Last week, the US Food and Drug Administration (FDA) authorized the use on food labels of health claims about the association between soy protein and reduced risk of coronary heart disease. Although the authorization was specific to heart disease, some stories that appeared in the lay press may have been misleading. For example, a wire service story ran with a headline "FDA: Soy foods can be labeled as 'good for you'"; unless you read past the lead paragraphs, you might have thought soy received a blanket recommendation. In addition, at least two universities issued press releases about soy studies (in cells and in mice) which suggested some possible benefits of soy in cancer.
But while soy's effectiveness in heart disease has been substantiated, "in cancer, it is still a question mark," says registered dietitian Katrina Claghorn, a nutrition specialist at the University of Pennsylvania's Cancer Center. "Most assumptions about the benefits of soy in cancer are from epidemiological (population) studies, and more recently, from some animal studies. But it hasn't really gone beyond that. And some animal studies show that soy could actually promote certain cancers. So we're still trying to formulate what it is in the soy that may be protective, and what may be potentially harmful, and how it applies, remembering that all cancers are not the same."
There are components in soy which appear to offer some protection against colon cancer, Ms. Claghorn notes. But if you have estrogen-positive breast cancer, "there's a feeling that you probably should not have large quantities of soy because we don't know the impact of the phytoestrogens they contain. It's possible they could have the same cancer-promoting effects as estrogen."
If you are taking tamoxifen for breast cancer, or if you have a family history of breast cancer, you should also be cautious about the amount of soy you ingest, she cautions.
Therefore, the bottom line for soy in cancer is not the same as for heart disease. The recommendation is about 35 milligrams (mg) of soy isoflavones daily, and "up to 50 milligrams at most," she says. What does this mean in real terms? A half cup of tofu or tampeh has 35 mg of isoflavones, whereas a cup of soy milk has 20 mg.
"Don't go overboard, and eat the food in its whole form, rather than taking protein powders. When soy is in a food, it's also with other compounds, including vitamins and minerals, that contribute to the benefit," she advises. And when possible, choose lowfat varieties. "Some people think all soy products are low in fat, but that's definitely not true. A half cup of lowfat tofu has about 1.5-2.5 grams of fat, whereas the same size serving of regular tofu has between 5.5-6.5 grams of fat. It's the same with soy milk--one cup of lowfat has 2 grams of fat; regular soy milk has 4 grams."
For more information on soy, visit the US Soyfoods Directory of the Indiana Development Council, Talk Soy, the website of the United Soybean Board, and the USDA isoflavone database, which gives isoflavone values for 128 soyfoods and ingredients.