Ketone Bodies and Exercise Performance: The Next Magic Bullet or Merely Hype?
Elite athletes and coaches are in a constant search for training methods and nutritional strategies to support training and recovery efforts that may ultimately maximize athletes’ performance. Recently, there has been a re-emerging interest in the role of ketone bodies in exercise metabolism, with considerable media speculation about ketone body supplements being routinely used by professional cyclists.
Ketone bodies can serve as an important energy substrate under certain conditions, such as starvation, and can modulate carbohydrate and lipid metabolism. Dietary strategies to increase endogenous ketone body availability (i.e., a ketogenic diet) require a diet high in lipids and low in carbohydrates for ~4 days to induce nutritional ketosis. However, a high fat, low carbohydrate ketogenic diet may impair exercise performance via reducing the capacity to utilize carbohydrate, which forms a key fuel source for skeletal muscle during intense endurance-type exercise. Recently, ketone body supplements (ketone salts and esters) have emerged and may be used to rapidly increase ketone body availability, without the need to first adapt to a ketogenic diet.
However, the extent to which ketone bodies regulate skeletal muscle bioenergetics and substrate metabolism during prolonged endurance-type exercise of varying intensity and duration remains unknown. Therefore, at present there are no data available to suggest that ingestion of ketone bodies during exercise improves athletes’ performance under conditions where evidence-based nutritional strategies are applied appropriately.
Ketone bodies possess the ability to affect several physiological processes. Previously it has been proposed that ketone bodies can be utilized as an effective energy substrate under certain conditions. As such, ketone bodies have been suggested to have potential positive effects on exercise metabolism and performance. Serving as an alternative fuel source and sparing endogenous carbohydrate stores are among the proposed mechanisms by which ketone bodies have been suggested to benefit endurance exercise performance. Although ketone body supplementation has been proposed to be beneficial for endurance athletes and ketone esters are speculated to be routinely used by professional cyclists, to the best of our knowledge there is currently limited information on the effects of ketone body supplementation on exercise metabolism and performance in recreational and/or elite athletes.
Future research should focus on elucidating the metabolic effects of ketone body supplementation during exercise in athletes who adhere to appropriate nutrient intake strategies relevant for their respective sport and/or sports setting. Subsequently, many questions remain to be answered, including practical issues regarding the dose and timing of the proposed ketone (ester) supplement, the interaction with other substrates in various nutritional settings, and their quantitative contribution as an energy substrate during exercise of varying exercise intensity and duration. It will be important to evaluate the kinetics of ketone body availability in a sports-specific manner, tailored towards the needs of the individual athlete.
In conclusion, based upon the few available data and our current understanding of ketone body metabolism during exercise in a sports specific setting, we conclude there is currently no evidence to support the use of ketone bodies as an ergogenic aid under conditions where optimal evidence based nutritional strategies are applied.