Maximal fat oxidation rate is higher in fit women and unfit women with obesity, compared to normal weight unfit women

INTRODUCTION: Maximal fat oxidation rate (MFO) is higher in aerobically fit vs. unfit young men, but this training related increase in MFO is attenuated in middle-aged men. Further, it has also been found that unfit men with obesity may have an elevated MFO compared to unfit normal-weight men.

AIM/HYPOTHESIS: Based hereupon, we aimed to investigate whether a fitness related higher MFO were attenuated in middle-aged women compared to young women. Also, we aimed to investigate if unfit women with obesity have a higher MFO compared to unfit normal-weight women. We hypothezised that the training related elevated MFO was attenuated in middle-aged women, but that unfit women with obesity would have an elevated MFO compared to unfit normal-weight women.

METHODS: We recruited a total of 70 women stratified into six groups: Young fit (n=12), young unfit (n=12) middle-aged fit (n=12), middle-aged unfit (n=12), unfit young women with obesity (n=12) and unfit middle-aged women with obesity (n=10). Body composition and resting blood samples were obtained and MFO was measured by a graded exercise test on a cycle ergometer via indirect calorimetry. Subsequently, a maximal exercise test was performed to establish V̇O2peak.

RESULTS: Young and middle-aged fit women had a higher MFO compared to age-matched unfit women, and young fit women had a higher MFO compared to fit middle-aged women. Unfit women with obesity, independent of age, had a higher MFO compared to their normal-weight and unfit counterparts.

CONCLUSION: The training related increase in MFO seems maintained in middle-aged women and secondly, we find that unfit women with obesity, independent of age have a higher MFO compared to unfit normal-weight women.