High-protein meals may benefit fat oxidation and energy expenditure in individuals with higher body fat

Aim: Fat oxidation is impaired in obesity. The aim of the present study was to determine if fat oxidation, seen in a high-protein meal response, was influenced by body composition.

Methods: Subjects were provided with control (14% protein, glycaemic index, GI 65), high-protein high-GI (33% protein, GI 74) and high-protein low-GI (35% protein, GI 45) meals. Substrate oxidation and energy expenditure were measured in room calorimeters over eight hours in 18 subjects. Results were compared using a repeated-measures anova with a customised post-hoc analysis (to compare the protein diets averaged vs control and to compare the low- and high-GI diets) and covariates in a linear model of the form: y = ñ + ò1 àfat-free mass (kg) + ò2 àloge fat mass (kg).

Results: The full model found significant meal effects on fat oxidation (0.21 ñ 0.21 kcal/minute high-protein high-GI, 0.34 ñ 0.11 kcal/minute high-protein low-GI, 0.55 ñ 0.2 kcal/minute control, F = 3.50, P = 0.007). The effect on energy expenditure (1.67 ñ 0.07 kcal/minute high-protein high-GI, 1.61 ñ 0.08 kcal/minute high-protein low-GI, 1.67 ñ 0.08 kcal/minute control) approached significance (F = 2.45, P = 0.070). Post-hoc analysis revealed a protein effect (P = 0.004 for fat oxidation and P = 0.030 for energy expenditure). Significant interactions indicated that meal response was influenced by body composition. The high-protein meals eliminated the negative relationship between body fat and fat oxidation (ñ = 4.7, ò2 = 2.23, P < 0.01) and between body fat and energy expenditure, which were evident in the control meal (ñ = 1.5, ò2 = 0.63, P < 0.05). No effect of GI was evident.

Conclusion: High-protein intakes may ameliorate an obesity-induced decline in fat oxidation.