The vast majority of medical, nutritional, and fitness research has historically been conducted on men, leading to health advice based entirely on the 24-hour circadian clock. While women certainly possess a circadian rhythm, those in their reproductive years also operate on a powerful second biological clock: the infradian rhythm, a distinct 28-day metabolic and hormonal cycle.
A woman’s metabolism, brain chemistry, and cortisol sensitivity shift drastically across the four distinct phases of her cycle (menstrual, follicular, ovulatory, and luteal). For example, during the follicular and ovulatory phases (the first half of the cycle), estrogen levels rise, making the body highly resilient to stress, exceptionally efficient at burning carbohydrates, and primed for high-intensity workouts and muscle building.
Conversely, during the luteal phase (the week leading up to menstruation), progesterone dominates. Progesterone elevates the resting metabolic rate—meaning the body naturally requires more baseline calories—but it also makes women significantly more sensitive to the stress hormone cortisol. Forcing intense caloric restriction or grueling, exhaustive workouts during this phase can inadvertently trigger fat storage, muscle breakdown, and severe premenstrual symptoms.
True wellness for women involves working with this biology rather than fighting it. By aligning nutrition, exercise intensity, and rest with these shifting hormonal tides, women can optimize their energy, stabilize their mood, and protect their long-term endocrine health.
