Are High-Protein Diets Effective in McArdle's Disease?

To the Editor.  —Recent articles have held forth hope that certain metabolic myopathies might undergo improvement with proper dietary therapy.^1-3 In particular, the simple expedient of a high protein diet has appeared to be remarkably effective in the disparate disorders of McArdle's disease,¹ debrancher deficiency,₂ and acid maltase deficiency.³ With respect to McArdle's disease, a single patient, described by Slonim and Goans, demonstrated marked improvement after consuming a high protein diet.¹ Indeed, 45 minutes after a high protein (25% to 35%) meal, his exercise tolerance improved 400%. Over a 3-year period, the patient also experienced a decrease in muscular atrophy and an increase in exercise tolerance. The investigators discussed the possibility that increased availability of branched-chain amino acids (BCAAs) contributed to the improvement by serving as an alternative energy source for exercising muscle. To focus on this possibility, we studied the functional and metabolic muscle