What’s the deal with soy? Is soy bad for you? I often get asked these questions at my nutrition talks, and it’s not surprising given the number of claims on both sides of the issue that are being made by soy-related articles and books being published each year.
But what’s the truth about soy? Does it cause cancer? Is it bad for your thyroid? Can it disrupt your hormones? How do you separate fact from fiction?
Before jumping on the soy doom-and-gloom bandwagon, do your research. Become a food detective. Delve into the claims, and take a proper look at the scientific literature to see if the claims are actually based on sound science. You might be surprised at what you find.
Most of the arguments against soy are either based on unethical animal studies or isolated studies of people that have not been confirmed by other studies. Selectively choosing individual studies can allow you to prove just about anything. The real truth lies in looking at all the research and epidemiological studies collectively to draw conclusions based on the all the evidence.
So what does the collective data on soy and humans say? Well, it’s actually not as bad as you might think. But that doesn’t mean the evidence is conclusive and we can consume soy without caution. Let me explain.
There is a lot of speculation about how phyto-oestrogens in soy, called isoflavones, can disrupt our hormones and potentially cause breast cancer. It’s true that isoflavones bind with oestrogen receptors and can have effects similar to natural oestrogen. However, the effects are not nearly as strong as natural oestrogen—and research has shown either no association between soy and breast cancer or a protective association.
Many plant-based foods, including soy, contain goitrogens that can affect your thyroid function. Available research suggests that soy doesn’t affect your thyroid function if you have a normal thyroid. However, if you have an existing thyroid problem and take thyroid medication, you may need to exclude or reduce your intake of soy and other foods containing goitrogen. Talk to your doctor about it if you’re not sure.
Soy also contains antinutrients like phytates, which inhibit the absorption of minerals, and enzyme inhibitors, which interfere with digestion. The good news is that fermentation can release the nutrients and deactivate enzyme inhibitors. Fermentation also creates probiotics and vitamin B12. So opt for traditionally fermented soy products like tempeh, natto, miso, and soy sauce instead of unfermented soy products like tofu, soy milk, and edamame.
A word of warning—beware of “frankensoy”! Processed soy burgers, sausages, mock meats, cheeses, TVP, soy energy bars, and any other foods made from processed forms of soy. Processed soy is often treated with harsh chemicals like hexane, and nutrients get stripped away. Also, these processed soy products are likely to be loaded with added sugars, fats, refined flours, and preservatives.
- The Bottom Line on Soy and Breast Cancer Risk by Marji McCullough, ScD, RD
Health Benefits of Soy Foods: Separating Fact From Fiction: An Interview with Mark Messina, PhD by By Kirkham R. Hamilton, PA-C
- How Soy Can Kill You and Save Your Life by Dr Mark Hyman
Fiona Halar is a wholefood nutritionist and long-term vegan whose aim is to inspire people with engaging ideas, perceptive insights, and passionate action, to create vibrant health.
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