Older men may not be eating enough beef. In a study of 35 men, all around 60 years old, it was found that bigger servings of beef – six ounces rather than the USDA's recommended three – helped most to slow muscle loss caused by lower testosterone, inactivity, and a diet too low in protein. "Men and women in their fifth decade of life begin to lose muscle mass," says lead author Stuart Phillips. "But you can almost reverse it by doing enough resistance training and eating enough protein." To test just how much protein is needed for aging men, researchers at the Exercise Metabolism Research Group at Canada's McMaster University gave five groups a weightlifting regimen and served them varying portions of lean ground beef. By measuring amino acids in the blood (needed to repair or form new muscle), they found that the biggest serving of beef was best for muscle synthesis.