Scientific Study

OBJECTIVE: Dietary macronutrient proportions affect substrate utilization; but in practice people consume foods. We hypothesized that in overweight adults; a calorie controlled diet based on core foods and including walnuts may be advantageous in promoting greater use of fat stores. METHODS: This crossover study tested the effects of diet-related energy expenditure and fat oxidation in 16 overweight individuals over an 8-hour period. The 2 diets included breakfast and lunch meals during the measurement period and an evening meal the night before. They comprised core foods of bread/cereals; fruit; vegetables; milk/yogurt; and meat; and either walnuts (walnut diet) or olive oil (control diet). There was no difference in the energy and macronutrient composition of the diets in the measurement period. Energy expenditure; respiratory quotient (RQ); and macronutrient oxidation were assessed during two 8-hour stays in a room calorimeter facility. RESULTS: During the 8-hour measurement period; no difference in energy expenditure was noted between the diets; but a significant difference in RQ was observed between diets (control 0.908 +/- 0.046 vs. walnut 0.855 +/- 0.036; p = 0.029). Carbohydrate oxidation was lower and fat oxidation was higher during the walnut period than during the control period. CONCLUSIONS: A calorie controlled diet of core foods including walnuts may be advantageous in promoting the use of body fat stores; at least under acute conditions.