Appetite Responds to Changes in Meal Content, Whereas Ghrelin, Leptin, and Insulin Track Changes in Energy Availability

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Abstract
Context: It is uncertain how between-meal variations in energy availability and physiological changes in ghrelin, leptin, and insulin affect appetite. Objective: The aim of the study was to examine the influence on human appetite of the meal size and its nutrient content or changes in energy availability and concentrations of ghrelin, leptin, and insulin. Design: We conducted a crossover study manipulating meal size and energy availability through exercise energy expenditure and iv nutrient replacement (TPN). Setting: The study was performed at a Clinical Research Center. Participants: Ten healthy postmenopausal women (age, 59.7 ± 1.5 yr; mean body mass index, 26 kg/m2) were studied. Interventions: We conducted trials based on different morning meal size (418 vs. 2090 KJ), presence or absence of exercise energy expenditure (2273 to 2361 KJ), energy replacement by TPN (1521 to 1538 KJ), and a midday ad libitum meal. Main Outcome Measures: Changes in hunger, fullness, midday ad libitum food consumption, and concentrations of ghrelin, leptin, insulin, and metabolic fuels were measured. We also performed midday meal tests for the presence of caloric compensation. Results: Appetite was influenced by the size and energy content of the meals, but not by variation in energy availability which also did not trigger consummatory compensation. Exercise reduced hunger and increased fullness. Ghrelin, leptin, and insulin responded to changes in energy availability but not to meal size. Appetite was unaffected by physiological changes in ghrelin, leptin, or insulin. Conclusions: During rest, appetite is influenced by the size and energy content of meals, but it bears no homeostatic relationship to between-meal changes in energy availability due to small meals, exercise, or TPN, or concentrations of ghrelin, leptin, and insulin.

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