One of the side effects of dieting can be losing muscle along with fat. Keeping muscle is important because these lean tissues help maintain healthy metabolism, physical activity, and blood sugar control.
In this study, 40 men and women, aged 35 to 65, with body mass index scores from 28 to 50, ate 750 fewer calories per day than their metabolism required. Starting three days before the low-calorie diet, each began taking 27 grams of whey protein, or 26 grams of soy protein, or 25 grams of maltodextrin as a placebo, all twice per day. After 14 days, those who took whey protein had much higher rates of muscle formation than either soy or placebo, suggesting that whey protein helps preserve muscle while dieting.