Does Soy Consumption Affect Thyroid Health?

Last Updated on

There has been a lot of controversy over much a small legume as soy.

Is there any reason to be really worried about soy? Or do people only tend to believe rumors and write off the use of soy without any clear scientific evidence?

For many years now, people, especially hypothyroidism patients have been avoiding the use of soy.

But is there really a reason to do so?

What will follow, is an extensive discussion on the various effects, both positive and negative, of soy on our health, and especially the thyroid function and hypothyroidism patients.

What do you need to know about soy?

Soy is quite a controversial food product, often used by vegans and vegetarians to satisfy their daily requirements for protein. Soy is used to produce products such as tofu, tempeh, soy milk and much more, also often used by vegans and vegetarians.

Soybeans are a type of legume which is very commonly processed in order for a variety of soy forms to be produced. Soybeans can also be consumed as a whole.

A soy protein extract is to be found as well, and added to any meal, or smoothie, for the purposes of ingesting introducing it as a part of the diet. The reason why soy is one of the beloved food products, especially by vegans and vegetarians, is because of its good nutritional value.

Around 28g of soy isolate powder[i] offers us with the amazing 23g of clean protein, only 1g of carbs and 2g of fats, and of course, copper, manganese, iron, fiber, etc.

The soy protein is a clean protein, which is rare when it comes to plant-proteins.

Soy helps build good and strong muscle mass[ii], it promotes weight loss[iii], and it even helps lower the “bad” cholesterol while raising the “good” cholesterol[iv].

However, as we mentioned earlier, soy is rather a controversial food product, despite the many scientific studies that have proven the positive sides of soy. There are divided opinions on the use of soy, especially regarding its effects on our thyroid health, thinking about how it can possibly affect the ones that are struggling with hypothyroidism.

So, let’s look into the possible positive and negative effects of soy on our thyroid health.

The potential negative effects of soy on our thyroid health

For many years now, the use of soy has been treated as quite controversial. Many researchers have tried to shed a little light on the problem of soy use and how it may endanger our health.

We cannot ignore the findings that most soy contains GMO[v], has a negative impact on the testosterone production[vi] within men due to the high levels of phytoestrogens found in soy, as well as the possibility that soy might be causing breast cancer within women, but are there any negative effects on our thyroid health as well?

While some doctors and researchers state that there is no reason to be worried about the use of soy and its potential negative effects on our thyroid health, there are some convincing findings.

The main problem about soy is the fact that it contains substances which are known under the term of goitrogens. Goitrogens have been proven to reflect negatively on the thyroid function because they tend to block the iodine absorption in the body.

As you probably know, iodine is an essential mineral when it comes to the maintaining a healthy thyroid function and production of the two thyroid hormones – thyroxine (T4) and triiodothyronine (T3) which contain iodine. In fact, goitrogens get their name from “goiter” which is the term that is being used to refer to an enlarged thyroid since goitrogens[vii] have been noticed to cause an enlargement of the thyroid gland commonly.

When consumed in large amounts, goitrogens are considered to alternate the thyroid function[viii].

Then we also have high amounts of flavonoids found in soy to be worried about. Flavonoids are a polyphenolic compound found in many plants, including soy. The use of flavonoids in our diet is also thought to be controversial, due to potential negative effects of these compounds on our bodies.

One of the potential negative effects that have been scientifically proven is the ability of the flavonoids to lower our TSH levels[ix]. TSH stands for Thyroid Stimulating Hormone, which is the hormone that is responsible for the production of the two thyroid hormones.

If the flavonoids reduce the TSH levels in our body, the thyroid hormone production is expected to drop as well, and we are exposed to the risk of hypothyroidism and many other health risks. Another study published in the Journal of Clinical Endocrinology also revealed that consuming around 16 gr of soy can triple the risk of developing hypothyroidism[x].

You may want to consume soy, but you have to be careful not to consume too much of it, exposing yourself to the previously discussed risks. We cannot ignore the fact that after all, soy is nutritious, so the trick is to be careful around it.

But what happens for the patients who have been diagnosed with a thyroid issue, especially hypothyroidism?

Should they steer clear from consuming any soy?

Should patients with hypothyroidism use soy in their diet?

When you are struggling with thyroid issues, it can be quite tricky to figure out which foods you should eat and which you should definitely avoid.

For example, consuming fresh fruits and vegetables is more than recommended, on the other hand, consuming dairy products and gluten is considered to only do you harm, by increasing the already present inflammation in your thyroid gland and worsening your present symptoms.

So, what happens with soy? Should you forget about its existence altogether or should you continue using it as before?

Patients with hypothyroidism are usually advised against the use of soy and any soy products as a part of their diet.

