RCT: Balance better than cyclical keto diet for athletic performance

By Nikki Hancocks

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getty | melnik

Related tags keto diet Sports nutrition Weight management athletes

A cyclical keto diet and a a nutritionally balanced diet are equally effective at reducing body weight but a balanced diet is better for improving anaerobic and strength performance, according to a recent RCT involving healthy young men.

Current trends in sports nutrition are increasingly reaching for the minimisation of carbs, with ketogenic diet becoming a very popular approach to improving physical fitness. The appeal of this diet is that reaching a ketogenic state allows an athlete to rely on stored fat as a source of fuel, due to increased fat burning capacity. This spares the more limited muscle glycogen stores, reducing the need to take on carbohydrates during competition.

According to current definitions, carbohydrate intake within the range of 50–150 g per day can be described as non-ketogenic low-carbohydrate regimens​. Ketogenic diet is most commonly defined by a daily carbohydrate intake below 50 g per day or energy provision from carbohydrates for up to 10% of total energy intake.

The cyclical ketogenic diet (CKD) alternates periods of ketogenic dieting with periods of high-carbohydrate consumption. The period of high-carbohydrate eating is supposed to refill muscle glycogen to sustain exercise performance​.

In order to compare the effect of a calorie-restricted cyclical ketogenic diet (CKD) versus nutritionally balanced diet (RD) on body composition, muscle strength, and endurance performance, a team of researchers from Prague performed an eight week RCT on healthy young males undergoing regular resistance and aerobic training. 

The team hypothesised that CKD would be more efficacious in inducing fat loss as, compared to RD, while maintaining aerobic performance.

Their reported results show that both the calorie-restricted ketogenic and nutritionally balanced diet lead to significant weight loss but weight lost via the balanced diet was due to fat loss, unlike the keto diet which was partly due to lean mass and water loss.   

The report states: "Despite comparable influence of both diets on body weight, we detected distinctions in their effects on body composition. In CKD group, the drop of body weight was due to a combination of decreased body fat, body water, and a slight, but significant, decline in lean body mass. On the contrary, in RD patients neither body water nor lean body mass were significantly affected and the weight reduction was predominantly due to body fat loss. 

"A slight decrease in lean body mass did not impair strength parameters as compared to baseline values. Nevertheless, we have noted that in RD patients both lat pull-down and leg-press significantly increased after eight weeks of intervention as compared to no change in subjects on CKD."

The team also noted an improvement in endurance performance in the RD group, compared to little or no improvement in the CKD group.

The reason behind the high water weight loss during a keto diet is when carb intake is restricted for a few days, glycogen stores in the muscle are reduced. Glycogen is responsible for water retention, so when its levels fall, so do our water levels.


Subjects were randomly assigned to follow either a CKD or RD (both with total caloric intake reduction by 500 kcal/day) while participating in three strength workouts and three aerobic workouts per week (30 min run, heart rate around 130–140 beats/min.) for eight weeks.

Total caloric intake reduction by 500 kcal/day is counted from balanced hypocaloric diet with a reduction of energy intake by 500 to 1000 kcal from the usual caloric intake. 

Those assigned the keto diet had a five day low-carb phase (carbohydrates up to 30 g; proteins 1.6 g/kg; fats: calculation of energy intake instead of carbohydrates) in order to induce and maintain ketosis. Following with two days of carbohydrate phase (weekends): nutrient ratio (carbohydrates 8–10 g/1 kg of non-fat tissue, 70% intake; proteins 15%; and fat 15%).

The strength development plan was designed to develop maximum strength in the tested exercise and the muscles involved. Three differently focused trainings per week were performed, focused on chest, legs, and back muscles. One training unit lasted approximately 60 min. For each training unit, the full focus was on the technique of execution and time under tension.

Each training unit was performed with the maximum possible effort to achieve the maximum results. The endurance test consisted of a 30-min run at constant heart rate (at approximately 70% max TF or around 130–140 heart beats/minute).The authors note the limitations of the current study include the relatively short duration, low number of subjects and inclusion of only male participants.

Previous research

The influence of keto diet combined with different forms of exercise on body composition has been studied both in athletes and in patients with obesity and other comorbidities on numerous occasions.

In some of the trials, isocaloric​ or hypocaloric ketogenic diet​ did not significantly change lean body mass while reducing body fat. On the contrary and in agreement with the current data, Perissious and colleagues found a reduction in lean body mass in patients with obesity undergoing exercise program while being on low carbohydrate diet​.

Differential effect of ketogenic vs. nutritionally balanced diet under hyperenergetic conditions has also been described in a study in healthy men undergoing an eight-week resistance training program. Under these conditions, lean body mass increased only in control diet while it was unaffected in the ketogenic diet group​.

Finally, ad libitum low carbohydrate ketogenic diet reduced body mass and lean body mass without compromising performance in powerlifting and Olympic weightlifting athletes​. 

In the current study, a slight decrease in lean body mass did not impair strength parameters as compared to baseline values. Nevertheless, authors noted that in RD patients both lat pull-down and leg-press significantly increased after eight weeks of intervention as compared to no change in subjects on CKD.

Source: Nutrients

Haluzik. M., et al

"The Influence of Cyclical Ketogenic Reduction Diet vs. Nutritionally Balanced Reduction Diet on Body Composition, Strength, and Endurance Performance in Healthy Young Males: A Randomized Controlled Trial"



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