Women who eat lots of soy foods appear to have a lower risk of breast cancer, but the benefits may come from health habits that go along with eating soy and not from supplements, researchers said on Tuesday.

Teams at Johns Hopkins University in Baltimore and Georgetown University in Washington looked at 18 different population-based studies of soy and breast cancer. They found an overall relative reduction of 14 percent in breast cancer risk in Caucasian women who ate soy, they reported in Tuesday’s issue of the Journal of the National Cancer Institute.

“We found that soy food intake was associated with a reduced breast cancer risk. However, we have no idea what soy supplements might do,” said Leena Hilakivi-Clarke of Georgetown.

Many of the studies involve people in Asia whose diets are naturally high in soy. In contrast, Western women often seek short cuts by taking soy supplements.

“At this point, women should not be taking high-dose soy supplements, especially those who are breast cancer survivors and women at increased risk for the disease,” said Bruce Trock, an associate professor of urology, epidemiology, oncology and environmental health sciences at Johns Hopkins.

“We need to take into account that Asian women are more physically active, drink less alcohol, have children earlier, and their entire diet is different from Western women - all of which decrease their breast cancer risk,” Trock added.

“The important aspect is eating actual soy-based foods like tofu, not highly purified isoflavone supplements. Highly refined components of soy can have very different biological effects than eating tofu or drinking soymilk.”

Soy is high in compounds called isoflavones, which may block estrogens, promote the destruction of faulty cells, including tumor cells, and fight inflammation.

Trock said the studies mostly relied on women to report how much soy they ate. As soy products are found in a wide range of processed foods, woman may have had no idea how much they were actually eating, he added.

And he noted there is evidence soy exposure early in life may be the most important factor in reducing cancer risk.

One of the studies showed Asian-American soy-eaters born in Asia had lower rates of breast cancer than those born in the United States, possibly reflecting soy exposure in-utero and before puberty. “But there are no studies that have followed women long enough to solidify this,” Trock said.