OBJECTIVE: Influences of gender and body weight on the hormonal response to eating are not well understood. This study was conducted to determine a convenient time-point to evaluate peak postprandial hormone responses and to test the hypothesis that gender and BMI interact to produce differences in postprandial secretion of selected humoral markers implicated in hunger and satiety. RESEARCH METHODS AND PROCEDURES: Fasting blood glucose, insulin, leptin, ghrelin, glucagon-like peptide-1, and glucagon were measured in normal-weight (20 or= 30 kg/m2) men (n = 9) and women (n = 11). A standard liquid meal was consumed, and humoral measurements were repeated every 10 minutes for 1 hour. Data were analyzed using repeated measures ANOVA with BMI and gender as main effects. RESULTS: Obese subjects had delayed peak insulin responses (p = 0.004), whereas obese men had a delayed nadir ghrelin response (p = 0.05). Obese subjects had higher and more sustained postprandial glucose (p = 0.02), and greater fasting (p = 0.0004) and postprandial insulin (p = 0.0001). Ghrelin decreased after the meal (p = 0.003); the percent change from fasting tended to be reduced in obese subjects (p = 0.07). Men had greater fasting (p = 0.02) and postprandial (p = 0.03) glucagon and a subtle postprandial decline in plasma leptin (p = 0.01). DISCUSSION: Peak hormone responses occurred 20 to 40 minutes after eating. Measurements made during this interval may be useful in evaluating postprandial response magnitude. Peak/nadir responses and time courses of postprandial responses are influenced by gender and BMI. Nutritional studies need to account for variability introduced by these factors.