Previous research has shown women on normal mixed diets have varied blood lactate (LA) responses to exercise across their menstrual cycle (MC) phases. This study examined the effect of diet on this finding. Eurmenonrheic women (n=10) completed a discontinuous exercise protocol consisting of 4 intervals of 6 min exercise, separated by 6 min rest, at 30, 50, 70 and 90% V̇O2max. The exercise was performed after a 3 day pen od under each of the following conditions: 1 - low carbohydrate (35% of total caloric intake) - mid-follicular phase (LCHO-FP), 2 - low carbohydrate - mid-luteal phase (LCHO-LP), 3 - high carbohydrate (75%) - mid-follicular phase (HCHO-FP), 4 - high carbohydrate - mid-luteal phase (HCHO-LP). Eucaloric status was maintained during the study. The MC phase was confirmed by blood hormonal levels. Significant (P<0.05) MC phase - diet interaction effects were found. LA was lower at 70% V̇O2max in the LCHO-LP (3.7±0.2 mmol·l-1) than at the other conditions (5.0±0.7 to 6.0±0.7 mmol·l-1; mean ±SEM). Also, LA during LCHO-LP at rest and all other exercise intensities tended to be lower than all other MC phase/diet conditions (P<0.06). LA responses at rest and during exercise in the HCHO-LP, HCHO-FP, and LCHO-FP conditions did not differ significantly. The present findings demonstrate that an "athletic type diet", high in carbohydrates, negates the menstrual cycle phase difference in lactate responses to exercise previously reported in the literature; however, the menstrual phase differences do exist when a diet low in carbohydrates is consumed.
Keywords: Diet; Exercise; Lactate; Menstrual cycle.