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Thyroid health and how diet impacts it

Updated: Jul 14, 2023

Hormone health is a subject of much debate amongst personal trainers and health coaches. But in the medical world, where we regularly see true hormone dysfunction in its purest forms, from mild impairment all the way across the spectrum to full endocrine dysfunction, the factors that regulate hormonal health are well studied, well known and pretty simple to understand.

In a recent blog post, I reviewed the most important factors that determine your hormone destiny and they’re pretty easy to grasp. Genetics and lifestyle seem to determine whether or not you’ll have hormonal dysfunction, along with the occasional case of bad luck which accounts for the rest. You can read the blog post where I review hormonal health here.

For this week’s blog post, I wanted to dedicate a full article to thyroid health. “Why thyroid?” you might ask. Because my mom suffers from Hashimoto’s thyroiditis, which is the most common from of hypothyroidism, along with other relatives. Up to 5% of the population suffers from the disorder, along with another 5% who are currently undiagnosed. When the condition is developing under the radar, it’s called subclinical hypothyroidism and the incidence shoots up to 8% in women and 4.4% in men. Although this may not seem like a lot, I’m ready to bet that you know someone who has or will be affected. With almost 1 out of 10 women affected by this condition, I rarely, if ever, go a week without seeing someone with hypothyroidism. It seems that we are managing thyroid hormone replacements daily, or interpreting thyroid hormone tests. If this doesn’t make me an expert, I don’t know what does. Oh, and did I mention that I taught endocrinology in medical school for almost a decade, and have been teaching thyroid disorders to medical interns since 2007. In this course, I focus on overt and sub clinical hypothyroidism as well as hyperthyroidism. We review thyroid cancers and nodules, as well as thyroiditis. Now if this seems a little overwhelming, that’s normal. Today, I’ll review normal thyroid function and then summarize how dysfunction occurs. I’ll also make sure to connect the dots and discuss how diet and lifestyle can affect thyroid function. We’ll discuss the foods to eat, those to reduce and how to help prevent thyroid dysfunction from ever happening at all!

The Normal Thyroid

The thyroid is a small, 5 centimetre butterfly, or bow tie shaped gland located at the bottom of your neck, wrapped around the larynx, or voice box, or Adam’s apple. It produces two very important hormones that have very important impacts on every single aspect of your health. T3 and T4, or triiodothyronine and thyroxine, respectively, are the two main hormones produced by the thyroid gland. T4, the main hormone produced is then transformed in to T3 in peripheral tissues, which then exert its effects on cells. Proper thyroid function controls many metabolic and bodily functions, including body temperature and general metabolism.

To produce thyroid hormones, the thyroid gland needs iodine, an element found in what we eat and drink.

If we ingest too much iodine, the thyroid gland slows down production of thyroid hormones in a protective mechanism called the Wolff-Chaikoff phenomenon. In some pathological circumstances, the protective brake that is the Wolff-Chaikoff phenomenon gets stuck and hypothyroidism occurs. In others, excessive exposure to iodine, via food, supplements, disinfectants, intravenous contrast or medications, actually causes the opposite, which is excessive and unhindered production of thyroid hormones, leading to hyperthyroidism. This phenomenon, called the Jod-Basedow effect, must be well known and understood before recommending iodine dosing or thyroid supporting supplements. I’ve seen and heard of horror stories from patients having these practices suggested by their « health coaches ». Always talk to your healthcare provider before starting iodine or thyroid impacting meds or supplements. That’s even more important if you have a personal or family history of thyroid disease.

Thyroid function is directly impacted by its main stimuli coming from the pituitary gland, a small gland located at the base of the skull. The pituitary secretes TSH, thyroid stimulating hormone, which makes the thyroid produce and secrete T3 and T4. If the thyroid stops functioning, TSH levels increases in an effort to encourage it to produce more thyroid hormones. If the thyroid is producing excessive thyroid hormones, like in Graves’ disease, then the TSH levels plummet. This is how we can measure and determine if thyroid dysfunction originates from the thyroid gland, or from the pituitary. If your TSH levels are high and your T4 is low, then you’re generally suffering from primary hypothyroidism, which means the actual thyroid gland is dysfunctional. This is by far the main medical condition affecting the thyroid. It’s called Hashimoto’s disease, which is a form of hypothyroidism caused by the auto-immune destruction of your thyroid gland. This condition is permanent and will require life long supplementation with thyroid hormones. If the auto-immune destruction of your thyroid gland is partial, maybe the rest of the gland will compensate, and in this case, you might suffer from sub clinical hypothyroidism, a type of « under the radar » hypothyroidism that could potentially be reversible, or might progress to full fledged hypothyroidism.

