The Greater Contribution of Gluconeogenesis to Glucose Production in Obesity Is Related to Increased Whole-Body Protein Catabolism

Abstract

Obesity is associated with an increase in the fractional contribution of gluconeogenesis (GNG) to glucose production. We tested if this was related to the altered protein metabolism in obesity. GNG_PEP (via phosphoenol pyruvate [PEP]) was measured after a 17-h fast using the deuterated water method and ²H nuclear magnetic resonance spectroscopy of plasma glucose. Whole-body ¹³C-leucine and ³H-glucose kinetics were measured in the postabsorptive state and during a hyperinsulinemic-euglycemic-isoaminoacidemic clamp in 19 (10 men and 9 women) lean and 16 (7 men and 9 women) obese nondiabetic subjects. Endogenous glucose production was not different between groups. Postabsorptive %GNG_PEP and GNG_PEP flux were higher in obese subjects, and glycogenolysis contributed less to glucose production than in lean subjects. GNG_PEP flux correlated with all indexes of adiposity and with postabsorptive leucine rate of appearance (R_a) (protein catabolism). GNG_PEP was negatively related to the clamp glucose rate of disposal (R_d) and to the protein anabolic response to hyperinsulinemia. In conclusion, the increased contribution of GNG to glucose production in obesity is linked to increased postabsorptive protein catabolism and insulin resistance of both glucose and protein metabolism. Due to increased protein turnover rates, greater supply of gluconeogenic amino acids to the liver may trigger their preferential use over glycogen for glucose production.