Dr Vendryes: TO SOY OR NOT TO SOY?
I consider soy a super food. I have been recommending this humble bean to my patients for many years. Scientific research has shown that eating soy protects against heart disease, cancer and osteoporosis, while helping hormone-related problems like menopause.
It also is an economical and complete source of protein that can safely replace animal protein in the diet. Yet, from time to time, readers have expressed concern about any potential dangers of soy.
Like many good things, soy has been blamed for all kinds of ills. To my mind, most of these accusations are based on anecdotal reports or shoddy research. The bulk of medical evidence confirms the valuable role of soy in preventing disease and supporting health. Let's look at the most common concerns.
Soy and cancer
Much of the worry about soy has to do with naturally occurring compounds called phytoestrogens, the most abundant being the isoflavone, genistein.
As their name suggests, phytoestrogens have chemical structures similar to that of the hormone oestrogen, but they are not oestrogen.
This similarity in chemical structure enables these isoflavones to fit into oestrogen receptor sites on various cells, much as a key fits into a lock. Thus, they exhibit an oestrogen-blocking or anti-oestrogen effect in the human body.
Far from causing breast cancer, this ability to bind to oestrogen receptors allows phytoestrogens to control the effects of the much stronger oestrogen that are either produced by the body or come from toxic chemicals like insecticides or industrial chemicals. This is one major mechanism by which soy is thought to protect against diseases like breast and prostate cancer, uterine fibroids, breast lumps and cysts.
The majority of research, as well as the experience of Asian populations where soy has been a dietary staple for thousands of years, confirms the protective role of soy. A report published in the May 2001 issue of Cancer, Epidemiology, Biomarkers, and Prevention provides compelling evidence of the anti-cancer effects of soy foods. The study found that, with an increase of soy intake during adolescence, there was a reduction in the risk of breast cancer. Women with the highest consumption of soy had only half the risk of those with the lowest intake. Other studies have also shown a reduced risk of cancer of the prostate and colon with increasing soy consumption.
Soy and the thyroid
Another charge against soy is that it contains 'anti-thyroid agents' that can disturb the function of the thyroid gland. This is largely a theoretical concern. A number of healthy foods like cabbage and soy contain substances called goitregens. These substances, in very large amounts, can affect thyroid tissue in test tube studies, but this does not appear to be the case in live human beings. In research on animals, once there is sufficient iodine in the diet, no such problem occurs.
Population studies show no increased prevalence of thyroid disease in countries with a high intake of soy, and the research on patients with thyroid problems has been incon-clusive. That debate aside, most researchers agree that consuming soy at the level needed to get its health benefits (about 25 to 50 grammes per day) is most unlikely to impair thyroid function. After using soy with hundreds of patients, I have detected no disturbance of thyroid function that I could blame on soy.
However, if you have an underactive thyroid, a bit of caution may be in order. Try to keep your soy intake fairly consistent, take an iodine supplement and have your thyroid function monitored periodically. Also, be aware that taking thyroid medication at the same time as foods (soy or otherwise) may decrease the absorption and effectiveness of drug. Take thyroid medicines on an empty stomach.
Include some soy products in your daily diet. Soy is now available in many, many forms - soymilk, soy based shakes, soy cheese, soy nuts, soups, drinks, protein bars, tofu and tempeh. There are also textured vegetable protein products like veggie mince and soy burgers. My favourite way to have high-quality soy each day is with a soy-protein shake. This is actually a very nutritionally balanced meal in a convenient drink. It provides all the basic nutrients (including some iodine) for optimal nutrition, along with the additional benefits of soy
Enough healthy protein is a vital part of your diet. Select high-quality soy products as not all soy foods are of equal value. Many so-called soy products have low levels of the substances that provide the health benefits of soy. Look for the term 'soy-protein isolate', and check the protein content on labels as a guide in assessing soy products.
It also makes good nutritional sense to consume other forms of healthy protein like peas, beans, fish, organic eggs and organic poultry. Let your food be your medicine.
- You may email Dr Vendryes at email@example.com or listen to An Ounce of Prevention on POWER106FM on Fridays at 8:15 p.m. Details of his books and articles are available at www.tonyvendryes.com.