McArdle disease is a rare genetic condition that prevents the body from breaking down glycogen. Therefore, people with McArdle disease have a limited exercise capacity because, although they can burn glucose in the blood, they cannot break glycogen down into glucose so it can be used as a fuel. Consequently, providing an alternative fuel may improve the quality of life for people with McArdle disease.
Only two studies have examined the effect of exogenous ketones on exercise capacity in people with McArdle disease. A randomized crossover study by Valenzuela et al. found that ingesting a single dose of a ketone ester before an exercise test impaired maximal exercise capacity (lowered peak power output) compared to a placebo.[1] Neither the maximal heart rate nor the rating of perceived exertion (RPE) during this test were affected by the ketone ester.[1] Another randomized crossover study by Løkken et al. did not find an effect of a ketone ester on aerobic exercise metrics (e.g., heart rate and RPE) during submaximal exercise compared to a placebo.[2] Consequently, the current evidence does not support a beneficial effect of ketone supplementation on exercise capacity in people with McArdle disease.
Notably, the study by Valenzuela et al. also found that people with McArdle disease who ingested a carbohydrate-containing drink before the exercise test showed an increase in VO2max compared to a placebo.[1] Other studies confirm that carbohydrate supplementation before exercise[3][4] and a carbohydrate-rich diet[5][6] can improve exercise capacity in McArdle disease.