DIFFERENCES IN ENERGY-EXPENDITURE AND SUBSTRATE OXIDATION BETWEEN HABITUAL HIGH-FAT AND LOW-FAT CONSUMERS (PHENOTYPES)

OBJECTIVE: To investigate physiological differences between habitual h igh-fat (HF) and low-fat (LF) consumers, which could influence the bal ance between energy expenditure and energy intake, and the potential f or weight gain. SUBJECTS: 16 young, lean males (eight HF and eight LF consumers; % energy from fat 44.3 and 32.0, respectively). MEASUREMENT S: Habitual dietary variables (from FFQ), body mass index (BMI), body fat % (measured by impedance), resting metabolic rate (RMR) (indirect calorimetry), substrate oxidation and basal heart rate, postprandial t hermogenesis and heart rate in response to a high-fat (low carbohydrat e (CHO)) and high-CHO (low fat) challenge. RESULTS: HF and LF (selecte d for their intake of fat) did not differ significantly in BMI or % bo dy fat. HF had a significantly higher RMR (1624 vs 1455 kcal/d) and ba sal heart rate (66 vs 57 bpm) than LF. Differences in oxygen utilisati on and heart rate were maintained over a 180 min period, following the high-fat and high-CHO challenge meals. HF had a significantly lower r esting respiratory quotient (RQ) than LF and the differences in averag e RO were significant over the 180 min examination period. HF had a si gnificantly lower RQ response to the high fat (low CHO) than to the hi gh CHO (low fat) challenge; this effect was not observed in LF. HF had higher total energy intake than LF and a higher absolute (but not %) intake of protein. CONCLUSION: Significant differences in basal energy expenditure and fat oxidation between habitual HF and LF consumers ha ve been observed. The contributions of energy intake and protein intak e (g not %) remain to be determined. In this particular group of subje cts (young adult males) a high energy intake characterised by a large fat component is associated with metabolic adaptations which could off set the weight inducing properties of a high-fat diet. These physiolog ical differences may be important when considering the relationship be tween dietary-fat and obesity.