If you gain weight and then lose it, will your bra size also change?

It can: Breast tissue is composed of mainly fat, with some connective tissue for support and the glandular tissue for making milk. That fat, like all the rest of the fat cells in your body, can store the fat from foods you eat. Exercise and changing fat intake in your diet can make you burn fat, which comes from all areas including breasts (which is why you can't just lose your belly or thighs or hips)