Is Soy Safe to Eat?

We’ve all heard it: soy is good for you! No wait, soy is bad for you! No, wait, it’s good for you, maybe! It’s confusing to figure out the final verdict. But in the world of nutrition rarely is there a final verdict. Research is constantly developing and changing what we know about nutrition and how it impacts the human body. However, in recent decades there have been over 10,000 peer-reviewed journal articles published about soy, or more specifically the isoflavones found in soy. So I read all 10,000 articles to write this blog for you all. Just kidding! I’ll briefly explore the most controversial topics surrounding soy, and as always I’ll post links to reliable sources for you to do more in depth reading if you’re interested.

If you’re vegan or vegetarian (VV), naturally you will come across soy and soy foods. Soy is a fantastic plant-based protein source and is a versatile legume. Let’s have a Forrest Gump and Bubba moment here...you can roast it, boil it, stir-fry it, steam it, there’s tempeh, tofu, soy nuts, soy milk, miso, soy protein isolate...you get my point. Like I mentioned, most of the research for soy is centered around isoflavones. These are plant estrogens, or phytoestrogens, that share a similar structure with the human form of estrogen. That means it can interact with the body’s estrogen receptors and have effects like estrogen or block the effects of estrogen. Let’s explore some of the main controversies that could affect your average adult vegan.

Feminizing Effects

Let’s go ahead and address this one first. If you’re a dude who eats soy, will you grow breasts? Only if you’re eating A LOT of soy. I’m talking 12-20 servings a DAY. And this evidence was from 2 case studies--or in other words only 2 men were studied and they experienced tender and swollen breast tissue, or gynecomastia. That should serve to quell fears and show how unlikely this is. Other concerns regarding negative effects on sperm and fertility have been shown through research to not be an issue. In fact research has shown that regular soy consumption in men has significant risk reduction for prostate cancer.

Cancer

There is a negative perception of soy and breast cancer, especially in regards to estrogen receptor positive breast cancer. However, research shows soy has either a neutral or protective effect against breast cancer. In fact, young girls who eat soy regularly have a lower lifetime risk of developing breast cancer. In general, the studies are using about 2 servings a day or less.

There is also evidence to support soy’s protective effects against colon and prostate cancer.

Thyroid

The research to date has shown soy products do not cause hypothyroidism in healthy adults. However, one 2011 study did show a faster progression to overt hypothyroidism in adults who already had subclinical hypothyroidism when consuming 16 mg of isoflavones from soy protein, an amount that would be typical of a vegetarian. Therefore for these individuals, it would be wise to avoid soy or greatly limit intake. For those who already have hypothyroidism and are taking thyroid medication, soy foods can affect absorption of the medication. It is advised to separate taking your medication by 1-3 hours before eating. Otherwise, it is safe for you to eat soy foods. Drastically changing the amount of soy foods you eat could affect the dosage needed for your medication. Check in with your doctor or pharmacist for questions regarding your thyroid medication and interactions.

Soy isoflavones can use up iodine that is needed to make thyroid hormone. Because of this, those who do not consume enough iodine can experience a negative impact on thyroid health from eating soy. For most Americans, about 50% of iodine consumption comes from dairy products. Therefore vegans in particular need to be aware of their iodine consumption to ensure adequate intake and prevent deficiency. Using iodized salt and eating foods such as seaweed contribute to iodine consumption.

Mineral absorption

Like other beans and whole grains, soy contains phytates and oxalates that can affect mineral absorption. The main concerns are around iron, calcium, and zinc. Iron was long believed to be poorly absorbed from soy, but thanks to new research techniques we now know that iron absorption is quite good from soy. Vegetarian women who eat 2-3 servings of soy daily have comparative iron status to women who consume meat. Calcium bioavailability in soy is also better than once thought. Absorption of calcium from soy milk fortified with calcium carbonate was nearly the same as from cow’s milk. Zinc absorption rate is about 25% less than from animal foods. However, soy is not a very good source of zinc to begin with.

GMO (genetically modified) Soy

GMO soy has been around for decades. As of yet there are no science-based links to adverse health effects, but many are concerned over potential health effects and ethical and environmental impacts. If it’s important to you to avoid it, buy products that are labeled USDA certified organic (organic foods cannot be genetically modified) or look for the non-gmo project label.

Bottom Line

Soy provides more protein than other legumes. For example ½ cup of edamame has about 11g protein while 1/2 c of black beans has about 7.5 g protein. The isoflavones found in soy have proven beneficial health effects. As long as you’re not allergic, there’s no need to avoid it completely. As with all foods, it’s best to stick with less processed versions: tempeh, soy nuts, edamame,etc. They retain the fiber, fatty acids, and isoflavones that make soy beneficial. Tofu  made with calcium sulfate and soy milk fortified with calcium and vitamin D make for a nutrient rich source of calcium in the vegan diet. Fermented forms of soy are great (miso, natto, tempeh), but not necessarily superior to non fermented. Highly processed soy or isolated soy protein products can be high in sodium, but it just depends on the product. As with other foods, look for short and simple ingredient lists. All things in moderation--for example, it’s ok to eat a processed soy burger if it helps you achieve your goal of avoiding a hamburger! It can be surmised from the research that 2-4 servings a day of soy would be beneficial. But keep in mind that there can be too much of a good thing and it would be prudent to keep this recommendation from Mark and Virginia Messina in mind: “Nevertheless, because an important dietetic principle is to consume all foods in moderation, and there is a wide variety of legumes from which to choose, a reasonable upper intake recommendation for soyfoods is four servings per day.”

What has your experience been with soy? We’d love to hear from you!

Sources:

Messina M, Messina V. The Role of Soy in Vegetarian Diets. Nutrients. 2010;2(8):855-888. doi:10.3390/nu2080855.

https://www.fertstert.org/article/S0015-0282(10)00368-7/fulltext

Safety of Soy Foods

https://vegetariannutrition.net/docs/Soy-Safety.pdf

Soy and Your Health

https://www.pcrm.org/health/health-topics/soy-and-your-health

Soy

https://veganhealth.org/soy/