There is a trend in research to identify foods that may impact cancer while a person has the disease. One area of research is the effect of dietary soy on breast cancer. Natural compounds in soy called isoflavones behave like estrogen. About two-thirds of women with breast cancer are known to have these estrogen-sensitive tumours and, in theory, these isoflavones could pose a risk to women with breast cancer. Animal studies show that these compounds may stimulate the growth of estrogen-sensitive breast tumours. As well, genistein, one type of isoflavone in soy, may reduce the effectiveness of Tamoxifen, a drug used in breast cancer treatment.
Some studies seem to show that soy is protective, while others demonstrate harmful effects. More research is needed, but the data suggest that isoflavone intake in amounts similar to that of a typical Asian diet likely does not result in harmful effects on breast tissue. This amount is equivalent to up to three servings per day of soy foods, such as tofu and soy milk. The American Cancer Society recommends that it may be wise to “avoid high doses of soy and soy isoflavones that are provided by more concentrated sources such as soy powders and isoflavone supplements.” Research on avoiding other foods or food isolates in relation to other cancers is limited.
If you’re in doubt, check with your doctor or dietitian. Likewise, if your appetite is very poor or you are very nauseated, be sure to mention it. There may be medication or strategies that can help.