In disagreement with a usual belief, women do not oxidize more fat at exercise than men, but their Lipoxmax occurs at a higher relative power intensity

Aims. - Several studies have shown that women, when they exercise at a given percentage of their aerobic capacity, oxidize more fat than men, thus saving their protein and glycogen stores. We wanted to characterize these differences in terms of levels of transition of balance of substrate oxidation and maximum lipid oxidation flow rate (MLOFR) during exercise. Methods. - Three groups (61 athletes, 196 sedentary and 47 type 2 diabetes mellitus [T2DM], in whom, men and women were matched for age, BMI and physical activity, performed a sub-maximal exercise test with four 6 min steady state steps for measurement of lipid and carbohydrate oxidation by indirect calorimetry. In all three groups MLOFRs are the same in both sexes (2 to 3 mg min(-1) kg(-1)), but among athletes and sedentary women have a curve of oxidation of lipids shifted to the right, a crossover point Of use Of substrates (PCX, the power for which energy comes mainly from carbohydrates) occurring at a 10-15% higher percentage of VO2max (p < 0.01). In DT2 this shift is no longer significant. The point of maximal lipid oxidation (Lipox(max)) also occurs at a higher percentage of VO2max (athletes: 44.27 +/- 15.97% theoretical VO2max versus 31.25 +/- 15.66% in men, p < 0.001; sedentary: 50.29 +/- 18.66% among women versus 36.75 +/- 15.22% in men, p <0.01; for T2DM these levels (42.8 +/- 2.4 to 39.8 +/- 3.7%) are not significantly different. Conclusion. - Gender-related differences are found on carefully matched subgroups, but are far to be major. They reflect a right shift by 10 to 15% of the curve of lipid oxidation as a function of VO2max, while rates of oxidation at the Lipox(max) do not differ between genders. In other words, women do not oxidize more lipids at exercise, but their ability to oxidize them reaches a maximum at a higher percentage of VO2max. This discrepancy seems to disappear in T2DM. (C) 2008 Publie par Elsevier Masson SAS.