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In a study of eight cyclists who took a ketone supplement before exercise, they increased their distance travelled by 2% during a 30-minute time trial. Although there was a lot of excitement about the results of this study, such improvements in athletic performance have not been replicated in most studies. A very recent meta-analysis of 13 controlled and randomized studies that compared the effects of a ketone salt or ester beverage to a placebo beverage on athletic performance concluded that ketone supplements had no significant effect on performance for sprints as well as exercises lasting up to 50 minutes. This negative finding could potentially be partly explained by the relative small sample sizes, the doses and the types of supplements used (salts versus esters), the types of efforts studied (duration and intensity of the exercise) and the presence of gastrointestinal disorders in the subjects, such as flatulence, nausea, diarrhea, constipation, vomiting and abdominal pain. Thus, the inability of many subjects to tolerate the supplements may have undone their performance-enhancing potential. The meta-analysis also suggests that studies are needed to specifically assess the effects of ketone supplements on performance in ultra-endurance exercise.
There is also evidence suggesting that ketone supplements may promote better recovery after exercise. A post-exercise state of ketosis is likely to promote both the recovery of glycogen stores in the body and muscular resynthesis, the two main goals of recovery. In post-exercise ketosis, the body burns ketones to produce energy, thereby saving the carbohydrates (necessary for glycogen) and proteins (necessary for muscles) for recovery. Thus, ingesting the usual amounts of carbohydrates and proteins recommended after exercise, in combination with a supplement of ketone esters, could help accelerate recovery.
In one study, 18 active men consumed either a ketone ester supplement or a placebo (up to three bottles per day) during a three-week intensive cycling training camp. During the third week of training, subjects who consumed the ketone supplement were able to perform 15% higher training length and perform at a 15% higher intensity as compared to the placebo group. In both groups, maximum heart rate during effort was reduced between the start and end of the training camp, but this decrease was significantly lower in subjects who consumed the ketone supplements, indicating that they were less fatigued and recovered better. The results of this study therefore suggest that consuming a ketone ester supplement could potentially be an effective strategy to prevent over-training and stimulate the body’s adaptation to endurance training.
In conclusion, although initial research and anecdotal evidence appear promising, there is still a lack of studies available to be able to confidently make recommendations for taking ketone supplements to improve sports performance.