Intermittent fasting for women: hormones, timing and how to start

Women can get many of the same benefits from intermittent fasting as men, including weight loss, better blood sugar control, less inflammation, lower blood pressure and lower triglycerides. The effects are often less dramatic, though, and the reason is hormones. Registered dietitian Julia Zumpano explains that fasting can affect the hormone that drives estrogen and progesterone. One theory is that fasting tells the body food is scarce, so it holds back ovulation. Lower hormone levels can bring missed or irregular periods, mood changes, hot flashes, headaches, poor sleep, low libido and even fertility problems.

Intermittent fasting isn't recommended if you're pregnant, breastfeeding or trying to conceive. After menopause, hormone levels stay low and steady, so fasting may work better, but caution still applies. To start gently, try a 12-hour overnight fast, such as 8 p.m. to 8 a.m. If that goes well for a week, add an hour at each end (7 p.m. to 9 a.m.), and work up to 16:8 over time. If you have periods, fast in the first days after your period starts and the week after. Ease off in the two weeks before your next period, especially in the final week, when your body is more sensitive to stress.

What you eat matters as much as when. Cut back on processed foods, choose lean protein, fruit, vegetables and whole grains, and break your fast with a meal high in protein and fibre, with some healthy fat, so your blood sugar doesn't spike. Eat slowly, and talk to a doctor or registered dietitian before you start.

General information, not medical advice. Don’t fast without talking to a doctor if you’re pregnant or breastfeeding, under 18, have had an eating disorder, have diabetes, or take insulin or other medicine that lowers blood sugar.