Aging adults often experience changes in body composition resulting in weight loss due to a condition called sarcopenia. Sarcopenia is characterized by a decrease in lean muscle mass and a gain in fat mass.
The exact mechanisms involved in development of sarcopenia have not been defined but it is clear that there is an age-related increase in muscle breakdown and a decrease in muscle building after age 65. The causes could be decreased physical activity, decreased dietary protein intake, and increased insulin resistance. Resistance exercise is the most critical step to reducing sarcopenia, however increasing protein consumption paired with exercise is the only way to increase muscle mass.
In a study published by American Journal of Clinical Nutrition, muscle mass was tested in elderly men aged 65-70, who underwent specific resistance exercise paired with a protein diet from either all soy or all beef. At the end of a 12 week period, both groups gained mass and increased resting energy expenditure – there were no significant differences between the groups.
There was however a cholesterol increase in the all-beef group and no cholesterol increase in the all soy group – support of the clinical data showing that a diet low in fat and cholesterol and containing 25 grams of soy protein per day, may reduce heart disease…..
Effect of protein source on resistive-training-induced changes in body composition and muscle size in older men
Mark Haub, Amanda Wells, Mark Tarnopolsky, Wayne Campbell
American Journal of Clinical Nutrition 2002. 76: p. 511-517