PURPOSE: Fluctuations in endogenous sex hormones over the menstrual cycle appear to influence dietary intake amongst inactive populations. Daily energy intake may be greater in the luteal phase compared with the follicular phase. The ad-libitum dietary intake following exercise across the menstrual cycle is unclear. This pilot study aimed to provide data on: 1) phase-related dietary intake in the post-exercise period; and 2) retention rates to aid future research.

METHODS: Female participants who exercised for >2.5 hours of exercise per week completed two familiarisation trials. In cycle 1 they monitored menstruation and during cycle 2 was a familiarisation of the dietary and exercise protocols alongside ovulation testing. In Cycles 3 and 4 they completed three-day weighed image-assisted diet records and training diaries in the early-follicular phase (days 2-4 of the menstrual cycle) and mid-luteal phase (7-9 days after a positive urinary ovulation test). On one day during each phase (four in total) participants undertook a fasted 60-minute cycling distance trial where sweat losses were assessed, followed by an ad-libitum meal. Hunger was assessed before, and immediately after exercise, and after the meal. 

Mean differences between the early-follicular and mid-luteal phases as well as between cycles 3 and 4 were calculated. Data are reported as n(%) unless otherwise stated. 

Correlations were determined using Pearsons correlation coefficient.

RESULTS: A total of 26 individuals expressed interest, 19 completed the screening questionnaire, of which 16 were eligible. Three participants were excluded before the completion of cycle 2 and five before the completion of cycle 3 due to menstrual irregularities. Eight participants completed data collection for cycle 4. The Mean differences between the mid-luteal and early-follicular phases were 456 kcal and 141 kcal for cycles 3 and 4 respectively. Although two (25%) participants had a lower energy intake in the mid-luteal phase during cycles 3 and 4, these were not the same in both cycles. 

There was no evidence of an association between hunger and energy intake at either the mid-luteal or early-follicular phase. 

CONCLUSIONS: The rate of menstrual irregularities was very high, causing 43.8% (n=7) of participants to be excluded. Post-exercise ad-libitum dietary intake appears to be greater in the mid-luteal phase which does not appear to be the case for hunger.  

The patterns shown in this pilot study are worthy of further exploration, and future interventional and observational studies investigating the nutritional intakes of female athletes may need to consider the effects of the menstrual cycle.