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HORMONES AND SIGNALING

Possible entrainment of ghrelin to habitual meal patterns in humans

Department of Foods and Nutrition, Purdue University, West Lafayette, Indiana

Submitted 11 October 2007 ; accepted in final form 7 January 2008

Ghrelin is reportedly a meal-initiation signal based on observations that concentrations increase before meals coincident with rising hunger. However, evidence that ghrelin peaks vary with feeding schedules suggests that it rises in anticipation of an expected meal, rather than eliciting feeding. To explore the entrainment of ghrelin profiles, this study investigated the association between varying habitual meal patterns and plasma ghrelin concentrations. Lean and obese adults following either a short intermeal interval (SII) pattern, with 2.5–3.5 h between their habitual breakfast and lunch times, or a long intermeal interval (LII) pattern, with 5.5–6.5 h between these eating occasions, participated. Food intake and appetite were recorded for 2 baseline days. On the subsequent test day, blood samples were collected over 8 h while participants ate a breakfast and lunch matched to their customary meals and pattern. Appetite ratings were obtained and ghrelin, insulin, glucose, and leptin concentrations were measured. Peak ghrelin concentrations differed significantly by group and occurred prior to each group's respective lunch time. Ghrelin concentrations directly correlated with subjective hunger. This association was stronger when hunger preceded ghrelin, a pattern inconsistent with ghrelin causing the hunger rise. Ghrelin concentrations were inversely correlated with insulin, and peak insulin concentrations preceded nadir ghrelin concentrations postprandially. Ghrelin concentrations periprandially, and over the entire test session, did not differ by meal group, likely because of similar intakes between groups. These data demonstrate that the timing of ghrelin peaks is related to habitual meal patterns and may rise in anticipation of eating rather than eliciting feeding.

hunger; appetite; food intake; satiety; gut hormone