Objective: To explore the changes of ghrelin circulating levels induced by a mixed meal and their relationship with postprandial substrate oxidation rates in overweight and obese children with different levels of insulin sensitivity. Methods: A group of ten boys (age 9-12 years) with different levels of overweight (standard deviation score of body mass index: 1.6-3.2) was recruited. Body composition was measured by dual-energy X-ray absorptiometry. Insulin sensitivity was assessed by a frequently sampled i.v. glucose tolerance test. Pre-prandial and postprandial (3 h) substrate oxidation was measured by indirect calorimetry. The energy content of the test meal (16% protein, 36% carbohydrate and 48% fat) was 40% of pre-prandial energy expenditure (kJ/day). Results: Pre-prandial serum concentration of total ghrelin was 701.4±66.9 pg/ml (S.E.M.). The test meal induced a rapid decrease in ghrelin levels and maximal decrease was 27.3±2.7% below baseline. Meal intake induced a progressive increase of the carbohydrate oxidation rate for 45 min after food ingestion, followed by a slow decrease without returning to pre-prandial values. Postprandial cumulative carbohydrate oxidation was 16.9±0.8 g/3 h. Insulin sensitivity and postprandial maximal decrease of ghrelin concentration showed a significant correlation (r = 0.803, P < 0.01). Moreover, the postprandial carbohydrate oxidation rate correlated with the area under the curve for both insulin (r = 0.673, P < 0.03) and ghrelin (r = -0.661, P < 0.04). Conclusions: A relevant association between postprandial insulin-mediated glucose metabolism and ghrelin secretion in children with different levels of overweight was found. It is possible that the maintenance of an adequate level of insulin sensitivity and glucose oxidation may affect appetite regulation by favoring a more efficient postprandial ghrelin reduction.
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