Endocrine Effects of Food Intake: Insulin, Ghrelin, and Leptin Responses to a Single Bolus of Essential Amino Acids in Humans

Abstract

Background: This study deals with the physiological effects of an oral bolus of essential amino acids (AA) on the secretion of insulin, ghrelin and leptin in fasting humans. Methods: 12 healthy adults (age 18–40 years, 10 males, 2 females, body mass index 18.0–23.5 kg/m²) were included in our study. Seven fasted volunteers consumed an AA mixture (0.35 g/kg BW), 5 served as controls. Serum AA, glucose, albumin, urea and hormones were measured at 0, 15, 30 min and thereafter at 30-min intervals up to 5 h. Results: Glucose, albumin and urea remained constant, peak AA concentrations were achieved at 30 min for methionine (Met), at 60 min for all other AA. The insulin peak (533% compared to basal level, p < 0.01) at 30 min was earlier than the peaks of all AA except for Met. Ghrelin showed a continuous rise towards the end of the experiment leading to a 3-fold increase in initial concentrations in the study group (p < 0.001), significantly higher than in the control group (p < 0.05). In contrast, both groups exhibited almost constant leptin concentrations. Conclusion: Our data indicate that an oral low-dose AA bolus not only causes considerable hyperaminoacidemia and hyperinsulinemia but is also accompanied by an increased ghrelin secretion in fasted humans. This may be a specific effect or may be due to the fact that a single bolus of AA is not a sufficient stimulus to induce satiety. Leptin, however, is not a key mediator in this setting.