A 27-yr-old woman with the myopathic form of acid maltase deficiency (AMD) developed severe respiratory insufficiency after a crash diet resulting in a 6-kg weight loss. While being maintained on home ventilation, an hypercaloric high-protein, low-carbohydrate diet (1800-2000 cal; 28% carbohydrates, 55% fat, 17% protein with 1.7 g protein/kg body weight) was instituted. This ameliorated her condition up to a level where useful life was possible and ventilation could be diminished.