Objective:

To determine the role of macronutrients oxidation ability in the postprandial response to a high lipid load in the mechanisms conferring resistance or susceptibility to obesity.

Subjects and design:

Nine lean and nine obese young male subjects with habitual similar high-fat intake (> 40% of energy) and comparable physical activity were selected and categorized as ‘resistant’, those who remained lean (body mass index (BMI)< 25 kg/m 2), and ‘susceptible’, those who were obese (BMI> 30 kg/m 2). Fasting blood samples were taken for the evaluation of blood metabolic and hormonal variables. Resting metabolic rate (RMR) and substrates oxidation were measured by indirect calorimetry, in the fasting state and every 30 min for 3 h after a rich lipid meal (fat 94.7%) supplied to cover the 50% of the volunteers energy requirements. The study was performed at the Metabolic Unit of the University of Navarra.

Results:

Fasting RMR and lipid oxidation were higher in obese–susceptible subjects. However, similar values were found in both groups after adjustment for fat mass and free fat mass. The cumulative postprandial fat oxidation was also similar in both groups (despite having different tissue metabolic activity), whereas cumulative carbohydrate oxidation was lower in the obese–susceptible group. The thermic effect of food (% of dietary induced thermogenesis) was lower (P< 0.05) in the susceptible–obese subjects. The energy and fat balance were more positive in the obesity-susceptible individuals after the high fat load, who also showed higher fasting homeostatic model assessment index, low-density lipoprotein-cholesterol and triacylglyceride levels, hyperleptinemia and hypoadiponectinemia.

Conclusion:

Lean–resistant individuals came closer to achieving fat balance than obese–susceptible subjects. These metabolic and hormonal differences are probably genetically determined.