Diet and Hashimoto’s

The short answer: Hashimoto’s is not purely a thyroid disease. The immune system that attacks your thyroid is shaped to a large extent in your gut. That is why a Hashimoto’s diet, the way I work with it, starts in three places: your gut barrier, foods your body reacts to with a delay, and your gut bacteria. On top of that come cutting out gluten and cow’s milk completely, after a coeliac test, and topping up specific nutrients once they have been measured. Diet does not replace medication. But it reaches places no tablet can.

Why diet matters so much in Hashimoto’s

In Hashimoto’s, the immune system turns against your own thyroid, mainly against the enzyme thyroid peroxidase (TPO) and the storage protein thyroglobulin. Your tablet replaces the hormone your thyroid gradually stops making. It does nothing about the autoimmune process itself.

Almost 70 per cent of the immune system sits in the lymphatic tissue of the gut.^[1] What happens there every day helps decide whether your immune system settles down or keeps being triggered. Three mechanisms are central for me here.

1. The gut barrier: when your gut becomes more permeable

The lining of your gut is a fine protective wall. Its cells sit close together and are joined by so-called tight junctions, small seals between the cells. This wall decides what gets into your blood. When it becomes more permeable, more protein fragments, bacterial components and other irritants reach your immune system.

Gluten plays a special role here. Gliadin, part of the gluten protein, triggers the release of zonulin in the gut lining, a protein that loosens the connections between gut cells. In laboratory experiments this also happened in gut tissue from people without coeliac disease, though for a shorter time and less strongly.^[2] In a study of 40 people with Hashimoto’s, blood zonulin was higher than in healthy people; the authors interpret this as a sign of a more permeable gut.^[3]

Then there is a question that is much discussed in functional medicine: can antibodies against food proteins also cross-react with structures in the thyroid? In laboratory experiments, antibodies against thyroid structures such as thyroglobulin and deiodinase reacted with a range of food proteins. With TPO, the researchers found no such reaction.^[4] This is an early laboratory finding, not proof in humans. For me it is one more reason to always consider the gut in Hashimoto’s.

2. Reactions to food: the fast ones and the delayed ones

You know the classic food allergy: you eat a peanut and within minutes your lips swell. This reaction is mediated by IgE antibodies and is usually easy to pin down.

Reactions that only show up one to three days later are much harder. You eat something on Monday and feel exhausted, foggy or bloated on Wednesday. The symptoms are vague: tiredness, poor concentration, headaches, irritated skin, digestive trouble. Hardly anyone links them to what they ate two days earlier. In my coaching I often see delayed reactions like these in women with Hashimoto’s.

Many women hope for a blood test here. But the widely sold IgG food tests don’t help: the European Academy of Allergy and Clinical Immunology considers them unsuitable, because IgG against a food tends to show that your body knows that food, not that it can’t tolerate it.^[5]

The more reliable way is your own body: leave foods out, observe, bring them back one at a time. I work with a three- to four-week break, then reintroduce each food on its own, one every three days, with notes on sleep, energy, digestion and skin. The second step is the more important one. Without reintroduction you only know that you feel better without several things, not which one bothers you.

3. Your gut bacteria: your second immune system

Trillions of microorganisms live in your gut. They help with digestion, make vitamins, train your immune system and influence how tight your gut wall is. A meta-analysis found altered gut bacteria in people with autoimmune thyroid disease: certain beneficial bacteria were less common, unfavourable ones more common.^[6]

What helps your gut bacteria is well researched:

• Variety: In an analysis of more than 10,000 participants, people who ate more than 30 different plants a week had more diverse gut bacteria than people who ate ten or fewer.^[7] Vegetables, herbs, nuts, seeds and spices all count.
• Fermented foods: In a randomised study, a diet rich in fermented foods increased the diversity of gut bacteria, and inflammation markers in the blood went down.^[8] Good choices are unpasteurised sauerkraut, kimchi and lacto-fermented vegetables. Fermented foods are high in histamine; if you don’t tolerate histamine well, leave them out.
• Fewer additives: In a controlled feeding study in healthy adults, the emulsifier carboxymethylcellulose, found in many processed foods, reduced the diversity of gut bacteria after just eleven days.^[9] It is worth checking the ingredients list.

Gluten and cow’s milk: my clear approach

In Hashimoto’s I recommend cutting out gluten and cow’s milk completely. Fully, not “a little”, because every portion of gluten restarts the irritation at the gut barrier.^[2]

The research supports going gluten-free. In a meta-analysis of more than 6,000 patients, 1.6 per cent of people with thyroid autoimmunity had coeliac disease confirmed by biopsy.^[10] In another meta-analysis, TSH and antibodies tended to fall on a gluten-free diet, most clearly in people with gluten intolerance.^[11] In a controlled study of 34 women with Hashimoto’s, six months without gluten lowered TPO and Tg antibodies; in the group that did not change their diet, nothing changed.^[12]

With cow’s milk, two things matter. In a study of 83 people with Hashimoto’s taking levothyroxine, 75.9 per cent had lactose intolerance; after eight weeks on a low-lactose diet, their TSH went down.^[13] And in my coaching I see many women react to the milk protein casein with bloating, irritated skin or a build-up of mucus. That is why I leave out cow’s milk entirely in Hashimoto’s, not just the lactose. Many women tolerate sheep’s, goat’s and buffalo milk better.

