Are soy foods safe?

Soy is a miracle food. I have been recommending this humble bean to my patients for many years. Scientific research has shown eating soy protects against heart disease, cancer and osteoporosis while easing the symptoms of menopause. It is also an economical and complete source of protein that can safely replace animal protein in the diet. Yet, from time to time, I have been questioned by readers who are concerned about any potential dangers from soy.

Like every good thing, over the years, soy has been blamed for all kinds of ills. Most of these accusations are based on anecdotal reports or shoddy research. The bulk of the 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 and cancer, specifically breast cancer, has to do with compounds in soy called phytoestrogens, the most abundant being the isoflavone, genistein. As their name suggests, phytoestrogens have chemical structures similar to the hormone oestrogen. This enables them to fit into the body's oestrogen receptor sites, much as a key fits into a lock.

Far from causing breast cancer, this ability to bind to oestrogen receptors allows phytoestrogens to block the effects of the much stronger oestrogens that are either produced by the body or come from toxic chemicals like insecticides. This is one way by which soy is thought to protect women against breast cancer.

Recent research has shown there is more than one type of oestrogen receptor. Soy isoflavones exhibit a selective blocking that offers cancer protection.

The research on large 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 the medical journal, Cancer, Epidemiology, Biomarkers, and Prevention provides compelling evidence of the anti-cancer effects of soy foods. This study found that with an increase in 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 cancers 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 theoretical. Certain compounds in soybeans can affect thyroid tissue in test tube studies, but this does not appear to be the case in live human beings.

Population studies show no increased prevalence of thyroid disease in countries with a high intake of soy, and the clinical research has been inconclusive. That debate aside, most researchers agree that consuming soy at the level needed to get its health benefits (about 25 to 40 grams 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 constant, have your thyroid function monitored periodically and make sure that you have enough iodine in your diet. Also be aware that taking thyroid medication at the same time as soy foods or any foods may decrease the drug's absorption. Take it on an empty stomach.

SOY AND NUTRIENTS

In raw soybeans, like almost all raw beans, there are substances that can interfere with the body's digestion and absorption of other nutrients. The way around the problem is simple: don't eat raw soybeans and eat a variety of other healthy proteins as well.

You may email Dr Tony Vendryes at vendryes@mac.com, or listen to An Ounce of Prevention on POWER 106FM on Fridays at 8 p.m.

RECOMMENDATIONS

Have some soy in your daily diet. At least 15 to 25 gm per day of soy protein is needed for optimal benefit. Soy is now available in many, many forms: soymilk, 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 a delicious and nutritious drink that can conveniently replace a meal.

Select high quality soy products. 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. Soy is an integral part of the Cellular Nutrition Programme I use for optimal nutrition.

Bottom line: I strongly endorse soy.

BENEFITS OF SOY

Soy foods confer a long and amazing list of benefits. It protects the heart, promotes good circulation, improves cholesterol balance, protects against breast, prostate, lung and colon cancers, and helps prevent osteoporosis and menopausal disorders. Even the FDA now allows soy product manufacturers to place claims about heart benefits on their product labels.