Regulation of muscle disuse atrophy by energy and protein intake in humans. Insights from bed rest studies

Physical inactivity and muscle atrophy are characte ristic features of many chronic disease states. Maintenance of neutral energy balance plays a pivotal role in counteracting inactivity-mediated decreases in muscle mass. Both overfeeding and underfeeding are associated with accelerated muscle loss. Inactivity is per se a low-grade pro-inflammatory condition and negatively interacts with excess ener gy intake to increase oxidative stress and muscle catabolism. Underfeeding and malnutrition are also frequently observed in patients with appetite abnormalities and anorexia. Inactivit y at negative energy balance accelerates muscle leucine oxidation and protein catabolism. Wi th regard to protein/amino acid intake, essential amino acid supplementation contributes to counteracting skeletal and myocardial muscle atrophy during inactivity. The rapidly dige sted whey protein was more efficient than the slowly digested casein in increasing postp randial protein anabolism during inactivity.