Still unsure about soy? This week's newsletter is part 1 of a two-part series that takes a closer look at the risks and benefits associated with this controversial compound.

I have received many questions about soy, prompted by my previous newsletter, entitled "The Soy Renaissance" (October 20, 2011). There is a great deal of misunderstanding, as well as differences of opinion, on the health benefits of soy foods, which is why I'd like to expand on this controversial topic over the next two weeks.

Throughout my writings, I repeatedly applaud the versatile and potent health benefits of the soybean. In recent times, however, there has been considerable controversy surrounding these benefits. Predictably, the most vocal criticisms of soy have come from the meat and dairy lobby and their representatives in the media and scientific community.

Soy is probably the prime example of a "medicalized" food. Its health benefits are demonstrable and documented, and I stand behind my recommendations to include soy as part of a balanced diet, in food or dietary supplement form. Soy contains several nutrients and phytochemical fractions that may be beneficial for health.

Too Good to Be True

On the downside, unprocessed soybean is unfriendly food. It doesn't appeal generally to the Western palate. The flatogenic (intestinal-gas-forming) potential and strong aftertaste of unprocessed soy are drawbacks. However, modern food processing and ancestral fermentation techniques render soy foods palatable. These processes alter the flavor and texture of soy foods so that they appeal to many taste preferences.

Most soy foods consumed in Western society are highly processed, and as a consequence, they may be lacking in the healthful compounds that give soy its benefits. The former widespread inclusion of hydrogenated soybean oil in "junk foods" may have left its mark on cardiovascular health. We need few reminders concerning the demonstrated negative health consequences of hydrogenated oils, especially if they contain significant amounts of trans-fatty acids.

The Health Benefits of Soy

After much lobbying, the Food and Drug Administration provided their support for the claim that soy protein in the correct amount (25 grams/day) and form is capable of lowering blood cholesterol and preventing heart disease. While this cardiovascular health benefit for soy is real, it must be consumed consistently (in the same amount and form) in order to achieve this desired health benefit.

Evidence that soy protein in a dose of at least 25 grams per day can be expected to lower blood cholesterol is quite convincing. In fact, this health advantage of soy has been known for approximately 50 years and has been confirmed in meta-analysis studies. One impediment to the popularization of soy protein for cholesterol lowering in medical practice has been an incomplete understanding about how soy lowers blood cholesterol.

The amino acid profile of soy protein is known to affect insulin/glucagon ratios in the blood and induce changes in the liver that may affect cholesterol synthesis and transport. Soy seems to alter thyroid status by producing modest elevations of serum thyroxine levels in animals and humans and it has been associated with thyroid insufficiency. Whole soy food contains soluble and insoluble soy fibers that can assist in cholesterol lowering by interfering with fat and cholesterol absorption.

Fermented or Non-Fermented Soy?

Some nutritionists emphasize that the health benefits of soy are most likely to be delivered when soy is consumed in a fermented format. I tend to agree, based on population studies. Soy has been a dietary staple in Eastern Asia for thousands of years, and traditional, soy-based diets are composed often of fermented soybean products including miso, natto or ancestrally fermented tofu.

Epidemiological studies show that the occurrence of breast or prostate cancer, heart disease and adverse symptoms associated with the menopause are less in populations consuming soy. While I reiterate that the type of soy consumed in these populations is of the fermented variety, modern research with processed fractions of soy demonstrates health benefits.

The real advantage of soy fermentation is the partial digestion of protein and carbohydrate components of this legume. Enzyme inhibitors (so called "anti-nutrients") within soy are often denatured, removed or neutralized by fermentation and unabsorbable carbohydrate fractions of soy that cause digestive upset are eliminated to a major degree.

Isoflavones: Good or Bad?

Recent research on the absorption of soy isoflavones shows that these compounds have a greater bioavailability (enhanced absorption) when consumed in deconjugated form. The conjugated isoflavones genistin, daidzin and glycetin are converted to their unconjugated forms (genistein, daidzein and glycetein) by the breaking of a chemical bond during fermentation.

Therefore, fermented soy can be expected to present highly absorbable isoflavones that can be efficiently utilized by the body. There are also advantages to soy supplements, which contain predictable amounts of certain helpful components of soy.

Next week, I will examine more controversies that surround the consumption of soy for health.

Be Healthy!
Dr. Stephen Holt, M.D.