Men Are the Sun, Women Are the Moon: Why Cyclical Biology Changes Everything

On why a lot of health advice isn't built for you — and what to do about it.

There's an image I keep coming back to: men are the sun, women are the moon. The sun runs on a consistent rhythm — it rises, it sets, roughly the same arc every day. The moon is cyclical. It waxes, it wanes, it disappears and comes back. Both are natural. Both are necessary. But they do not work the same way, and pretending they do is how we end up with health advice that only works half the time for half the population.

The research gap

Until 1993, women of "childbearing potential" were routinely excluded from most clinical drug trials in the United States. The FDA didn't require meaningful inclusion of women in pivotal studies until that year. That means for decades, the medications your mother was prescribed — and some you are still prescribed today — were tested primarily on male bodies.

Women don't run on a 24-hour rhythm. Or rather — we run on that plus a ~28-day one. The hormonal orchestra of a cycling woman is not a tidy daily loop. It's a monthly symphony with crescendos and rests.

What the moon metaphor actually means

The menstrual cycle is a rhythm. Perimenopause is what happens when that rhythm becomes less predictable — the moon still waxes and wanes, but the tides get more dramatic. Dr. Nanette Santoro, a reproductive endocrinologist who has published extensively on perimenopause physiology, describes this period as characterized by greater variability, not just a slow fade.

Treating your biology like a male system with a monthly inconvenience attached gets you things like:

• Advice to eat the same way every day, when your metabolism and appetite hormones shift across your cycle
• Supplements formulated for a steady hormonal state, when yours isn't
• Medications dosed without regard for where you are in your cycle
• A medical system that often treats perimenopause as "you're just stressed"

What changes when we honor the cycle

When we build products, protocols, and education for cyclical biology, we get better outcomes — not because women need special treatment, but because we've finally stopped pretending we're working with the same system. The Menopause Society (formerly NAMS) has been calling for more sex-specific and cycle-aware research for years, and the evidence base is finally catching up.

The takeaway

You are not a man with different plumbing. You are running a fundamentally different operating system, and in perimenopause, that system is going through its biggest update in decades. The sun is steady. The moon is powerful. Both deserve health care designed for how they actually work.

Educational content, not medical advice.