Aim: Fat oxidation is impaired in obesity. The aim of this 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, glycemic 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 8 hours in 18 subjects. Results were compared using a repeated measures ANOVA with a customised post-hoc analysis (to compare the protein diets averaged versus control and to compare the low and high GI diets) and covariates in a linear model of the form; y=α + β1*fat free mass (kg)+β2*loge fat mass (kg).
Results:The full model found significant meal effects on fat oxidation (0.21±0.21kcal.min1 high protein high GI, 0.34±0.11kcal.min1 high protein low GI, 0.55±0.2kcal.min1 control, F=3.50, P=0.007). The effect on energy expenditure (1.67±0.07kcal.min1 high protein high GI, 1.61±0.08kcal.min1 high protein low GI, 1.67±0.08kcal.min1 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 meal response was influenced by body composition. The high protein meals eliminated the negative relationship between body fat and fat oxidation (α= -4.7, β2=2.23, P
Conclusion: High protein intakes may ameliorate an obesity induced decline in fat oxidation.