Cancer Control

Ask a doctor about the best ways to prevent breast cancer, and you're likely to hear about a number of things you can't easily control: being blessed with the right genes, hitting puberty later than age 12, having your first child before you're 30. It's not exactly a basis for action. Increasingly, though, physicians are mentioning a few things you can do that just might help reduce the frightening 1-in-8 odds of getting breast cancer. They include keeping to a low-fat diet, watching your weight, avoiding stress and getting plenty of exercise.

The strongest evidence that lifestyle can make a difference comes from studies of women who have already had breast cancer. A study published in May found, for instance, that patients who had switched to a low-fat diet, with no more than 20% of their daily calories derived from fat, had a 24% lower rate of breast-cancer recurrence within five years than women who did not alter their eating habits. Another 2005 study found a similar benefit from exercise. Breast-cancer patients who walked briskly for one to three hours a week had a 25% lower death rate from the disease than sedentary patients. The finding has oncologists urging patients to get moving.

Exercise and a low-fat diet are good for you in principle, but whether they cut the risk of breast cancer for women who have never had the disease is still being investigated. "I don't think we have enough evidence yet," says Dr. Therese Bevers, medical director of cancer prevention at MD Anderson Cancer Center in Houston. Cutting back on fat does, however, make sense in theory. From 60% to 70% of primary breast cancers are hormone dependent--they grow in response to estrogen. Excess dietary fat primes the ovaries to release more estrogen, which in turn promotes tumor growth. And yet studies don't consistently show that low-fat diets lead to less cancer. That may be because other dietary elements, including overall calories, also influence tumor development by affecting growth factors and hormones like insulin, which also promote cancer.

Weight is another risk factor related to fat that may affect breast tissue through its own routes. Before menopause, women who are overweight may enjoy a slightly reduced risk of breast cancer, most likely because they ovulate less often than do thinner women, so their breasts are exposed to less estrogen. After menopause, however, heavier women are at greater risk. That's probably because once the ovaries stop churning out estrogen, the body's fat cells become its primary source of the hormone. Losing excess weight is one concrete step that women can take to reduce the risk of developing breast cancer after menopause.

Even women with genetic mutations that give them an 80% risk of getting the disease in their lifetime can benefit from such weight loss. A recent study found that overweight women with BRCA1 mutations who dropped more than 10 lbs. before their 30th birthday cut their risk of developing breast cancer 65% over the next two decades.