A new study published in the American Journal of Clinical Nutrition tested 19 subjects on three different diets. Researchers measured appetite, caloric intake, body weight, and fat mass, as well as blood measurements for insulin, leptin (the hormone responsible for satiety) and ghrelin (the hunger hormone) during each of the phases.|
First, subjects followed a weight-maintenance diet of 15% protein, 35% fat, and 50% carbohydrate for two weeks.
Next, the subjects ate the same number of calories (an "isocaloric" diet), but with a different nutrient breakdown (30% protein, 20% fat, and 50% carbohydrate) for two weeks. This diet resulted in markedly increased satiety, although leptin levels did not change.
Finally, subjects followed an "ad libitum" diet (no caloric requirement or restriction), but were required to meet a specific nutrient breakdown of 30% protein, 20% fat, and 50% carbohydrate for 12 weeks. In this phase, participants spontaneously ate 376-504 fewer calories per day, and decreased both body weight and body fat. However, leptin levels decreased and ghrelin levels increased.
The researchers concluded that increasing protein intake from 15% to 30% of calories, with a constant carbohydrate intake, may be beneficial to weight loss.
This 30% protein, 50% carbohydrate diet fits into the healthy distribution range set by the Food and Nutrition Board, the Institute of Medicine, and National Academy of Sciences. It appears to benefit those trying to lose weight and body fat. The trouble is that many sources of protein are also high in fat. For healthy protein sources, select low-fat dairy products (milk, cheese and yogurt), egg whites or egg substitutes. To enjoy lean meats, trim off excess fat and remove skin. Select cooking methods that limit fat such as grilling, baking or broiling. Many plant proteins, such as tofu, beans, legumes and other soy products are naturally low in fat as well.