Gender differences in leucine, but not lysine, kinetics

There is a controversy in the literature as to the effects of gender on leu cine kinetics. Two research groups found that men oxidize more leucine duri ng exercise, whereas another group showed no gender effects. The purpose of our study was to examine the effects of gender on leucine and, for compari son purposes, lysine kinetics. Our subjects (n = 14) were seven matched pai rs of men and women selected for their exercise habits and age. After 1 wk of a standardized diet, they exercised at 50% of maximal O-2 uptake for 1 h . There was an effect of exercise in both genders: an increased leucine oxi dation and an attenuation in nonoxidative leucine disposal compared with re st (P < 0.05). Furthermore, our study confirms that there are gender differ ences in leucine, but not lysine, kinetics. Men had a higher rate of leucin e oxidation and a lower rate of nonoxidative leucine disposal during exerci se (P < 0.05). For women, a larger proportion of their exercise energy need s came from fat; for men, a greater fraction came from carbohydrate (P < 0. 05). We conclude that female exercisers rely to a greater extent on fat as an energy source, thereby using less carbohydrate, amino acid, and protein as a fuel source.