Highlights

Up to a third of breast cancer cases in Western countries could be avoided if women ate less and exercised more, researchers at a breast cancer conference said Thursday, renewing debate on a sensitive topic.

Obese women are up to 60 percent more likely to develop any cancer than normal-weight women, according to a 2006 study by British researchers. Many breast cancers are fueled by estrogen, a hormone produced in fat tissue. So experts suspect that the fatter a woman is, the more estrogen she's likely to produce, which could in turn spark breast cancer. Even in slim women, exercise can help reduce the cancer risk by converting more of the body's fat into muscle.

La Vecchia cited figures from the International Agency for Research on Cancer, which estimated that 25 to 30 percent of breast cancer cases could be avoided if women were thinner and exercised more.

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.

In one study from the Women's Health Initiative, as little as 1.25 to 2.5 hours per week of brisk walking reduced a woman's risk by 18%.

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