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October 10, 2020 • Healthy Eating & Nutrition

The Truth About Soy

Soy products isolated on white

There is perhaps no other food that has received more spin than soy!  Here are the facts based on my understanding of the science:

Whole soy foods have an exemplary nutritional profile, i.e. they are very, very nutritious.

o       Provide high quality, (“complete”) inexpensive vegetable protein that is naturally low in saturated fat and cholesterol-free.

o       Rich in vitamins and minerals, including B vitamins like folate, vitamin E, calcium, magnesium, iron, potassium and selenium.

o       High in soluble fiber (the type of fiber that reduces cholesterol and stabilizes blood sugar).

o       Provide heart-healthy polyunsaturated fats to include the superstar omega-3 fats.

o       Provide a broad array of phytochemicals felt to have specific disease-fighting capabilities, i.e. isoflavones, saponins, phytosterols and protease inhibitors.

o       Please note that only whole soy foods – soy milk, tofu, tempeh, soy nuts, miso and edamame, provide this wonderful bounty of nutrients, not isolated soy components or soy supplements.

The most well-documented health benefit of soy foods is reducing cardiovascular risk.  There is solid, demonstrable evidence that whole soy foods can lower total and LDL (bad) cholesterol levels.  The specific cholesterol-lowering effects of soy foods are due to its protein fraction.  To obtain maximal heart benefits, one should strive to consume 2 separate servings of soy foods daily.  For example – soymilk in your breakfast cereal or smoothie and a handful of soy nuts as a mid-afternoon snack.

It’s particularly beneficial to work towards substituting soy foods, i.e. soy burger for red meat that is high in saturated fats and often contain hormonal residues along with other harmful chemicals.  This way, you get the nutritional benefits of soy while simultaneously displacing unhealthy fat calories from your diet.

 Japanese miso soup in a brown bowl horizontal top view

Summary of potential benefits of whole soy foods:

1.      Everyone (men, women, children) can benefit from its healthy package of nutrients. FACT.

2.      Men and women (esp. women as they are at greater risk of osteoporosis) may benefit from the package of bone-protective nutrients and phytochemicals it provides.  LIKELY.

3.      Older women may experience a reduction in menopausal symptoms.  POSSIBLE.

4.      Men may receive protection from prostate cancer.  POSSIBLE.

5.      Everyone can benefit from its cholesterol-lowering properties.  FACT.

6.      Lactose-intolerant individuals (African Americans, Asians, etc.) can use soy milk as a lactose-free alternative to cow’s milk.  FACT.

7.      Women may receive protection from breast cancer.  POSSIBLE.

In regards to children – serving children whole soy foods as part of a balanced diet is safe, nutritious and consistent with health promotion.  I regularly serve my 4 children soy milk, soy nuts, tempeh and edamame (please see below for controversy on soy formula for infants).

This is the area where some controversy exists with soy foods.  The most noted is the effect of soy foods on patients with diagnosed breast cancer and whether the soy isoflavones stimulate or reduce tumor growth.  Although promotion of tumor growth is a theoretical concern, I suggest women with breast cancer discuss the potential risks/benefits with their health care provider to make an informed, personal decision. 

In regard to thyroid function – some animal studies show a link between soy isoflavones and possible thyroid disorders.  This appears to be highly controversial.  One of the arguments against this possibility is the observation that Asian populations that consume lots of soy foods do not have a higher incidence of thyroid disease.  I am comfortable with my thyroid patients consuming soy foods unless they have personally observed exacerbation in their condition as a result.

Recent concerns have emerged with soy infant formulas and the high concentration of isoflavones infants receive when virtually all of their nourishment is provided by soy (I consider this topic outside of the context of your article, but provide it to be complete.  Further studies are needed here).

The healthiest soy products are clearly the “whole” soy foods (soymilk, tofu, tempeh, soy nuts, edamame, miso).  They all have a similar nutritional profile and are very nutritious. 

Other reported benefits of soy foods include:

Cancer Protection– especially for the hormonally sensitive tissues of the breast, prostate and uterus.  Soy foods are the richest, dietary source of phytochemicals called isoflavones.  Isoflavones function in the body as weak estrogens and are thought to block the actions of the more potent biologic estrogens that can promote tumor growth.  Most of the evidence for soy’s cancer-protective properties are from population studies.  For example, Asian populations whose traditional diets are high in soy have much less of these cancers relative to Western populations who consume less soy.  Unfortunately, when you examine all of the available science – results are mixed.  Some studies show protection while others don’t.  We simply need more studies to know the definitive answer.  My “personal hunch” is that regular consumption of whole soy foods over one’s lifetime does reduce cancer risk.

A review of 18 epidemiologic studies looking at soy consumption and breast cancer reported a small (14%) reduction in breast cancer risk among women who had a high soy intake (April 5, 2006, Journal of the National Cancer Institute).

Reduction in Menopausal Symptoms – Soy isoflavones, again, through their estrogen properties, may provide relief of menopausal symptoms in women.  Like the studies with soy and cancer, results here are also mixed.  Based on my reviews of the science – some women benefit while others don’t.

Protection from Osteoporosis – The isoflavones, calcium, magnesium and “bone-friendly” vegetable protein found in soy foods appear to promote bone heatlh.  A large study from China recently published in the Archives of Internal Medicine (Sept. 12, 2005) found a significant reduction in fracture risk in women with high soy consumption.

Further studies are needed for conclusive proof of this reported benefit.

I recommend that people try them all – and regularly include those that suit their palate best.  In my experience, most everyone (including kids!) find edamame and roasted soy nuts delicious.  Tempeh and tofu are bland and tasteless on their own, but conveniently adopt the flavor of whatever you add to them, i.e. tofu in barbecue sauce.

My personal favorite is tempeh – a fermented soy product that has a firm, cheese-like texture.  I flavor it with a little olive oil, balsamic vinegar, salt and pepper and add it to salads or wraps.  My kids know it as “Asian cheese” and love it too!

I’m also a proponent of substituting organic, calcium fortified soy milk (Silk Enhanced is my favorite) for cow’s milk because of its nutritional profile is healthier.  Most adults’ taste buds can easily accommodate this transition in their morning cereal.

Whatever whole soy food one may choose – I always recommend organic, non GMO varieties.  A basic tenet of my personal nutritional philosophy is focusing on whole vs. processed foods.  As such, I am not as enthusiastic about processed soy foods (soy cheese, ice cream, meat analogs, etc.)  If someone insists on processed foods, however, soy products are generally healthier than their non-soy alternatives.