SUBSTRATE OXIDATION AT REST AND DURING EXERCISE - EFFECTS OF MENSTRUAL-CYCLE PHASE AND DIET COMPOSITION

The estrogen hormones have been shown to be highly glycogenic as well as lipolytic in nature. It is unknown whether the metabolic actions of estrogens impact upon energy metabolism during exercise. The composit ion of prior diet, however, does affect exercise energy metabolism. Th is study examined the influence of menstrual cycle phase (mid-follicul ar [FP; low estrogen] vs. mid-luteal [LP; high estrogen]) and diet com position on the rate of substrate oxidation for carbohydrate (CHO) and lipid at rest and during various intensities of physical exercise. Ni ne subjects completed an experimental session under four different men strual cycle-diet conditions: 1) FP following a 3-day high CHO diet [7 5% total caloric intake], 2) FP following a 3-day low CHO diet [35% to tal caloric intake], 3) LP following a 3-day high CHO diet, and 4) LP following a 3-day low CHO diet. In each of the experimental sessions s ubstrate oxidation was determined at rest and during cycle ergometer e xercise at intensities of 30, 50, and 70% VO2max, respectively. Statis tically significant (p < 0.05) interaction effects on substrate oxidat ion due to the menstrual cycle phase and diet conditions were found at rest and during 30% - 50% exercise. In general, CHO oxidation was low est and lipid oxidation highest in the LP under a low CHO diet conditi on.