KETOGENIC DIETS: EFFECTS ON PERFORMANCE AND BODY COMPOSITION

Among the multitude of diets that have gained great popularity in recent years in the world of sports, ketogenic diets are most likely at the top. Ketogenic diets are characterized by providing a low amount of carbohydrates (normally <50 grams per day), for which fat or protein intake usually increases (which should in all cases meet the minimum recommendations of 0.8-1.2 g/kg/day). The reasons why athletes turn to this diet are very diverse, including everything from a possible improvement in performance to weight loss or improvement in body composition. But what does science really say about its effectiveness?

Endurance sports

There is some physiological basis for thinking that ketogenic diets could “get the body used to it” and decrease dependence on carbohydrates, thus increasing the ability to oxidize fat during exercise. These adaptations would be potentially beneficial especially for endurance athletes since, as we have commented in previousarticles, although carbohydrates are the main source of energy (especially at high intensities)1Their stores (i.e. glycogen) can be depleted leading to fatigue. 

In this sense, there is evidence that shows that low-carbohydrate or ketogenic diets increase fat oxidation and decrease carbohydrate utilization, especially during low-intensity exercise.2These results may be promising for endurance athletes, and in fact a study conducted on cyclists produced some interesting results.3In that study, some of the participants began following a ketogenic diet (6% carbohydrates) for 12 weeks, while others maintained a high-carbohydrate diet (65% carbohydrates).3The results showed that the ketogenic diet not only increased fat oxidation during a 100 km bike test, but also increased performance in a test carried out at the end of those 100 km.3However, despite these “preliminary” results, numerous subsequent studies have found no such benefits, and in fact a recent systematic review that included 17 studies concluded that ketogenic diets are not beneficial for endurance performance.4For example, studies led by researcher Louise Burke have repeatedly shown in elite-level endurance athletes that following a ketogenic diet for 3 weeks results in worse performance and economy of effort at competition intensities, despite increasing fat oxidation.5,6 

Strength sports

Ketogenic diets have also made a strong splash in sports where strength or power prevails, such as CrossFit. Given the importance of carbohydrates in exercises performed at high intensity, in these sports it may be more expected that reducing their availability in the diet will result in detrimental results. In this sense, in the aforementioned systematic review it was observed that, of the 16 measurements available for strength or power, only in 2 were benefits of ketogenic diets observed, while in the others no benefits or negative effects were seen.4

Body composition

Although it may not have direct performance benefits, many athletes (both endurance and strength) turn to ketogenic diets for their possible benefits on weight loss and body composition. In this sense, a meta-analysis was recently published that evaluated 13 studies that analyzed the effects of ketogenic diets together with strength training on body composition.7The results showed that, compared to a non-ketogenic diet, the ketogenic diet significantly decreased body weight (3.7 kg on average) and fat mass (2.2 kg on average), but also muscle mass (-1.3 kg) despite the participants doing strength training. These results are confirmed in a recent study carried out on bodybuilders that observed that, although the ketogenic diet was associated with greater fat loss than a “normal” diet, only those who followed the normal diet increased their muscle mass. However, both groups improved their strength similarly.8

Conclusions

Current evidence does not support the benefits of ketogenic diets on strength or endurance performance (although more studies are needed in ultra-endurance sports). On the other hand, there is evidence that supports the benefits of these diets for losing weight and fat. However, it is important to keep in mind that they can also result in greater loss of muscle mass (or less benefits if combined with strength training), so it will be essential to control protein consumption. 

AUTHOR

Pedro Valenzuela
Researcher in the Physiology Unit of the University of Alcalá and in the Performance Control Unit at the Sports Medicine Center (AEPSAD, CAR of Madrid).
Web: www.fissac.com

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References

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3. McSwiney FT, Wardrop B, Hyde PN, Lafountain RA, Volek JS, Doyle L. Keto-adaptation enhances exercise performance and body composition responses to training in endurance athletes. Metabolism. 2018;81:25-34. doi:10.1016/j.metabol.2017.11.016
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5. Burke LM, Ross ML, Garvican-Lewis LA, et al. Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. J Physiol. 2017;595(9):2785-2807. doi:10.1113/JP273230
6. Burke LM, Sharma AP, Heikura IA, et al. Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic Low Carbohydrate, High Fat (LCHF) diet is reproducibleitle. PLoS One. 2020;(Ahead of Print):1-31. doi:10.1371/journal.pone.0234027
7. Ashtary-Larky D, Bagheri R, Asbaghi O, Tinsley G, Kooti W. Effects of resistance training combined with a ketogenic diet on body composition: a systematic review and meta-analysis. Crit Rev Food Sci Nutr. 2021;In press.
8. Paoli A, Cenci L, Pompei PL, et al. Effects of two months of very low carbohydrate ketogenic diet on body composition, muscle strength, muscle area, and blood parameters in competitive natural body builders. Nutrients. 2021;13(2):1-14. doi:10.3390/nu13020374