Substrate Utilization Differences Between Overweight And Obese Men And Women During Exercise

Abstract

As exercise intensity and duration increase, substrate utilization typically shifts to carbohydrates over fats. However, individuals with higher levels of adiposity have been shown to rely more heavily on fat oxidation during higher intensity exercise than their lean counterparts. Currently, there is limited research on how carbohydrate and fat oxidation differ in men compared to women at different exercise intensities. PURPOSE: To examine the difference in substrate utilization of fat and carbohydrate between men and women at different exercise intensities. METHODS: Participants (n=34) between 18-55 years old (Women: 35.9 +/- 11.3 years; Men: 36.1 +/- 7.7 years) with a BMI between 27-35 kg/m2 (Women: 30.5 +/- 1.7 kg/m2; Men: 30.6 +/- 2.2 kg/m2) completed a modified Bruce protocol on a treadmill for measurement of a estimated VO2Max at their age-predicted heart rate max. To be included in the analysis these participants were required to reach 85% age predicted heart rate max. RESULTS: Women utilized a higher (p≤0.05) percentage of fat at 65% (Women: 42.9 ± 16.9%; Men: 24.8 ± 17.7%), and 80% (Women: 14.7 ± 18.2%; Men: 2.7 ± 7.95%) of their VO2Max and greater (p≤0.05) usage of overall Kcal from fat per kg of body mass at 80% (Women: 0.02 ± 0.02kcalF/kg; Men: 0.01 ± 0.01 kcalF/kg) of VO2Max. Men relied more heavily (p≤0.05) than women on carbohydrates per kg of body mass at 50% (Women: 0.03 ± 0.02kcalC/kg; Men: 0.06 ± 0.03kcalC/kg), 65% (Women: 0.07 ± 0.03kcalC/kg; Men: 0.13 ± 0.06kcalC/kg) and 80% (Women: 0.16 ± 0.08kcalC/kg; Men: 0.26 ± 0.08kcalC/kg) of VO2max. CONCLUSIONS: Women oxidized more fat than men at 65% and 80% VO2Max, but not 35% and 50% VO2Max. As exercise intensity increased, the gap between women and men fat oxidation levels became larger. Funding: Montana State University Research Initiative 51040-MUSRI2015-03 and USDA-NIFA 2017-67018-26367.