Dietary fat may not raise breast cancer odds

By Amy Norton

NEW YORK (Reuters Health) - Contrary to some earlier research, a large U.S. study finds no evidence that a high-fat diet raises older women's risk of breast cancer.

In a study that followed more than 80,000 women for 20 years, Harvard University researchers found that fat intake during middle age or later was largely unrelated to breast cancer risk after menopause.

Nor was there evidence that any specific type of fat, such as saturated fat from animal products, altered a woman's odds of developing the disease.

Instead, there was some evidence that higher fat intake cuts the risk of breast cancer among women with insulin resistance, a precursor to diabetes.

It's possible, according to the researchers, that this potential benefit stems from lower blood sugar levels. In women with insulin resistance, a low-fat/high-carbohydrate diet can cause a particularly high surge in levels of insulin, a hormone that processes blood sugar. And some research suggests that chronically elevated insulin levels can feed breast tumor growth.

The study findings, published in the American Journal of Epidemiology, are at odds with some earlier studies that have linked high fat intake to a higher breast cancer risk.

However, other studies, like the current one, have failed to find a relationship between overall fat intake and breast cancer. Some research has suggested that certain healthy fats -- like the omega-3 fatty acids found in fish -- might lower a woman's risk of the disease.

"The take-home message for postmenopausal women is that limiting dietary fat is unlikely to reduce their risk for breast cancer," lead study author Dr. Esther H. J. Kim told Reuters Health.

It's unclear whether the findings pertain to younger women as well. Kim pointed out that some past studies have found a link between animal fat intake and higher breast cancer risk before menopause.

She and her colleagues based their findings on data from the Nurses' Health Study, which has followed thousands of U.S. women since 1976. The 80,375 women included in this analysis completed dietary questionnaires in 1980 and every two years thereafter; their breast cancer incidence was tracked through 2000.

When the researchers considered a range of other factors -- like age, weight changes over time, and family history of breast cancer -- they found that dietary fat had no significant effect on breast cancer risk.

"However," Kim said, "women should not feel this is a free pass to eat as much fat as they want."

For the sake of their hearts, she explained, women should limit saturated fats from meat and dairy products, as well as "trans" fats found in many commercial baked and fried foods.

In general, experts recommend a diet rich in fruits, vegetables, fiber and "good" unsaturated fats, like those in olive oil, nuts and fish. For women with insulin resistance, Kim noted, it's particularly important to have a moderate intake of good fats and to opt for fiber-rich foods over highly processed carbohydrates like white bread and sugary cereals.

SOURCE: American Journal of Epidemiology, November 15, 2006.