For many years now, a theory has been circulating that links certain foods with low thyroid hormone levels. I’ve been asked about this link on several occasions by patients on thyroid medication.
The theory states that, in those with pre-existing thyroid dysfunction, certain foods cause a shift downwards in thyroid levels by being goitrogenic.
What is goitrogenic?
When a substance is goitrogenic, it leads to less thyroid hormone production by interfering with iodine uptake of the thyroid gland, located in our lower neck area.
Which Foods Are Believed To Be Culprits?
A short list of the foods believed to be goitrogenic:
soybeans and soy products (including tofu, soy milk, and some mayonnaise and salad dressings)
Where is the Proof?
Unfortunately, in my search for a good, reliable human study, I did not come across any. The closest to one was an extract from the Journal of Nutrition, dating back to 1956, titled Studies on Goitrogenic Agents in Food. The findings were interpreted from studies done on rabbits, rather than humans.
How Do These Foods Possibly Affect the Thyroid?
These foods may become goitrogenic only when consumed in large amounts.
Not only this, but they usually affect your thyroid only when your iodine intake is low as well, which is a rare occurrence in first world countries like the United States.
Iodine is normally found in small amounts of salt, as well as seaweed, kelp, fennel, Jerusalem artichokes, seafood, eggs, yogurt and milk, among other food items.
In addition, this effect may occur only when these vegetables are consumed raw.
Any cooking process, such as steaming, sautéing, or roasting, eliminates the potential for thyroid involvement. Some sources also point to shredding as another method leading to a decrease in goitrogenic effects (a 75% decrease).
Take Home Message
For now, I did not find evidential proof that links these food items to low thyroid hormone levels. I would absolutely continue encouraging my patients to eat super healthy foods like those listed in the list of goitrogens, but, like anything that’s ingested, moderation is important.
I still firmly believe in a diet that’s filled with fruits and vegetables, and the latest evidence in heart health seems to support that in pointing toward either a Mediterranean or plant-based diet.
You can read guest blog post, Would You Like A Burger With Your Bypass, for a cardiologist’s take on plant-based diets, written by friend and colleague Robert Ostfeld, MD.
In this day and age, in which people are obsessed with their health (which makes me happy to a large degree), and there is access to so much on social media, it is important to be weary of what’s out there. It’s also wise to remember that too much of a good thing is not always wise. Be aware of everything that goes into your body and of quantities.
Be smart about what you eat, and always discuss with your doctor or nutritionist before taking on a big change.