67 The Influence of Gender Differences in Metabolism upon Nutritional Recommendations for Athletes

There is accumulating evidence that males and females differ in the metabolic response to endurance exercise, with females showing a higher relative lipid oxidation, and a lower protein and carbohydrate oxidation at submaximal exercise intensifies. Interestingly, the aerobic capacity adaptations to endurance exercise training also appear to be qualitatively and quantitatively similar between the genders. In contrast, gender differences are apparent in the accumulation of muscle mass and strength following resistance exercise training; men show almost twice the response. Sex hormones are likely a major contributor to these gender differences. Estrogen has a mild anabolic effect and there is a decline in muscle mass in the early postmenopausal period that is attenuated with hormone replacement therapy (HRT). On the other hand, estrogen appears to have a significant effect on metabolic fuel selection during endurance exercise. Testosterone has a potent anabolic effect on muscle growth and supraphysiologic doses lead to significant strength and muscle mass gains, even in the absence of a resistance exercise-training program. The lower increase in amino acid oxidation seen in females during endurance exercise, suggests that any additional protein requirement for top sport female athletes would be lower than for their male counterparts. Females have an attenuated ability to increase muscle glycogen in response to an increase in the percentage of energy intake from dietary carbohydrate.