Dietary macronutrient composition and its effect on 24-h substrate oxidation: A study of diurnal variations in...

In recent times, the complexity of food styles and meal content has increased, leading to significant variations in macronutrient composition between meals. This phenomenon has coincided with a rise in obesity rates. We aimed to determine whether a large variation in macronutrient composition between meals results in reduced fat oxidation.

A cross-over study was conducted with 13 healthy young men, using whole-body indirect calorimetry to test 24-h energy metabolic responses under three conditions: regular meals (R), high-carbohydrate breakfast (CB), or high-fat breakfast (FB), each with different macronutrient contents. The R condition included three meals daily with the same macronutrient composition. The CB condition included a high-carbohydrate meal at breakfast, high-fat meal at lunch, and high-carbohydrate meal at dinner. The FB condition included a high-fat meal at breakfast, high-carbohydrate meal at lunch, and high-carbohydrate meal at dinner. The daily macronutrient compositions were similar across the three conditions, except that CB and FB had larger variations in carbohydrate-fat balance between meals than R. The participants were tested in random order. During the dietary intervention, we compared 24-h whole-body metabolic parameters, including substrate oxidation (e.g., 24 h respiratory quotient [RQ]).

No significant differences were observed in the measures of energy expenditure among the three conditions. However, after adjusting for the sleeping RQ on a preceding day, the estimated 24hRQ was lower under the FB condition (0.845) than under the R (0.854, P = 0.0077 vs. FB) and CB conditions (0.853, P = 0.016 vs. FB). No difference was observed in the magnitude of the 5-h RQ change from lunch to dinner under the CB condition and in the magnitude of change from breakfast to lunch under the FB condition.

A large variation in the carbohydrate-fat balance between meals does not decrease daily fat oxidation. An FB may increase daily fat oxidation compared to a CB when the daily food quotient is constant, but this increase may not be owing to the upregulation of fat burning on a daily basis.