Standard light breakfast inhibits circulating ghrelin level to the same extent of oral glucose load in humans, despite different impact on glucose and insulin levels

Ghrelin levels are increased by fasting and energy restriction, decreased by food intake, glucose load and insulin but not by lipids and amino acids. Accordingly, ghrelin levels are elevated in anorexia and cachexia and reduced in obesity. Herein we compared the effects of a standardized light breakfast (SLB) on morning circulating ghrelin levels with those of oral glucose load (OGTT) in normal subjects. Specifically, 8 young adult volunteers [age (mean±SEM): 28.0±2.0 yr; body mass index (BMI): 22.4±0.6 kg/m2] underwent the following testing sessions: a) OGTT (100 g po at 0 min, about 400 kcal); b) SLB (about 400 kcal, 45% carbohydrates, 13% proteins and 42% lipids at 0 min) on three different days; c) placebo (100 ml water po). In all sessions, at baseline, blood samples were withdrawn twice at 5-min interval to characterize the inter- and intra-individual reproducibility of the variables assayed. After placebo and OGTT, blood samples were withdrawn every 15 min up to +120 min. After SLB, blood samples were taken at 60 min only. Ghrelin, insulin and glucose levels were assayed at each time point in all sessions. Similarly to insulin and glucose levels, at baseline, ghrelin showed remarkable intra-subject reproducibility both in the same sessions and among the different sessions. Placebo did not significantly modify ghrelin, insulin and glucose. OGTT increased (p<0.01) glucose (baseline vs peak: 80.0±3.6 vs 140.5±6.3 mg/dl) and insulin (20.2±6.2 vs 115.3±10.3 mU/l) levels. SLB increased (p<0.05) both insulin (16.3±1.8 vs 48.3±6.3 mU/l) and glucose (74.5±3.7 vs 82.9±3.1 mg/dl) levels. Notably both the insulin and glucose increases after OGTT were significantly higher (p<0.01) than that induced by SLB. After OGTT, ghrelin levels underwent a significant reduction (baseline vs nadir: 355.7±150.8 vs 243.3±98.8 pg/ml; p<0.05) reaching the nadir at time +60 min. Similarly, ghrelin levels 60 min after SLB (264.8±44.8 pg/ml were significantly (p<0.01) lower than at baseline (341.4±54.9 pg/ml). No significant differences in the reduction of ghrelin levels after OGTT and SLB were observed. In conclusion, these findings show that light breakfast inhibits ghrelin secretion to the same extent of OGTT in adults despite lower variations in glucose and insulin levels