Objectives: Nutrition plays a key role for performance in endurance sports. Because the glucose stores of the body, i.e. muscle and liver glycogen, are limited, any preservation of glycogen stores and any alternative substrate to glucose can be useful for the physical performances. Some recent nutritional strategies aimed at increasing the availability of ketone bodies have been viewed with some enthusiasm. The aim of this review is to present the current state of knowledge on the interest that can be represented by ketogenic diets (RCet) or ketone dietary supplements (CC) on performance in endurance sports. News: RCet are poorly tolerated by athletes, which justifies the development of exogenous ketone supplements as ketone salts or ketone esters (ECC). ECCs provide good plasma availability of ß-hydroxybutyrate (ßHB), the main CC used by oxidation, with a dose effect; however, the CC oxidation remains highly dependent on glucose intake which must be reduced to a minimum. The ketone salts or ECC intakes increase the rate of CCs in the energy supply during exercise, which leads to a decrease in the glycolytic activity and glucose use. Given the well-known effects of CC on energy metabolism, some of these responses suggest that CCs may improve performance during single endurance exercises, and others tend to conclude the opposite. Ketone salts are now known to either alter or at the best not improve endurance performance. On the other hand, the currently available studies do not support positive effects of ECC for performance during endurance exercises. At best, ECCs could limit the fatigue induced by a training cycle of marked increased workload, but without improving performance in endurance exercises. Both ketone and ester salts are frequently at the origin of gut disorders that also are related to the dose ingested; in some studies, all the subjects presented gut disorders, of varying intensity, but which are always deleterious for endurance performances. Prospects and projects: The potential effects of CC on cognitive functions should be studied more precisely, with a potential interest in some sports such as team sports. The effects of CC on the epigenetic regulation of some genes important for the responses to endurance training should also be studied in further experiments.
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