Effects of fasting on insulin action and glucose kinetics in lean and obese men and women

Abstract

The development of insulin resistance in the obese individual could impair the ability to appropriately adjust metabolism to perturbations in energy balance. We investigated a 12- vs. 48-h fast on hepatic glucose production (R_a), peripheral glucose uptake (R_d), and skeletal muscle insulin signaling in lean and obese subjects. Healthy lean [ n = 14; age = 28.0 ± 1.4 yr; body mass index (BMI) = 22.8 ± 0.42] and nondiabetic obese ( n = 11; age = 34.6 ± 2.3 yr; BMI = 36.1 ± 1.5) subjects were studied following a 12- and 48-h fast during 2 h of rest and a 3-h 40 mU·m⁻²·min⁻¹hyperinsulinemic-euglycemic clamp (HEC). Basal glucose R_adecreased significantly from the 12- to 48-h fast (lean 1.96 ± 0.23 to 1.63 ± 0.15; obese 1.23 ± 0.07 to 1.07 ± 0.07 mg·kg⁻¹·min⁻¹; P = 0.004) and was equally suppressed during the HEC after both fasts. The increase in glucose R_dduring the HEC after the 12-h fast was significantly decreased in lean and obese subjects after the 48-h fast (lean 9.03 ± 1.17 to 4.16 ± 0.34, obese 6.10 ± 0.77 to 3.56 ± 0.30 mg·kg FFM⁻¹·min⁻¹; P < 0.001). After the 12- but not the 48-h fast, insulin-stimulated AKT Ser⁴⁷³phosphorylation was greater in lean than obese subjects. We conclude that 1) 48 h of fasting produces a marked decline in peripheral insulin action, while suppression of hepatic glucose production is maintained in lean and obese men and women; and 2) the magnitude of this decline is greater in lean vs. obese subjects.