Of all the things you can do to reduce risk, this tops the list; it’s even more effective than quitting smoking and drinking, studies show. “If you have a lot of fat cells, you have more circulating estrogen, and increased estrogen is associated with breast cancer risk,” explains Buchanan.

This especially holds true for older women. One 2012 study of 6,400 postmenopausal women found that those who are obese have 50 percent more circulating estrogen than those of healthy weight. And according to AICR, a woman with a body mass index, or BMI, of 30 (classified as obese) has a 13 percent increased breast cancer risk compared with a woman with a BMI of 25 (slightly overweight). So cut back your portions and get moving; exercise also reduces risk.