If soy lowers the TSH levels in your body, and with that, causes your already low thyroid hormone levels to continue reducing no positive effects are expected to happen. In fact, what it is expected to happen, is your symptoms getting worse, and with that, your overall health.

Soy can also prevent your thyroid hormone replacement medication from getting absorbed in your body. Soy, along with calcium, iron, gluten, and lactose, is one of the many compounds able to interfere with the absorption of your thyroid hormone replacement medication and cause you to require a larger amount of the medication over time.

By eliminating soy, and the other mentioned compounds, hypothyroidism patients have successfully reduced their need to take larger amounts of their thyroid hormone replacement therapy.

Should hypothyroidism patients avoid soy altogether?

So, knowing all of this, does this mean that hypothyroidism patients are supposed to avoid all soy products altogether?

No, of course not. But hypothyroidism patients are advised towards thinking twice before they consume too much soy in their diet.

The best advice that we can give you is to limit your soy consummation and make sure that you are taking enough iodine using natural sources, and thyroid support supplements if needed.[xi]

Hypothyroidism patients who are consuming too much soy, and too little iodine, and are even a target of iodine deficiency, are exposed at the greatest risk of their symptoms getting worse over time.

Act smart – limit your soy consummation, introduce enough iodine in your diet, and take your thyroid medication regularly, as instructed by your doctor and you will be able to preserve your thyroid function and health. If you have any additional worries about your diet and your thyroid health, please consult your doctor to get a professional opinion.


In conclusion, soy is a rather nutritional food product that, when chosen and consumed carefully, provides a lot of nutrients.

But there is still a reason to be careful about it, especially when someone has hypothyroidism.

Soy does not threaten to end your life, but it can make it harder to live, by causing your hypothyroidism symptoms to worsen.

Scientific studies recommend controlling your soy intake and taking your thyroid medication.


[i] Soy protein isolate Nutrition Facts & Calories. (n.d.)
Retrieved from

[ii] Butteiger, D., Cope, M., Liu, P., Mukherjea, R., Volpi, E., Rasmussen, B., & Krul, E. (2013). Soy, whey and caseinate blend extends postprandial skeletal muscle protein synthesis in rats. Clinical Nutrition,32(4), 585-591. doi:10.1016/j.clnu.2012.10.001
Retrieved from

[iii] Neacsu, M., Fyfe, C., Horgan, G., & Johnstone, A. M. (2014). Appetite control and biomarkers of satiety with vegetarian (soy) and meat-based high-protein diets for weight loss in obese men: A randomized crossover trial. The American Journal of Clinical Nutrition,100(2), 548-558. doi:10.3945/ajcn.113.077503
Retrieved from

[iv] Tokede, O. A., Onabanjo, T. A., Yansane, A., Gaziano, J. M., & Djoussé, L. (2015). Soya products and serum lipids: A meta-analysis of randomized controlled trials. British Journal of Nutrition,114(06), 831-843. doi:10.1017/s0007114515002603
Retrieved from

[v] Center for Food Safety and Applied Nutrition. (n.d.). Food from Genetically Engineered Plants – Consumer Info About Food from Genetically Engineered Plants.
Retrieved from

[vi] Weber, K. (2001). Dietary soy-phytoestrogens decrease testosterone levels and prostate weight without altering LH, prostate 5alpha-reductase or testicular steroidogenic acute regulatory peptide levels in adult male Sprague-Dawley rats. Journal of Endocrinology,170(3), 591-599. doi:10.1677/joe.0.1700591
Retrieved from

[vii] Eastman, C. J. (2018, February 06). Iodine Deficiency Disorders.

Retrieved from

[viii] Mccarrison, R. (1933). A Paper on FOOD AND GOITRE. BMJ,2(3797), 671-675. doi:10.1136/bmj.2.3797.671
Retrieved from

[ix] Maria Carolina De Souza Dos Santos, Gonçalves, C. F., Vaisman, M., Ferreira, A. C., & Carvalho, D. P. (2011). Impact of flavonoids on thyroid function. Food and Chemical Toxicology,49(10), 2495-2502. doi:10.1016/j.fct.2011.06.074
Retrieved from

[x] Tonstad, S., Jaceldo-Siegl, K., Messina, M., Haddad, E., & Fraser, G. E. (2015). The association between soya consumption and serum thyroid-stimulating hormone concentrations in the Adventist Health Study-2. Public Health Nutrition,19(8), 1464-1470. doi:10.1017/s1368980015002943
Retrieved from

[xi] Messina, M., & Redmond, G. (2006). Effects of Soy Protein and Soybean Isoflavones on Thyroid Function in Healthy Adults and Hypothyroid Patients: A Review of the Relevant Literature. Thyroid,16(3), 249-258. doi:10.1089/thy.2006.16.249
Retrieved from

We will be happy to hear your thoughts

      Leave a reply