Out of all the foods out there, soy seems to generate a lot of controversy. Soy contains many nutrients and plant chemicals. Isoflavones are compounds found naturally in soy that can impact hormonal health. For example, soy isoflavones may help minimize some of the symptoms of menopause like hot flashes. Soy consumption has been associated with a number of benefits such as improved heart health and even reduced breast and prostate cancer risk.
That being said, soy has also been feared for a number of different reasons. One reason is that many believe soy can shut down thyroid function by reducing the production of thyroid hormones. Lab studies not conducted on humans have found that soy isoflavones can inhibit an enzyme called thyroid peroxidase (TPO). TPO helps to make inactive and active thyroid hormone (T4 and T3).
A large amount of studies have been conducted in recent years to examine this question. Studies show that in healthy people, soy consumption does not appear to increase the risk of developing hypothyroidism.
Where things become more unclear is in those who already have lower thyroid function. This may include those who have abnormal TSH levels even though other thyroid tests are normal. In cases like these, soy isoflavones in high enough quantities can raise TSH levels enough to have a negative impact on thyroid health. More research is needed to confirm this and work out the details such as what quantity of dietary soy could have this impact.
In general, soy is a healthy food when prepared in a healthy way. By “healthy way”, I mean minimally processed soy such as a homemade tofu Thai curry rather than a soy hot dog full of other additives. I don’t like to restrict generally healthy food from patients unless there is a good reason to. If a patient is wondering whether to reduce soy in their diet to help their thyroid, my answer will vary depending on the case.
If you’re wondering how evidence-based naturopathic medicine can support healthy thyroid function, feel free to book a free 15 minute consultation.