An increase in dietary protein from 15% to 30% of energy at a constant carbohydrate intake produces a sustained decrease in ad libitum caloric intake that may be mediated by increased central nervous system leptin sensitivity and results in significant weight loss. This anorexic effect of protein may contribute to the weight loss produced by low-carbohydrate diets.

An increase in dietary protein from 15% to 30% of energy at a constant carbohydrate intake produces a sustained decrease in ad libitum caloric intake that may be mediated by increased central nervous system leptin sensitivity and results in significant weight loss. This anorexic effect of protein may contribute to the weight loss produced by low-carbohydrate diets.

These findings suggest possible mechanisms contributing to the effects of high-protein/low-carbohydrate diets to promote weight loss, and high-fat diets to promote weight gain.

Plasma ghrelin levels rise before meals and fall rapidly afterward. If ghrelin is a physiological meal-initiation signal, then a large oral caloric load should suppress ghrelin levels more than a small caloric load, and the request for a subsequent meal should be predicted by recovery of the plasma ghrelin level. To test this hypothesis, 10 volunteers were given, at three separate sessions, liquid meals (preloads) with widely varied caloric content (7.5%, 16%, or 33% of total daily energy expenditure) but equivalent volume. Preloads were consumed at 0900 h, and blood was sampled every 20 min from 0800 h until 80 min after subjects spontaneously requested a meal. The mean (+/- SE) intervals between ingestion of the 7.5%, 16%, and 33% preloads and the subsequent voluntary meal requests were 247 +/- 24, 286 +/- 20, and 321 +/- 27 min, respectively (P = 0.015), and the nadir plasma ghrelin levels were 80.2 +/- 2.8%, 72.7 +/- 2.7%, and 60.8 +/- 2.7% of baseline (the 0900 h value), respectively (P < 0.001). A Cox regression analysis failed to show a relationship between ghrelin profile and the spontaneous meal request. We conclude that the depth of postprandial ghrelin suppression is proportional to ingested caloric load but that recovery of plasma ghrelin is not a critical determinant of intermeal interval.