SEATTLE--A high-protein diet lowered body weight in test subjects, possibly by suppressing appetite and spontaneous caloric intake, according to a study published in the American Journal of Clinical Nutrition (82, 1:41-48, 2005).
Researchers monitored appetite, caloric intake, body weight and fat mass in 19 subjects administered a weight-maintaining diet (15 percent protein, 35 percent fat and 50 percent carbohydrate), an isocaloric diet (30 percent protein, 20 percent fat and 50 percent carbohydrate) and an ad libitum diet (30 percent protein, 20 percent fat and 50 percent carbohydrate) for two-week periods for 12 weeks. At the conclusion of each diet phase, test subjects' blood was assayed for the area under the plasma concentration versus time curve (AUC) for insulin, leptin and ghrelin. The isocaloric, high-protein diet caused a significant increase in satiety, despite an unchanged leptin AUC, as well as a decrease in mean spontaneous energy intake (by 441 plus or minus 63 kcal/d), body weight (by 4.9 plus or minus 0.5 kg) and fat mass (by 3.7 plus or minus 0.4 kg), despite a significantly decreased leptin AUC and increased ghrelin AUC.
The researchers concluded an increase in dietary protein from 15 percent to 30 percent of energy at a constant carbohydrate intake produces a sustained decrease in ad libitum caloric intake, possibly mediated by increased central nervous system leptin sensitivity, and results in significant weight loss; they added the appetite-suppressing effect of protein may contribute to the weight loss produced by low-carbohydrate diets.
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