Eating fewer calories for a month helps obese women lose weight and shrink their waist, but doesn’t yet reduce the deep belly fat or the fat under the skin — that takes longer, like with metformin.

For obese women with PCOS, taking metformin along with a low-calorie diet helps them lose more weight, shrink belly fat, lower male hormone levels, and get more regular periods than just dieting alone.

For obese women between 40 and 60 years old, losing visceral fat over 16 weeks through a reduced-calorie diet happens at the same rate whether or not they do resistance training. Adding resistance training does not lead to more visceral fat loss than dieting alone.

Even women without PCOS who are obese and take metformin with a diet lose weight and belly fat, and their SHBG (a hormone that binds male hormones) goes up — but their male hormone levels don’t drop like in women with PCOS.

For women who aren't very overweight, adding aerobic exercise to a calorie-restricted diet doesn't help them lose more fat than just eating less — as long as both groups burn the same total calories over 8 weeks.