Goitrogens and thyroid health — the good news!
My patients with hypothyroidism sometimes ask about stories they’ve heard
in the news or seen on-line about the effects of certain foods on their thyroid
health. Soy is their most common concern, but broccoli, peanuts, strawberries, kale,
and other vegetables are also on this list. The message my patients hear, unfortunately,
is that if you have any sort of thyroid dysfunction, you shouldn’t consume
these foods — ever. And that’s a shame, because this all-or-nothing
approach means that women with thyroid problems remove healthy, nutritious foods
from their diet when they really don’t have to.
It’s true that there are certain foods that contain goitrogens, which
are compounds that make it more difficult for the thyroid gland to create its hormones.
However, the piece of the puzzle that’s missing in the advice to “avoid”
this food or that one because it contains a goitrogen is that you can limit or even
eliminate the harmful effects of these compounds in so many ways —
either by limiting the amount you consume, or by preparing the food in such a way
as to break down the goitrogenic compounds. Sometimes eliminating the goitrogen
is as simple as steaming your vegetables before you eat them!
So let’s look at what goitrogens are, where they occur in our food, and how
we keep them from affecting our thyroid function so we can enjoy our favorite healthy
foods without concern for our thyroid health.
What is a goitrogen?
Most goitrogens are naturally-occurring chemicals that are ingested in foods or
drugs. These chemicals can interfere with thyroid function in different ways. Some
compounds induce antibodies that cross-react with the thyroid gland; others interfere
with thyroid peroxidase (TPO), the enzyme responsible for adding iodine
during production of thyroid hormones. Either way, the thyroid isn’t able
to produce as many of the hormones that are needed for regulating metabolism (see
my article on nutrition and thyroid health for more on how this works).
For people with healthy thyroid function, the thyroid simply compensates and makes
more of the hormones as they’re called for. But in some people whose thyroid
function is already compromised, the thyroid gland may actually grow more cells
as it tries to make up for inadequate hormone production, eventually forming a goiter
(a swelling or enlargement of the thyroid gland).
What foods contain goitrogens?
You may be surprised by how many common foods contain goitrogenic compounds, but
the good news is, in most cases you don’t have to cross them off your grocery
list. Let’s take a look at some of them and discuss how you can keep them
in your diet, even if you have hypothyroidism.
Gluten. It may surprise people to see gluten at the top
of my list of potential goitrogens, but the truth is that gluten sensitivity contributes
to a wide range of autoimmune responses aside from celiac disease (the one for which
it’s best known). Gluten sensitivity has been found to go hand-in-hand with
autoimmune disorders such as type 1 diabetes, Addison’s disease, Sjögren’s
syndrome, rheumatoid arthritis, and autoimmune thyroid disease. I commonly recommend
that my patients consider eliminating gluten from their diets, particularly if they
already have an autoimmune disorder. If you have autoimmune hypothyroidism, you
might want to consider limiting your intake of wheat, barley, and rye, or even going
completely gluten-free (we have a lot more to say about this in our article on gluten).
I also suggest that women with autoimmune thyroid disease consider screening for
celiac disease, because undetected celiac can be one reason that women continue
to have hypothyroid symptoms despite higher and higher doses of thyroid replacement
If you’d like to keep gluten in your diet but you’re concerned about
your thyroid, try scaling back on how often you eat it. Be aware that gluten is
included in a great many processed foods, so it may help if you look for those varieties
that advertise as gluten-free. And instead of having wheat bread or baked goods
with your meal, consider substituting gluten-free grains or saving them for the
occasional treat. You may find after awhile that you don’t miss gluten nearly
as much as you may have thought (but if you find yourself craving bread or pasta,
it could be a sign of gluten sensitivity).
Soy isoflavones. Soy is a very healthy food that has been
demonized by various groups, something we discuss in our article on the soy controversy.
One legitimate concern these groups raise is the fact that soy does contain goitrogenic
compounds, specifically the soy isoflavone genistein. This compound, just
like thyroid hormones, accepts iodine molecules from the thyroid peroxidase (TPO),
which again, is the enzyme that also transfers iodine to the thyroid hormones. Some
researchers have suggested that genistein and similar isoflavones may compete with
thyroid hormones for iodine or alternatively may “block” the action
of TPO, but recent studies indicate that as long as an individual has sufficient
iodine in the diet, soy isoflavones do not adversely impact thyroid function.