Most of the time, thyroid function is totally out of our voluntary control. Many and most people suffering from hypothyroidism have done nothing wrong. It’s not their fault.

It’s not their nutrition or lack of exercise. It’s multifactorial, with genetic, environmental and lifestyle choices all interacting with each other. That being said, in this article, I’ll review what actually is under your control, and how you can impact thyroid health through lifestyle choices. Proper thyroid function does require specific nutrients and we’ll review them in detail. Also, the main cause of hypothyroidism is an auto-immune process (remember Hashimoto?), so preventing auto-immunity through evidence based nutrition will definitely reduce risk as well.

The Abnormal Thyroid

The two main forms of thyroid dysfunction, or dysthyroidism, as stated earlier, are hypothyroidism and hyperthyroidism. Any condition affecting either the thyroid or the pituitary gland can cause hypo or hyperthyroidism. If the condition arises inside the thyroid itself, then we are talking about primary hypo- or hyperthyroidism (and both of these primary thyroid diseases can have many causes). If the condition arises from outside of the thyroid, either through pituitary dysfunction, or through exogenous thyroid hormone production for example, then we label it as secondary hypo- or hyperthyroidism.

Clinical presentations of these two conditions, hypo- or hyperthyroidism, are somewhat the opposites of each other. When hypothyroidism causes weight gain, hyperthyroidism generally causes weight loss. When hypothyroidism causes constipation, hyperthyroidism generally promotes bowel movements. Here’s a look at the symptoms and signs associated with hypo- and hyperthyroidism:

Nutrients Needed For Optimal Thyroid Health


Iodine plays a major role in thyroid hormone synthesis and thyroid hormones pretty much control most of the body's metabolic functions. Iodine deficiency, although rare since the advent of iodized table salt, is still possible in those eating a clean, low meat, low processed food and plant-predominant diet, even more so if they’re not consuming iodized salt. Iodine deficiency soon leads to hypothyroidism and if this occurs in the pregnant or lactating mother, or in young children, it can be disastrous. Those consuming a completely plant-based diet may be at a higher risk of having low iodine, and even iodine deficiency. There’s no reason that this should ever be happening in the modern world. People simply need to be educated on the matter. Iodine is easy to find on a plant-based diet, but you need to know where to look.

Iodine comes mainly from the seas and the oceans and is also found in the soil adjacent to them.  It is difficult to find in some plant foods, due to the poor quality of today's modern soils.  Iodine is found in certain seaweeds, like kelp, but not many people consume adequate amounts. It’s also found in fish, shellfish, dairy and eggs. Dairy isn’t a naturally great source of iodine, but the animal feed is fortified and sanitizing agents used by the dairy industry can also contain iodine. If you drink cow’s milk, iodine seeps in through the use of sanitizing products.  Cranberries and potatoes have very variable sources of iodine largely depending on the soil levels in which they were grown.  Table salt is iodized, meaning fortified, but most people on processed diets already eat too much and salt is linked to increases in blood pressure, heart disease and stomach cancer, and should be kept to 1500 - 2300 mg per day.  You can read my recent blog post about salt, sodium and all things Pink Himalayan rock salts here. One half to 3/4 of a teaspoon of iodized table salt per day will give you all the iodine you need.  Keep in mind that the salt used in most processed foods isn’t iodized. Nori sheets, like those used for making sushi, do contain upwards of 40-50 mcg of iodine, and are great sources. But be careful with iodine, too little and deficiencies are possible, but too much might trigger a Wolff-Chaikoff or Jod-Basedow phenomenon (as discussed in the « normal thyroid » section).

If you avoid table salt, remember that the alternatives, like Celtic salt, sea salt or pink Himalayan rock salt, aren't always iodized.  Try eating more marine plants, or you could consider supplementing.  The recommended daily dose is 150 mcg for adults of both sexes. I supplement by using a pinch of kelp powder. It’s barely noticeable and can be used in smoothies, soups or whichever way floats your boat. 1/16th of a teaspoon of kelp powder will cover your requirements, but remember that overdoing it might bring you close to the upper limit.


