David L. Katz, MD, responds to a reader in the September 2007 issue of The Oprah Magazine about the merits of eating soy in relation to preventing cancer. His response causes me to pause even more about jumping on any diet bandwagon.

Katz says we should eat soy foods -- just not too much because the evidence linking soy to breast cancer, for example, is mixed.

In comparing soy-eating Japanese women with American women who eat very little soy, researchers find lower rates of breast cancer in the Japanese women. But in a test tube, soy's plant estrogens can speed cancer cell growth. Maybe soy behaves differently in the body than it does in a tube. Or maybe soy has both negative and positive effects on breast cancer. Perhaps it's not soy at all. It could be that the populations eating soy are benefiting from not eating something else, like meat -- the saturated fat found in red meat has been linked to higher cancer rates. Replacing steak with something else may be the protective key.