“If one begins with poor iodine nutrition, removing goitrogens from one’s
diet will not restore iodine nutrition.”
— Dasgupta, P., et al. 2008. Iodine nutrition: Iodine content of iodized salt
in the United States. Environ. Sci. Technol., 42 (4), 1315–1323.
Other good news is that the goitrogenic activity of soy isoflavones can be at least
partly “turned off” by cooking or fermenting. With soy foods, you may
want to favor fermented, cultured, or otherwise “aged” soybean products
such as tempeh, soy sauce, miso, and natto. These methods of processing soybeans
alter the activity (goitrogenicity) of the phytochemicals they contain. If you do
eat whole soybean foods such as edamame or tofu, eat them cooked or steamed.
The goitrogenicity of soy can also be offset by pairing it with products containing
iodine. I tell my patients with thyroid problems that if they already eat soy products
and wish to continue, they should be sure to include additional iodide in the diet,
in the form of seaweed products such as kombu or nori. For people who don’t
already use soy regularly, I suggest that they simply continue whatever limited
usage they already have and not worry about it too much, as such small amounts aren’t
likely to impact the thyroid too greatly — but keep in mind that if you eat
processed foods containing certain soy-based additives like soybean oil or hydrolyzed
soy protein, they could be a “hidden” source of soy isoflavones that
many hypothyroid woman could probably do without!
So unless you have a true soy allergy, I wouldn’t worry too much about every
little soybean or soy shake you consume. More importantly, if you do include soy
in your diet and have concerns about your thyroid function, it’s worthwhile
to have your iodine levels checked by your practitioner, who can (if necessary)
offer you supplemental elemental iodide in amounts that are correct for your profile.
We also recommend that people with thyroid problems who consume soy regularly include
good dietary sources of selenium — and be sure to continue monitoring thyroid
hormone levels regularly with their practitioner.
Isothiocyanates. These compounds are primarily found in
cruciferous vegetables, such as cabbage, Brussels sprouts, broccoli, broccolini,
cauliflower, mustard greens, kale, turnips, and collards. Isothiocyanates, like
soy isoflavones, appear to block TPO, and they may also disrupt signaling across
the thyroid’s cell membranes. But no one would argue that these vegetables
are bad for you, given that they are filled with vitamins, minerals, antioxidants,
and a variety of nutrients we all need (aside from being delicious!). Women with
thyroid problems definitely should not avoid them — instead, enjoy them steamed
or cooked, as the heat alters the isothiocyanates’ molecular structure and
eliminates the goitrogenic effect.
Are there more? Maybe... Certain “potentially goitrogenic”
compounds are also present in small amounts in peanuts, pine nuts, millet, peaches,
strawberries, spinach, and cassava root, among others. I tell my patients who are
concerned about these foods that unless they’re consuming them in high amounts
on a continual basis, they’re not likely to have undue impact on their thyroid
health, because the possible goitrogens are present in such minute quantities.
I’d like to emphasize that these foods won’t pose a problem for people
with healthy thyroid function, nor will they be harmful when used in moderation
by those whose thyroid function is impaired, but excessive use of foods
containing goitrogens may trigger or exacerbate a thyroid problem. This is all the
more reason to make sure your diet contains a variety of delicious, healthy,
whole foods — we weren’t meant to eat the same thing over and over!
Enjoy your goitrogens with a sprinkling of common sense
I’m always dismayed when women are told they have to avoid a healthy food
when there isn’t a very good reason for it (a food allergy, for instance).
It would be a shame if women with thyroid problems avoided these goitrogenic foods
altogether, because most of what I’ve listed above contain beneficial micronutrients
and have strong value as healthy foods that support digestive, skeletal, cardiovascular,
and immune function. It just doesn’t make sense to deny the rest of our body
the benefits of these foods when the threat they pose to our thyroid is so slight
and can be eliminated so easily! So I suggest that we all use a little common sense
when it comes to goitrogens and our thyroids — steam, cook, or ferment your
vegetables to reduce the goitrogenic compounds, rotate your choices so that you’re
not eating the same foods every day, and above all, enjoy them as part
of a richly varied diet of wholesome foods.
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Last Modified Date: 05/27/2011
Principal Author: Marcelle Pick, OB/GYN NP