Background: Two single case studies suggest that a protein-rich diet may be beneficial for patients with McArdle disease, based on improvements in either endurance or muscle energetics, as assessed by phosphorous MR spectroscopy. In healthy subjects, proteins contribute very little to energy metabolism during exercise, which questions the effect of protein in McArdle disease.
Methods: In a crossover, open design, we studied seven patients with McArdle disease, who were randomised to follow either a carbohydrate- or protein-rich diet for 3 days before testing. Calorific intake on each diet was identical, and was adjusted to the subject's weight, age and sex. After each diet, exercise tolerance and maximal work capacity were tested on a bicycle ergometer, using a constant workload for 15 minutes followed by an incremental workload to exhaustion.
Results: During the constant workload, heart rate and perceived exertion were consistently lower (p<0.0005) on the carbohydrate- versus protein-rich diet. Patients also had a 25% improvement in maximal oxidative work capacity on the carbohydrate versus the protein diet.
Conclusions: This study shows that patients with McArdle disease can improve their maximal work capacity and exercise tolerance to submaximal workloads by maintaining a diet high in carbohydrate instead of protein. The carbohydrate diet not only improves tolerance to everyday activities, but will probably also help to prevent exercise-induced episodes of muscle injury in McArdle disease.