Influence of dietary fat polyunsaturated to saturated ratio on energy substrate utilization in obesity.

The effect of the polyunsaturated to saturated (P:S) ratio of dietary fat on preprandial and postprandial macronutrient oxidation was studied in normal-weight and obese individuals. Total thermogenic response and fat and carbohydrate oxidation rates were determined by duplicate respiratory gas exchange measurements after test breakfasts, in seven normal and eight overweight subjects who consumed self-selected diets containing fat of high or low P:S ratio. Dietary intake records and erythrocyte linoleic to oleic (L:O) acid ratio changes were used as indicators of dietary compliance. No diet- or weight-related differences were observed in resting fat or carbohydrate oxidation rates, or in protein-free basal energy expenditure. Obese subjects consuming low P:S ratio diets exhibited reduced (P less than .05) contribution of fat oxidation to the thermogenic response, compared with lean individuals consuming high or low P:S ratio diets. However, total calories associated with the thermogenic response, and total fat and carbohydrate oxidation after the test breakfasts, did not differ significantly across groups. These findings suggest that, in obesity, whole-body postprandial disposal of dietary fat is influenced by the long-chain fatty acid composition.