60–70% of women gain weight during perimenopause — not from eating more, but because five hormonal systems governing metabolism, fat storage, appetite and calorie burning shift simultaneously. Estrogen redirects fat to the abdomen. Progesterone loss removes 600 calories a month you were burning without knowing it. Insulin resistance increases. Leptin stops working. And FSH — a hormone nobody talks about — independently drives fat gain before estrogen even drops. Here's what's