Substrate utilization in female athletes: Implications for fuel selection and macronutrient requirements

Until recently, it was assumed that men and women responded similarly to the metabolic stress of exercise; however, accumulating evidence supports that sex (gender) influences fuel metabolism during exercise. Specifically, controlled studies accounting for menstrual cycle phase, diet, habitual training, and aerobic capacity have consistently shown that women have higher relative fat oxidation and lower protein and carbohydrate (CHO) oxidation during submaximal intensity exercise as compared to men (Tarnopolsky et al. 1990; Phillips et al. 1993; Tarnopolsky et al. 1995; Friedlander et al. 1998; Horton et al. 1998; Davis et al. 2000; Carter et al. 2001a; Lamont et al. 2001b; Ruby et al. 2002; Devries et al. 2005). Sex differences in metabolism are likely genetically regulated either by predetermined expression of genes or by the regulation of gene expression through cell signaling mechanisms, likely mediated through sex hormones (estrogen, progesterone, and testosterone) (Wolfe et al. 2000; Ferrando et al. 2002; Fu et al. 2009; Maher et al. 2009). Despite the differences in substrate utilization during exercise, the adaptations in aerobic capacity to endurance exercise training appear to be similar between men and women (Friedlander et al. 1998; McKenzie et al. 2000; Skinner et al. 2001).