In the FLO

In the FLO argues that women organise their lives around a 24-hour clock that was studied mostly in men, and that a second and longer rhythm — the roughly 28-day menstrual cycle, which Vitti calls the infradian rhythm — should be driving decisions about food, exercise, work and social commitments. Her claim is that fighting that rhythm produces the fatigue, symptoms and burnout many women accept as normal.

The framework divides the cycle into four phases — follicular, ovulatory, luteal and menstrual — and assigns each a pattern: heavier training and new projects when energy and estrogen are rising, more carbohydrate and more recovery in the luteal phase, and genuine rest around menstruation. She extends the same logic to skincare, work scheduling and relationships.

It is written for women with cyclical symptoms who want structure and a reason for what they are experiencing, and many readers describe the framing itself as the useful part. The system assumes a natural cycle, so it applies differently to women on hormonal contraception, and not at all after menopause.

On evidence, be precise about which layer you are evaluating. The underlying physiology is real: hormone concentrations shift across the cycle and influence body temperature, substrate use, fluid balance and mood in measurable ways. The specific claim built on top of it — that matching diet and training to cycle phase produces better body composition, performance or symptom outcomes — has very little controlled support. The trials that exist on phase-based training are few, small and inconsistent, and nothing of comparable rigour tests the full program. Vitti writes with more certainty than that evidence allows, and the popularity of cycle syncing has outpaced its testing by a wide margin. Read it as a structured hypothesis about your own cycle, worth tracking rather than assuming.