-carb diets.
Muscle Mass Maintenance
Contrary to the misconception that KDs lead to muscle loss, studies suggest that they can help preserve muscle mass during training. In one study, elite gymnasts who adopted a KD while maintaining their training routines experienced no change in muscle mass but significantly reduced body fat. Similarly, athletes in a CrossFit program who followed a KD for six weeks showed no significant change in muscle mass while reducing weight and body fat.
Increased Fat Burning
As the body becomes "keto-adapted," it trains itself to burn fat for energy instead of carbohydrates. This can lead to a greater ability to utilize fat from food and body storage areas, ultimately improving body composition. A study of elite competitive walkers showed that those on KDs significantly increased fat burning during training compared to those on a standard diet.
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Potential for Increased Testosterone
Research indicates that a KD may lead to a greater increase in testosterone levels. This suggests that when combined with strength training, a KD is perfectly adequate for increasing body weight, most of which is lean muscle.
Considerations and Potential Drawbacks
Impact on High-Intensity Exercise
The majority of high-intensity exercise, such as strength training and sprinting, is powered by carbohydrates. On a KD, the body burns fat for energy, which is a less efficient process than burning carbohydrates. This can limit performance during high-intensity workouts. One study found that participants on a KD experienced a drop in endurance capacity and peak power.
Reduced Glycogen Stores
Glycogen, the stored form of glucose in muscles, is crucial for energy availability during exercise. Some argue that low glycogen stores on a KD could compromise energy and limit performance. However, studies have shown that keto-adapted athletes can maintain similar levels of stored muscle glycogen as athletes consuming high amounts of carbohydrates.
Keto Flu
When starting a KD, individuals may experience the "keto flu," a set of symptoms including headaches, fatigue, and difficulty sleeping. This occurs as the body transitions from relying on sugar to eliminating it.
Bone Health
There can be issues with bone health when people switch to low carbohydrate ketogenic diets. We see that markers for bone breakdown are higher and markers for bone building are lower. This is a common side effect in kids who are fed a ketogenic diet to treat epilepsy.
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Strategies to Mitigate Potential Drawbacks
Adequate Protein Intake
To counter the potential for muscle loss, it is crucial to consume adequate protein while on a KD. Aim for a protein intake higher than the current recommendation of 1.7 g∙kg− 1·d− 1.
Cyclical Ketogenic Diet
Consider a cyclical KD, which involves alternating between periods of KD and periods of carbohydrate reintroduction. This may help replenish glycogen stores and improve performance during high-intensity exercise.
Exogenous Ketone Supplements
Some studies suggest that ketone esters, a type of ketone supplement, may improve brain function and potentially preserve muscle mass. However, more research is needed in this area.
Scientific Evidence and Research Studies
Several studies have investigated the effects of KD on body composition and strength levels in resistance-trained subjects.
Study on Trained Women
One study evaluated the effect of a KD on body composition and strength in trained women following an eight-week resistance training program. The results showed a significant reduction in fat mass in the KD group but no significant changes in fat-free mass. While no significant changes in bench press were observed, significant changes were noted in squat and countermovement jump.
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Study on Resistance Exercise and Ketogenic Diet
Another study assigned untrained women between 20 and 40 years with BMI ≥ 25 kg*m-2 into either an exercise group or a low-carbohydrate plus exercise group. Both groups performed 60-100 min of varied resistance exercise twice weekly. The low-carbohydrate plus exercise group lost 5.6 ± 2.6 kg of body weight and 5.6 ± 2.9 kg of fat mass with no significant change in lean body mass, while the exercise group gained 1.6 ± 1.8 kg of lean body mass with no significant change in fat mass.
Studies on Muscle Mass and Strength
Research has shown that athletes who adopt a keto diet experience greater body fat loss than a group of high-carb dieters. After 8 weeks of a keto-diet and resistance training program, young men experienced reductions in fat mass and visceral adipose tissue-changes that weren’t seen in the non-keto groups.
Expert Opinions
Andy Galpin, PhD, a professor of kinesiology at California State University in Fullerton, states that there is very little evidence that the ketogenic diet is better for anything exercise-wise. He adds that it’s not going to be any better for physical performance than the standard diet.
UC Davis molecular exercise physiologist Keith Baar notes that a keto diet prevents muscle deterioration and even restores muscle function. However, he cautions that the ketogenic diet slows the maximal rate of energy production, which can be a curse for athletes.