I’m Soy Confused… Is Soy Good or Bad For Me?

Easy Baked Tofu

Slice extra-firm tofu into thin slices and place on lined baking tray. Brush on this mix: 3 Tbsp. tamari + 1 Tbsp. oil + pinch of garlic powder + black pepper. Cook for 15 min. at 400º, then flip for another 10 min. Watch carefully so it turns golden but doesn’t burn. Use in wraps, stir fry, salads, or enjoy on its own.

I often get asked my views on the benefits/dangers of soy. Like chocolate or coffee, we’re hearing opposing verdicts: one week it’s creating better health, but the next… be careful or you’ll die! As someone who has eaten soy products on a near-daily basis for most of my life, I have personally seen only the benefits: I’ve maintained the same weight and size throughout my adult life, my cholesterol is low, and I’ve avoided diabetes, hypertension, and a whole host of other diseases. As a competitive athlete, I closely monitored my blood and it never once dipped out of the “optimal” protein range. And as a nerd, I’ve followed the science and have seen numerous clinical studies, health and cancer organizations, and medical professionals conclude: soy and its isoflavones have medical benefits and can actually help prevent cancer and other diseases. ** I am not a scientist, doctor, or dietician, so can only sum up some of the research I’ve come across. If you have questions or concerns about consuming soy, check in with your healthcare provider before making changes to your diet.

What is soy?

Soybeans are legumes native to eastern Asia that are high in iron, vitamin B, magnesium, zinc, potassium, and folate. Soybeans are especially known for their protein content, as they are a nutritionally complete plant protein—that is, they contain all 9 essential amino acids. Thus, soybeans are a viable replacement for meat, eggs, and dairy, packing in a lot of protein with zero saturated fat.

Soybeans are the basis for a number of products, but the highest quality forms (and also those that have been tested the most in clinical studies) are less processed and include: soybeans in their original form, tofu, tempeh, and soy milk. These are the foods you’ll want to prioritize over heavily-processed options, like textured vegetable protein (TVP), soy isolate found in protein shakes/bars, “meats,” and soy sauce.

What’s in it?

Soy contains isoflavones, which are plant-based compounds found to have estrogen-like properties. Years ago, this created some concern, due to the fear that soy might elevate estrogen in the body and contribute to hormone-associated cancers (e.g., breast, prostate). Early studies were conducted on rodents, who process estrogen much differently than humans. Rodent-subjects were also injected with much higher levels of isoflavones than would ever be consumed by humans. Thus, these results couldn’t quite be translated into human risk/experience. Initial studies that stoked the fire of fear also did not provide large or diverse samples of individuals, or account for other variables. In fact, one early Japanese study included a single subject: an 85 year-old woman who was given a “soy supplement.” The resulting data from that study is hardly reliable on a global scale!

 Cancer connection?

Within the past several years, numerous scientific studies have addressed the deficiencies in previous trials, and have provided much larger population samples, controlled variables, and more reliable data. A common thread throughout many of them: isoflavones in soybeans and whole soy products can actually diminish the risk of cancer onset or recurrence, as well as act in the prevention of other diseases. Isoflavones in soy are structurally similar to estrogen, but these phytoestrogens are not the same thing as female estrogens. Soy does not contain estrogen and whole foods don’t contain high enough levels of isoflavones to increase risk of cancers.

Thyroid connection?

There is also some ongoing debate about whether soy creates thyroid disease. Soy contains goitrogens, which can block iodine absorption and potentially affect thyroid function. One recent study did show that women with higher soy intake had a higher chance of seeing elevated levels of thyroid stimulating hormone (TSH), which might indicate an underactive thyroid. A similar result was not found in the male subjects, and the research is inconclusive. At this point, it has been found that iodine intake bears a much stronger correlation to thyroid problems than soy. But the research is ongoing. 

Connecting the dots:

Recent studies have repeatedly shown the benefits of consuming soy products across the board, and many health organizations and medical professionals tend to agree. This may be entirely due to the isoflavones in these products, or, more likely, it is a combination of things. People who are eating more soy proteins are likely eating fewer fried foods or animal products. That means: fewer hormones, saturated fats, and antibiotics that come associated with these products. Individuals consuming soy products are also more likely to eat a variety of fruits and vegetables, ingesting fewer processed foods and more vitamins and minerals, as well as more fiber.

The research consistently points to the fact that isoflavones in soy products are safe to consume on a regular (i.e., daily) basis and in moderate amounts (i.e., 1-2 servings/day). That said, individuals who are facing a cancer diagnosis or suspected hypothyroidism, as well as postmenopausal women (not included in the majority of the research), will want to discuss soy consumption with their doctor or treatment provider. It is also wise to choose an organic, non-GMO soy product, as most soy grown in the US is genetically modified and treated with dangerous pesticides.

Some recent studies:

Boutas I, Kontogeorgi A, Dimitrakakis C, Kalantaridou SN. Soy Isoflavones and Breast Cancer Risk: A Meta-analysis. In Vivo. 2022 Mar-Apr;36(2):556-562. doi: 10.21873/invivo.12737. PMID: 35241506; PMCID: PMC8931889.

Fan Y, Wang M, Li Z, Jiang H, Shi J, Shi X, Liu S, Zhao J, Kong L, Zhang W, Ma L. Intake of Soy, Soy Isoflavones and Soy Protein and Risk of Cancer Incidence and Mortality. Front Nutr. 2022 Mar 4;9:847421. doi: 10.3389/fnut.2022.847421.

Messina M, Mejia SB, Cassidy A, et al. Neither soyfoods nor isoflavones warrant classification as endocrine disruptors: a technical review of the observational and clinical data. Critical Rev Food Sci Nutr. 2021. doi:10.1080/10408398.2021.1895054.