Selenium is another very important mineral that plays a major role in thyroid health. It plays important roles in converting T4 to T3, and also helps in the synthesis of glutathione, an antioxidant that helps lower oxidative stress in the thyroid. Luckily, a single Brazil nut a day provides all of the selenium you need! Other sources include whole grains, like whole grain pasta and brown rice, beans and seeds. Studies also suggest that having sufficient daily selenium intake is protective against other conditions, like acne, prostate cancer and pre-eclampsia.


Thyroid peroxidase, which we call TPO, is an enzyme (a type of protein) that oxidizes iodide into iodine in order to be incorporated into tyrosine, which then will lead to production of the two thyroid hormones, T3 and T4. Iron does play a role in allowing TPO to help produce thyroid hormones. Iron can be found in many plant sources, including legumes like lentils, beans and chickpeas, as well as whole grains, some dark leafy greens, as well as whole grains, pumpkin seeds and dried fruit, like figs, apricots and raisins.


Zinc also helps support thyroid function and immunity. Sources containing zinc include wheat germ, lentils, chickpeas, cocoa powder, oats, cashews, tofu and pumpkin seeds.

Recently, I had someone tell me that their healthcare provider (I believe this was her naturopathic doctor) suggested that she eat more red meat, dairy and eggs for thyroid health. Don’t get me wrong, I do understand where this recommendation is coming from. Red meat does contain iodine, as well as the other nutrients involved in proper thyroid function, but red meat is also classified as a Class 2a carcinogen by the World Health Organization. It’s also a very important source of saturated fat, cholesterol, heme iron and a major risk factor involved in the development of cardiovascular disease. One must remember that cardiovascular disease and cancer are the top two causes of mortality in North America, not thyroid disorders. Using red meat for thyroid health could be compared to stepping over dollars to pick up pennies, or eating McDonald’s french fries in order to boost vegetable intake. The important thing that people seem to forget, or ignore, is that cows get their iodine, iron, zinc and selenium from plants, not from meat. We can definitely keep our thyroids healthy by cutting out the middle man, in this situation the cow, and getting our nutrients either from plants directly, or from supplements. Increasing our risk of cancer or cardiovascular disease in order to promote thyroid health maybe isn’t the best way to go.

Nutrients Needed To Help Prevent Auto-immunity

We do have data on how plant-based diets can lower inflammatory parameters and epidemiological data suggesting that plant-predominant patterns of eating are associated with lower auto-immune disease rates, including Hashimoto’s thyroiditis. If you or someone you know suffers from hypothyroidism and must take lifelong thyroid supplements, then chances are that you or they suffer from Hashimoto’s, the auto-immune destruction of your thyroid gland. Eating a plant-predominant diet is definitely an evidence based way of lowering inflammation and auto-immunity and could help drastically reduce your chances of developing an auto-immune induced hypothyroidism. That being said, nothing is absolute and the primary causes that flick on the auto-immune switch are still poorly understood. My mother suffers from Hashimoto’s thyroiditis, the main cause of hypothyroidism, and because of this, I’m well aware of a certain genetic predisposition. Still, I’d rather not take any chances, so I’m keeping it plant-based! I’ve even published a review of the anti-inflammatory diet, the evidence based way of lowering inflammatory parameters and reducing your risk of auto-immunity. Read it here.

Goitrogens: Foods That Could Impact Thyroid Function

I recently had a patient who was already diagnosed with hypothyroidism tell me that she was told by her alternative care provider that she should avoid consuming soy, because it was a « thyroid blocker ». Now, that’s a pretty bold claim to make, and before telling someone to restrict a food or food group because of its thyroid blocking capabilities, one must understand the nuances. Firstly, foods don’t simply « block » thyroid hormones. Although some foods have been labeled as « goitrogenic », meaning that they’ve been labeled as capable of inducing goiter (an enlarged thyroid), one needs to understand the fine print. Secondly, we do absolutely need to pay attention to certain foods in some susceptible individuals, since some have been associated with the capacity of decreasing the absorption of iodine and other minerals associated with thyroid health. Let me explain. It’s no secret that certain compounds in plants, including fiber, oxalates and phytates have been shown to decrease the absorption of certain minerals. Other foods can limit iodine absorption, and also impede the uptake of iodine by the thyroid itself. These mineral “blockers” could even have protective effects, for example, by helping to reduce iron overload, which is highly inflammatory. Now, if you’re not paying attention to nutrient intake, specifically iodine, and you’re eating a whole bunch of foods that are known to reduce the absorption of iodine, like soy and cruciferous vegetables (cauliflower, cabbage, kale, broccoli and Brussel sprouts, just to name a few), then you might run into problems. In this situation, you may become deficient in iodine and run into thyroid dysfunction. The root cause here isn’t the « thyroid blocking » food, but the iodine deficient diet. If you get sufficient iodine in your diet, either via adequate plant sources or supplementation, then you have nothing to worry about and the same foods that are labeled as goitrogenic are actually amongst the healthiest foods on the planet. If you already suffer from hypothyroidism and are taking thyroid medication, have a conversation with your doctor. Soy and cruciferous vegetables, the same foods that some would label as « thyroid blockers » have been shown to reduce cancer, cardiovascular risk factors, and are excellent sources of fiber, vitamins, minerals, polyphenols, not to mention the preferred fuel source for the good gut bugs of our microbiome. Please, stop labeling food as « thyroid blockers » before understanding all of the nuances.

