Effects of modified sham feeding on ghrelin levels in healthy human subjects

Many hormonal and metabolic responses to nutrient intake begin during the cephalic or pre-absorptive phase and are mostly mediated by the autonomous nervous system. Ghrelin is a gut-brain hormone involved in the control of energy homeostasis with important orexigenic effects. The mechanisms involved in its preprandial rise and post-prandial fall are as yet unknown. The aim of the present study was to investigate the effects of the cephalic phase on ghrelin response to feeding in human subjects. The modified sham feeding (MSF), a well established technique in which nutrients are smelled, chewed, and tasted, but not swallowed, was used. Sixteen healthy volunteers were studied: 7 received a standardized mixed meal, and 9 underwent MSF. Several blood samples for ghrelin, insulin, glucose, PP were taken for 2h during both tests. Ghrelin levels significantly increased from -30 to 0 min before the 2 tests , then significantly decreased after both the real and the sham feeding, without significant differences being found by ANOVA. PP significantly increased also after MSF, while insulin and glucose levels were modified by the actual meal only. In conclusion, circulating ghrelin concentrations are decreased by sham feeding as they are by real feeding in humans. These findings underline the importance of the cephalic response to nutrient intake, and the role of vagal activity in the control of ghrelin secretion.