AIM: The extent to which reduced insulin secretion during prolonged fasting reflects failure to compensate for whole-body insulin resistance or a normal adjustment to potentially increased hepatic insulin action is unknown. METHODS: We examined the effects of 36 versus 12 h fasting on insulin secretion and whole-body versus hepatic insulin action in 13 healthy young males. Hepatic glucose production and insulin action was studied using stable isotopes, whereas whole-body insulin action and insulin secretion was studied using an intravenous glucose tolerance test (IVGTT) and minimal modelling. Insulin, glucose and lipid profiles were subsequently measured during a refeeding meal-test. RESULTS: Prolonged fasting caused a minor reduction of first-phase insulin secretion in a context of improved hepatic insulin action contrasting an increase in whole-body insulin resistance. Accordingly, prolonged fasting was associated with opposite directed effects on hepatic versus whole-body insulin secretion disposition indices. Thirty-six compared with 12 h fasting was associated with increased plasma insulin levels during the refeeding meal test. CONCLUSION: In conclusion, reduced insulin secretion during prolonged fasting may represent a healthy response to improved hepatic insulin action. Use of insulin secretion disposition indices without taking organ specific insulin action into account may lead to erroneous conclusions.
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