Experts are still trying to understand the connection between obesity and breast cancer risk, but it's clear that being significantly overweight, especially in the midsection, increases breast cancer risk in postmenopausal women.

Estrogen is stored in fat tissues, so after menopause, when the ovaries are no longer producing estrogen, having excess fat leads to higher estrogen levels. If your mother was thin as a younger woman but gained weight later in life, it's of more concern than if she was heavy all along.