My Main Hormone Takeaways

Science does suggest we do a few things to help keep our hormones in check. You can read a more detailed article dedicated specifically to this subject here. Or you can simply choose to implement as many of these health hacks as you can: 

  • Choose whole or minimally processed foods as much as is practical for you.

  • Eat more fiber.

  • Try to get 80-90% of your daily calories from plants.

  • Aim for a healthy body weight.

  • Eat more soy products.

  • Consume ground flax seeds daily. Their lignans and omega-3 content have been shown to do many things, from lowering cancer risk, to lowering blood pressure.

  • A single Brazil nut provides the daily selenium you need.

  • A pinch of kelp powder will provide the iodine you need.

  • Eat a handful of nuts everyday. Their healthy fat content as well as mineral content contributes to overall hormonal health.

  • Spices and herbs, like turmeric, ginger, cinnamon, sage and parsley have high anti-oxidant and anti-inflammatory properties.

  • Avoid consuming foods in heated plastic containers to reduce hormone disrupting phtalates.

  • Supplement with vitamins B12 and D.

My Main Thyroid Takeaways

Adults need about 150 mcg of iodine per day, with children 9-13 years old needing about 120 mcg and kids from 1-8 years old needing about 90 mcg. Babies up to 1 year need about 130 mcg, and this period is crucial in the baby’s brain development. Plant-exclusive eaters are at an increased risk of deficiency if they don’t find iodine from iodized salt, seaweed, kelp, or supplements. At our home, we use iodized salt and kelp powder. To meet daily requirements of iodine through iodized salt alone, adults will need one half to 3/4 of a teaspoon. Children from 9-13 will need 1/3 of a teaspoon and young children from 1-8 will need 1/4 of a teaspoon. I personally use kelp powder. A measly 1/16th of a teaspoon, equivalent to a small pinch, will provide all of the iodine you need, about 150 mcg. At this small dose, kelp powder is tasteless and pretty much undetectable. Stay under 1/2 a teaspoon of kelp powder per day, since the upper limit of 1100 mcg in adults is easily attainable.

Basically, if you’re gonna remember only one thing, remember that adequate iodine intake and the overall quality of your diet are the main predictors of thyroid health. Genetics do increase risk, but lifestyle is often what flicks that genetic switch. My mother suffers from Hashimoto’s thyroiditis, the most common form of hypothyroidism, and I’ve voluntarily chosen to live the plant-based lifestyle, cause I know it’s my best chance to living my best life. If you want to learn about the interesting medical journey that brought me to living the plant-based lifestyle, check out my recent blog An intimate look at my medical and personal journeys here.

If you’re interested in learning how to transition towards the plant-based lifestyle, or the benefits associated with it, check out my free website There, you can even download my free recipe eBook, where you can find over 20 of my family’s favorite plant-based recipes. All of it is 100% free! Enjoy!

Look for me on the socials, @plantbased_dr_jules on Instagram and go like my Facebook Page, Plant-based Dr. Jules. If you’re looking for some fitness motivation and are curious to see what a plant-based athlete can accomplish, follow me, @maritimeninja, on my fitness account on Instagram or check out my fitness group on Facebook, called Maritime Ninja Warrior. I'm a two-time world championship qualified athlete and you can follow my fitness journey there! You can even access the resources section by becoming a member. It's free and there, you can download free resources like my plant-based recipe eBook!

You also check out my YouTube channel here for more tips and tricks on how to embark on a plant-based journey!

Thanks for reading


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