After studies several years ago linked hormone replacement therapy to cancer, millions of women abandoned the treatment, leading to a sharp drop in breast cancer rates. Experts said a similar reduction might be seen if women ate better — consuming less fat and more vegetables — and exercised more.
Holmes said changing one's diet and nutrition is arguably easier than tackling other breast cancer risk factors.
"Women who have early pregnancies are protected against breast cancer, but teenage pregnancy is a social disaster so it's not something we want to encourage," she said. "But there's no downside to reducing obesity and increasing physical activity."
In the 1980s and 1990s, breast cancer rates steadily increased, in parallel with the rise in obesity and the use of hormone replacement therapy, which involves estrogen.
The American Cancer Society recommends 45 to 60 minutes of physical activity five or more days a week to reduce a women's risk of breast cancer.