Body composition, not dietary fatty acid composition, explains metabolic responses following a high-fat meal in premenopausal normal weight women: A single-blind randomized crossover study

The aim of this study was to examine the effect of three different fatty acid (FA)-rich meals enriched in either saturated (SFA), monounsaturated (MUFA), or polyunsaturated (PUFA) on postprandial metabolic responses in premenopausal, normal weight women. For this randomized, single-blind, crossover study three high-fat (HF) meals rich in either SFA, MUFA, or PUFA (65% energy from fat; 35% of participants’ total daily energy needs) were tested. For each visit, anthropometrics and resting metabolic rate were measured following a 12-15h fast. Then, participants consumed one of the HF meals and respiratory gases were collected using indirect calorimetry for 3h postprandially. Energy expenditure (EE) following a SFA-rich meal was a significantly higher than a MUFA-rich meal (p=0.04; η2 = .19) but SFA was not significantly different from PUFA. There was a trend towards significance in EE between PUFA and MUFA (p=0.06). After adjusting for fat-free mass (FFM), there were no longer condition or time effects for EE, although FFM remained a significant predictor (p=0.005; η2=.45). There were no significant differences between conditions for dietary induced thermogenesis (DIT) or substrate oxidation. A relationship between fat-mass (FM) and both total fat oxidation (r=.62; p=0.025) and total change in respiratory exchange ratio following a MUFA-rich meal, was observed (r=-.55; p=0.05). In conclusion, weight loss through increases in EE may be best achieved by increasing FFM rather than selection of FA type. Further, a relationship exists between FM and fat oxidation following a MUFA-rich meal, most likely due to an unidentified mechanism.