From time to time, we hear that soy foods are unsafe. What is your take on this?
Soy foods are varied and range from the whole, cooked bean to highly processed and refined products. Soy has been popularized, especially by Adventists, who find it a suitable source of protein. Amino acids, the building blocks of protein, occur in most of our foods, and the only problem a vegetarian is likely to experience with protein is if one’s diet is not varied and balanced.
Vegetable sources of protein often lack an essential amino acid or two, and soy beans are one product that provides a more rounded amino acid profile. The use of animal products provides a good range of amino acids within the single food, but such an advantage does not hold when compared to a mixture of foods. For the vegetarian, mixing grains with legumes and nuts provides a full spectrum of amino acids that is totally satisfying to all kinds of people—athlete, growing adolescent, or even the pregnant mother-to-be. This means that soy products, as good as they are, do not have to be a part of the vegetarian diet for it to be satisfactory.
In all probability, however, there is an advantage to soy that transcends amino acid content. While there is evidence for several advantages to soy, this evidence is not of the most compelling order, because studies on food effects are very difficult to perform. Nevertheless, it’s probable that soy offers protective isoflavones and other such phytochemicals to decrease one’s risk of cancer. For men, this appears to be the case for prostate cancer, with a glass of soy milk a day providing a modicum of protection.
The anti-soy lobby brings all kinds of arguments to support their condemnation of soy. Some cite situations in which birds fed an essentially total soy diet developed crooked beaks. Others quote studies that suggest an increase in dementia for those consuming large quantities of soy. The important thing is to recognize that these are inconclusive studies and are being given disproportionate weight by those quoting them.
A few months ago there was a very well-conducted study of sufficient numbers and controls reported in The Journal of the American Medical Association(JAMA, December 9, 2009, vol. 302, no. 22) on soy food intake and breast cancer survival. This study, conducted on women in China, was able to separate soy intake into four quartiles and correlate it with survival from breast cancer. There were more than 5,000 female breast cancer survivors, followed for some five years. Those in the highest quartile of soy intake had some 30 to 40 percent less cancer recurrence. This advantage was experienced regardless of tumor estrogen receptor status, but did not increase where the intake exceeded 11 grams per day of soy protein.
This suggests a benefit to soy up to a limit. One of the difficulties in transferring this advantage to the United States might be that the Chinese tend to consume “whole” soy, not the texturized protein many in the U.S. utilize. Certainly, whole soy products such as soy milk, tofu, the whole bean, or miso (a traditional Japanese seasoning) appear to confer an advantage to female breast cancer survivors. Because this study is of high quality, it has significant meaning for breast cancer survivors and is encouraging to those who utilize soy—particularly whole soy—as part of their diet.
While benefit in this one situation does not necessarily apply across the whole spectrum of potential advantages or disadvantages, it is supportive of our recommendations that moderate amounts of soy be utilized in a balanced vegetarian diet.