Gluconeogenesis and energy expenditure after a high-protein, carbohydrate-free diet

Abstract

Background: High-protein diets have been shown to increase energy expenditure (EE). Objective: The objective was to study whether a high-protein, carbohydrate-free diet (H diet) increases gluconeogenesis and whether this can explain the increase in EE. Design: Ten healthy men with a mean (±SEM) body mass index (in kg/m2) of 23.0 ± 0.8 and age of 23 ± 1 y received an isoenergetic H diet (H condition; 30%, 0%, and 70% of energy from protein, carbohydrate, and fat, respectively) or a normal-protein diet (N condition; 12%, 55%, and 33% of energy from protein, carbohydrate, and fat, respectively) for 1.5 d according to a randomized crossover design, and EE was measured in a respiration chamber. Endogenous glucose production (EGP) and fractional gluconeogenesis were measured via infusion of [6,6-2H 2]glucose and ingestion of 2H2O; absolute gluconeogenesis was calculated by multiplying fractional gluconeogenesis by EGP. Body glycogen stores were lowered at the start of the intervention with an exhaustive glycogen-lowering exercise test. Results: EGP was lower in the H condition than in the N condition (181 ± 9 compared with 226 ± 9 g/d; P < 0.001), whereas fractional gluconeogenesis was higher (0.95 ± 0.04 compared with 0.64 ± 0.03; P < 0.001) and absolute gluconeogenesis tended to be higher (171 ± 10 compared with 145 ± 10 g/d; P = 0.06) in the H condition than in the N condition. EE (resting metabolic rate) was greater in the H condition than in the N condition (8.46 ± 0.23 compared with 8.12 ± 0.31 MJ/d; P < 0.05). The increase in EE was a function of the increase in gluconeogenesis (ΔEE = 0.007 x Δgluconeogenesis - 0.038; r = 0.70, R2 = 0.49, P < 0.05). The contribution of Δgluconeogenesis to ΔEE was 42%; the energy cost of gluconeogenesis was 33% (95% CI: 16%, 50%). Conclusions: Forty-two percent of the increase in energy expenditure after the H diet was explained by the increase in gluconeogenesis. The cost of gluconeogenesis was 33% of the energy content of the produced glucose. © 2009 American Society for Nutrition.