Phase-based eating is usually sold as a hormone lever. Eat these seeds in your follicular phase to raise estrogen. Eat these foods in your luteal phase to raise progesterone. It is a satisfying idea because it makes the body sound like a machine with labelled inputs.

The honest version is less tidy and considerably more useful, because the mechanism that actually connects food to your cycle is not about which foods. It is about whether there is enough.

The finding that matters most

In a controlled study of 29 regularly menstruating women, the pulses of luteinizing hormone that drive ovulation were disrupted once energy availability dropped below roughly 30 calories per kilogram of lean body mass per day.^[1]

Energy availability is the food left over after exercise has taken its share, measured against lean mass. Not calories eaten. Calories eaten minus calories trained away.

That single relationship explains more about food and the menstrual cycle than every phase-specific grocery list combined. The International Olympic Committee's 2023 consensus statement on Relative Energy Deficiency in Sport sets out where sustained low energy availability leads, including effects on bone, cardiovascular and metabolic health.^[3] Its clinical endpoint has an Endocrine Society guideline of its own.^[5]

So the first nutrition question in cycle-based wellness is not what to eat on day 9. It is whether you are eating enough to run a cycle at all.

What does change across the cycle

How much you want to eat

Energy intake measured within the same women's ovulatory cycles was significantly higher in the luteal phase than in the follicular phase.^[2] Resting energy expenditure also tends to run somewhat higher after ovulation.

This is the most practically important cycle nutrition fact for most women, because the standard response to it is to treat the second half of the month as a discipline failure. Restriction against a real physiological increase in appetite is the reliable way to produce the exact binge and guilt pattern the restriction was meant to prevent.

What you lose in blood

Menstruation costs iron. Heavy menstrual bleeding is a well documented contributor to anemia, fatigue and reduced quality of life in women of reproductive age.^[4] Iron intake is worth attention across the cycle rather than only during bleeding, since stores are rebuilt over weeks and not days.

Persistent fatigue that does not track your cycle is a reason for a blood test, not a reason to eat more spinach. Iron deficiency is common, it is diagnosable, and it is treatable.

What we actually recommend

28's nutrition guidance was built by certified functional nutritionists around nutrient-dense whole foods rather than restriction. In practice it reduces to five things, in order of how much they matter.

• Eat enough, especially if you train. This is the whole game. Training hard and eating less at the same time is the specific combination that breaks cycles.
• Let intake rise in the luteal phase. A modest, real increase in the second half of the cycle is normal. Plan for it so it arrives as food rather than as a 2am cupboard raid.
• Anchor meals in protein. It is the most satiating macronutrient and the most commonly under-eaten by women who are managing their weight, and it supports the training you are doing.
• Choose whole-food carbohydrates over cutting them. Carbohydrate restriction is a particularly poor fit for a body already at risk of low energy availability, and the luteal phase is when it fails hardest.
• Mind iron around bleeding. Especially if your periods are heavy, and especially if you are also training.

There are genuine phase-appropriate refinements on top of this, and we make them in the app. But they are refinements. If the base is not there, no amount of day-specific eating fixes it, and if the base is there, most women feel the difference before they get to the refinements.

The honest summary

Eating for your cycle works, and it works for a more boring reason than it is usually sold on. Not because certain foods speak to certain hormones, but because a menstrual cycle is an expensive process that the body runs only when conditions allow, and food is the main thing deciding whether conditions allow it.

This is general information rather than medical or dietary advice. Persistent cycle irregularity, suspected iron deficiency, or a history of disordered eating are all reasons to work with a clinician or registered dietitian directly.