The menstrual cycle can have a real influence on a female athlete’s energy levels and energy intake. During the follicular phase, days 1–13, where day 1 is the first day of your period, oestrogen levels are rising and peak just before ovulation (days 14/15), while progesterone levels are low. During the luteal phase, days 16–28, oestrogen levels decrease, falling to the lowest level just before your period starts; progesterone is at its highest point midway through this luteal phase. These hormones control what type of fuel you oxidize/utilize.