No Effect of Body Fat on Fat Oxidation Rates in Lean and Overweight Females When Aerobic Fitness is Controlled and Muscle Mass is Similar.

Fat oxidation (FATox) rates during exercise are largely determined by exercise intensity, aerobic fitness status, and body composition. FATox is proposed as a noninvasive means for assessing metabolic health in females. Overweight (OW) females rely less on fat than lean (LN) females during submaximal exercise although this remains unclear as previous studies have failed to control for aerobic fitness. This study compared FATox during submaximal exercise through indirect calorimetry between twenty female participants (N=20; mass: 63.1±9.0 kg; fat-free mass: 45.2±3.9 kg; fat mass: 17.8±6.0 kg; height: 165.0±5.7 cm; VO2peak: 35.8±2.9 mL·kg-1·min-1) of a similar VO2peak range (35±5 mL·kg-1·min-1), but stratified by bodyfat (BF%) into lean (LN) (N=10, ≤25 BF%) and overweight (OW) (N=10, ≥30 BF%). Participants exercised on a motorized treadmill for 3 min at 25%, 35%, 45%, and 55%, of their VO2peak. Absolute (g·min-1) and relative (mg·kgFFM-1·min-1) FATox rates were calculated from stoichiometric equations. There were no significant differences (p>0.05) at any stage for absolute, relative, or peak FATox rates between LN and OW females (absolute: LN: 0.30 ± 0.07 g·min-1 vs. OW: 0.32 ± 0.06 g·min-1). In conclusion, FATox rates during exercise were not different between LN and OW females with similar aerobic fitness levels. Coaches and practitioners can choose similar exercises that promote adherence and enjoyment while subsequently improving aerobic capacity in female participants.