Is Soy a Risky Food?

By , Category : Food and Nutrition

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is soy riskySoy products are fairly common among Asian populations. They are introduced into their diets from a young age and regularly consumed throughout their lifespans. The average daily intake of soy per person is about 25 to 50 milligrams per day in Asian countries compared to only one to two milligrams per day in the U.S. Most studies that have demonstrated the health benefits of soy products have been conducted among Asian populations.

Their positive outcomes are likely a result of consuming minimally processed soy options, which are often fermented, such as boiled soybeans, tofu, miso, natto and soy milk.

Unfortunately, it is unknown if the health benefits can be similarly beneficial in an American population. Most soy products in the U.S. (i.e. soy flour, textured vegetable protein, and isolated soy protein in soybeans and soymilk) compared to most local food products are highly processed, which reduces the beneficial naturally occurring compounds.

Soy has received much controversy regarding its potential health detriments: Does it cause breast cancer or does it play a protective role? Will soy lead to increased risk of prostate cancer and decreased fertility among men? Can soy improve your cognitive health and prevent Alzheimer’s? Does soy interfere with thyroid functioning? All of these are questions that clients often ask me when I suggest they incorporate a vegetarian protein option into their healthy balanced diet.


Perhaps, I can help shed some light on some of these burning questions and put yourself at ease in incorporating soy foods into your diet!

Does Soy Increase or Decrease Breast Cancer Risk?

This is a very tricky question to answer since the research is ongoing and recommendations are constantly changing. Many epidemiological studies have demonstrated that there is no risk association between consuming soy products and developing breast cancer. Further, there also is no protective association.

In a study performed in 2008, researchers found that women consuming one serving of soy daily compared to women consuming none, had a 30% reduced risk of developing breast cancer. Furthermore, a review of 10,000 breast cancer survivors in both America and China have demonstrated a 25% reduced risk of recurrence among the group of women consuming more soy. However, there isn’t enough evidence to provide recommendations in which incorporating soy foods into your diet may either increase your risk of developing breast cancer or recurrence of breast cancer.

The benefits demonstrated in studies are generally seen among those who have introduced soy into their lives from an early age, which is usually only common among Asian populations. More so, many studies demonstrating beneficial effects, as mentioned, have been performed in Asian populations, whereas consumption is pretty low among American populations.

Soy Consumption During Breast Cancer Treatment

While soy and soy products should not be used as a treatment option to improve breast cancer outcomes, their consumption while undergoing treatment is inconclusive. There is not enough evidence to deem it safe to incorporate soy products into your diet while undergoing chemotherapy. Studies have shown that the phytoestrogen compounds found in soy products may inhibit or promote the growth of cancerous cells. Furthermore, they may mitigate the effects of some chemotherapy medications.

Therefore, it is advisable to just avoid intake to prevent any damaging effects. However, for the general public and for survivors, the American Cancer Society has recommended enjoying a modest intake of up to three servings of soy per day such as one cup of soy milk or half a cup of tofu. Just be cautious regarding incorporating soy protein isolates, which is a supplement found in natural health food stores. Their effects are not well understood.

Does Soy Consumption Reduce Infertility in Men and Increase Risk of Prostate Cancer?

The studies regarding the effects soy has on men’s health are limited. Many studies have concluded negative impacts regarding infertility based on case reports and animal studies. For instance animal studies have specified that soy may result in male breast development, decreased testosterone levels and increased risk of erectile dysfunction.

However, animal studies use mice and rats, which don’t even metabolize phytoestrogens the same way humans do. When rodents metabolize soy products, they produce far greater levels of isoflavones, a compound found in soy products, than humans do. So deriving similar conclusions doesn’t make sense.

One meta-analysis evaluating the effects soy has within a human population found that there was no effect on follicular stimulating hormone levels, which is a measure of fertility. More so, there was no effect on increasing testosterone levels, which is a risk factor for prostate cancer, nor was there an effect on reducing testosterone levels, which is a risk factor for infertility. Human studies have failed to draw any significant impacts soy may have on reducing infertility or increasing risk of prostate cancer among men.

Does Soy Consumption Negatively Impact Your Cognitive Health?

Several review studies have demonstrated that results among numerous trials in various ethnic populations are inconclusive regarding the impact that soy has on cognitive functioning. Therefore, the evidence is insufficient in stating that soy consumption would decrease your cognitive health and increase your risk of Alzheimer’s disease. Therefore, there is no reason not to consider incorporating a modest amount of soy into your balanced diet.

Does Soy Intake Interfere With Regular Functioning of Your Thyroid?

People have questioned whether consuming soy may lead to reduced thyroid functioning. A thorough review and two randomized trials have demonstrated that isoflavones, the compound found in soy products that are thought to interfere with thyroid functioning, do not play a significant role in doing so. However, for those who already have hypothyroidism and are on medications need to be careful with their soy intake. Soy has been shown to reduce the absorption of these meds. Therefore, people with hypothyroidism should take their hormone replacement medications on an empty stomach and separate from soy intake or as directed.

As you can see, the evidence is not very strong against incorporating modest amounts of soy into your diet. In fact, soy has many beneficial characteristics including antioxidant and anti-inflammatory properties. Furthermore, it is a great vegetarian protein source that provides all the essential amino acids your body requires. It can be quite versatile as it comes in many forms. I encourage you to incorporate soy products into salads, soups, or smoothies.

Just limit your intake to no more than two to three servings per day.

Sources for Today’s Article:
Dietitians of Canada, “Soy and breast cancer: what dietitians need to know,” Practice-based Evidence in Nutrition [PEN] November 2012;, last accessed May 4, 2015. Access only by subscription.
Dietitians of Canada, “Functional foods/nutraceuticals- soy: background,” Practice-based Evidence in Nutrition [PEN] January 2014;, last accessed May 4, 2015. Access only by subscription.
Dietitians of Canada, “Functional foods/nutraceuticals- soy: key practice points,” Practice-based Evidence in Nutrition [PEN] January 2014;, last accessed May 4, 2015. Access only by subscription.
Getz, L., “Soyfoods and cancer,” Today’s Dietitian, 2013; 15(4):30
McCullough, M., “The bottom line on soy and breast cancer risk,” American Cancer Society web site, 2012;, last accessed May 3, 2015.
Physicians Committee for Responsible Medicine, “Soy and your health,” Physicians Committee for Responsible Medicine web site;, last accessed January 11, 2016.
Thalheimer, J.C., “The top 5 soy myths,” Today’s Dietitian, 2014; 16(4):52.

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Leah Shainhouse, R.D.

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Leah Shainhouse is a Registered Dietitian with the College of Dietitians of Ontario and a member of the Dietitians of Canada. She graduated with a Bachelor of Science, Honors, in Nutritional Sciences from the University of British Columbia and went on to complete her dietetic training and Master of Science degree in Human Nutrition at McGill University. Leah has a strong desire to help shape the lives of individuals through a healthy lifestyle. She enjoys working with people to help... Read Full Bio »