Every month, your hormones move through a pattern. Not a straight line — a cycle. Estrogen and progesterone rise and fall in a sequence that has been repeating in your body since puberty, shaping your energy, your appetite, your sleep, your mood, long before you had language for any of it.
Most of us were taught to think of this as one event: the period. In reality, a menstrual cycle is four distinct hormonal phases, each with its own physiology. Understanding them will not fix a symptom. But it does give you a framework for noticing what your body has probably been telling you all along.
01. The Follicular Phase
The follicular phase begins on day one of your period and typically runs through day fourteen of a 28-day cycle, though the length varies from person to person. It starts low: estrogen and progesterone are both at their lowest point, which is also what triggers menstrual bleeding.
From there, follicle-stimulating hormone (FSH) signals the ovaries to begin maturing a new egg. As a follicle develops, it produces estradiol, and estrogen climbs steadily across the following one to two weeks.
Physiologically, this is often described as a building phase. Rising estrogen is linked to improved insulin sensitivity and, in some research, to better strength-training adaptations — one review of exercise studies found that resistance training performed in the follicular phase was associated with greater strength and muscle gains compared with the luteal phase. Energy and mood often track upward here too, though the research on mood specifically is far less consistent than the hormonal data, and individual experience varies widely.
02. Ovulation
Ovulation is brief but hormonally dramatic. When estrogen reaches a critical threshold, it flips from suppressing the pituitary gland to stimulating it, triggering a surge in luteinizing hormone (LH) that spikes roughly tenfold. That surge causes the follicle to release its egg, usually 36 to 44 hours later.
This is the shortest phase of the cycle and, for many, the one with the most subjective energy and confidence. It's also the point where a small rise in body temperature begins, driven by the hormonal handoff that follows.
03. The Luteal Phase
After ovulation, the ruptured follicle becomes the corpus luteum, which produces progesterone. This is the phase where progesterone dominates, and it changes how the body runs.
Progesterone has a thermogenic effect, raising resting body temperature by roughly half a degree — the same shift used in basal body temperature tracking to confirm ovulation has occurred. That temperature change affects sleep architecture, which is part of why sleep can feel lighter or more disrupted in the days before a period, even without an obvious cause.
Appetite tends to shift here as well. A systematic review and meta-analysis of 15 studies found that energy intake was, on average, about 168 calories per day higher during the luteal phase than the follicular phase. The leading explanation isn't a lack of willpower — it's that the body is metabolically preparing for a possible pregnancy and is less inclined to run a deficit. The researchers were clear that study quality varied and more rigorous work is needed, but the direction of the finding is consistent with what a lot of people already notice.
Physical performance research points the same direction: strength and aerobic output are, on average, somewhat lower in the luteal phase, particularly as estrogen drops and progesterone rises toward the end. The effect size in the literature is modest and inconsistent between individuals, so this is a pattern to be aware of, not a rule to plan your life around.
Toward the very end of the luteal phase, if pregnancy hasn't occurred, progesterone and estrogen both fall sharply. That drop is the direct trigger for the endometrium shedding — which brings the cycle back to day one.
04. Menstruation
Menstruation is technically the start of the follicular phase, but it deserves its own mention because it's where most of us start paying attention. Normal menstrual bleeding lasts eight days or less. Hormones are at their lowest point here, which is also, physiologically, a kind of reset before the climb begins again.
None of the Phases Is the Problem
It's worth saying plainly: none of these four phases is the "good" one. Lower energy in the luteal phase isn't a malfunction, and a lighter, more inward ovulatory-to-luteal shift isn't something to override. The research above describes averages across groups of people, not a verdict on any individual month.
That said, there's a real difference between a hormonal rhythm and a signal that something needs attention. Cycles that consistently fall outside the 21-to-35-day range, bleeding heavy enough to soak through protection hourly, pain that disrupts daily life, or cycles that stop altogether are not things to track your way out of. They deserve a conversation with a clinician, not a supplement or a spreadsheet.
Why This Matters Day to Day
You don't need a hormone panel to use this information. You need to notice: that a harder gym session might land better on day six than day twenty-four, that a bigger appetite the week before your period is physiology and not a lapse, that a lighter sleep pattern in the luteal phase has a name and a mechanism.
That's the whole premise behind how we think about nutrition at Alunae — matching what the body is asking for to the phase it's actually in, instead of applying one static approach to four very different hormonal states. The research is still evolving, and we try to say so honestly. But the pattern itself, the rise and fall repeating month after month, is not a theory. It's just biology, finally given some language.
Sources referenced: NCBI/StatPearls, "Physiology, Menstrual Cycle"; Oxford Academic, Nutrition Reviews systematic review and meta-analysis on menstrual cycle and energy intake; Frontiers in Endocrinology (2025), narrative review on exercise performance across the menstrual cycle.