The foundation: Mediterranean, high in protein, steady blood sugar

Plenty of vegetables, olive oil, nuts, fish and little processed food: this foundation feeds your gut bacteria and keeps inflammation low. Add protein to every meal. Thyroid hormones are built from the amino acid tyrosine, and protein keeps your blood sugar steadier. My guide value in coaching: at least 25 grams of protein at breakfast, 30 to 40 grams at lunch, at least 25 grams at dinner.

The thyroid nutrients

Selenium: the form matters

Selenium sits at the active site of the enzymes that convert T4 into active T3, and in protective enzymes that shield the thyroid from the hydrogen peroxide produced when hormones are made.^[15,16] Selenium contributes to normal thyroid function. How well a supplement works depends on your starting level, the dose, the duration and the form.^[17]

A meta-analysis of 35 randomised studies confirms that selenium lowers TPO antibodies; the results of the individual studies vary widely, though.^[18]

In Hashimoto’s I work with sodium selenite, the inorganic form. In Gärtner’s placebo-controlled study of 70 women, TPO antibodies fell by just over a third within three months on 200 µg sodium selenite daily: afterwards they were at 63.6 per cent of the starting value. On placebo they fell by only 12 per cent, to 88 per cent of the starting value.^[19] So with selenium the drop was roughly three times as large.

I choose it because its effect is easier to control. The German Federal Institute for Risk Assessment (BfR) describes the difference like this: inorganic selenium is incorporated specifically into selenoproteins, the enzymes your thyroid needs, and your body regulates this process. Selenomethionine, the organic form, is instead incorporated non-specifically and without regulation into other body proteins such as albumin, and is not released as needed.^[20] Your blood level then rises, but it says less about how much selenium actually reaches the enzymes: in a randomised study, selenomethionine raised plasma selenium in a dose-dependent way, while the selenium-containing enzymes in the blood did not change.^[21] With sodium selenite I can dose precisely after testing, and in my coaching I see clearer antibody trends.

200 µg is a temporary measure. I have selenium measured in whole blood before and during supplementation; my guide value is 140 to 170 µg/l.

Iodine: selenium first, then iodine

No iodine, no thyroid hormones. But when hormones are made, the thyroid produces hydrogen peroxide, and selenium-containing protective enzymes break it down. If selenium is lacking, more iodine can put extra strain on the thyroid.^[15] So the problem is iodine without enough selenium. In a large Chinese study, a high iodine intake was also linked to higher rates of hypothyroidism and autoimmune thyroiditis.^[22] A review considers balanced selenium and an adequate, not excessive, iodine supply essential in autoimmune thyroiditis.^[23]

That is why I follow a fixed order:

1. Measure selenium in whole blood. If it is below 140 µg/l, I top up selenium first.
2. Measure iodine in urine. If iodine is lacking, I only add it once selenium is at a good level.
3. Increase iodine slowly and check TPO antibodies along the way.

Iodine from food is fine. With Hashimoto’s, always discuss iodine supplements and their dose with your doctor first.

Iron

The enzyme TPO contains haem and needs iron. Iron deficiency slows its activity; in your results it is mainly fT4 that drops.^[16,24] Empty iron stores are therefore more than an incidental finding in Hashimoto’s. You can read how to interpret your ferritin in “Ferritin in women”.

Vitamin D

In a meta-analysis of randomised studies, vitamin D lowered TPO antibodies in Hashimoto’s.^[25] I always have the level tested and correct a deficiency in a targeted way.

Marker	Lab reference (example)	My functional guide value
TPO antibodies	below 35 IU/ml	below 9 IU/ml; recheck after 3 and 6 months
Ferritin (with low CRP)	approx. 10–150 µg/l	from 100 µg/l (decision limit, IMD Berlin)[26]
Selenium (whole blood)	101–170 µg/l	140–170 µg/l; build up before iodine
Zinc (whole blood)	4.88–6.67 mg/l	6–7.5 mg/l
Vitamin D (25-OH-D)	adequate from 20 ng/ml (50 nmol/l)	50–70 ng/ml (125–175 nmol/l)
Iodine in urine	100–199 µg/l adequate (WHO, population level)	100–300 µg/l; supplement only once selenium is good

Lab reference: typical example values; your lab’s range applies. Functional guide values: experience-based values from functional medicine and my coaching, not official reference ranges.

If you take levothyroxine

Your tablet only works if it is absorbed in your gut. Coffee, calcium, iron, fibre, lactose and low stomach acid can all slow absorption.^[13,27] You can read how to time your tablet and what changes your dose requirement in “How to take levothyroxine properly”. Only your doctor should change the dose.

Patterns I often see in my coaching

Pattern	Typical signs	Where I start
High antibodies, unsettled gut	Raised TPO antibodies, bloating, alternating bowel habits	Coeliac test, then gluten-free and cow’s-milk-free, build up gut bacteria
Tired two days after eating	Exhaustion, brain fog, irritated skin with no clear trigger	Leave foods out and reintroduce them one at a time
Tablet dose right, energy not	Normal TSH, fT3 in the lower third, selenium below 140 µg/l	Selenium as sodium selenite after testing, lower inflammation
Took iodine, antibodies went up	Iodine supplement without a selenium test	Measure and build up selenium, pause iodine and discuss with your doctor
High antibodies, empty stores	Raised TPO antibodies, ferritin below 50 µg/l	Replenish iron, check gut and absorption

Patterns are signs from my coaching experience, not diagnoses.

How I work in coaching

1. Full testing: TSH, fT3, fT4, TPO and Tg antibodies, ferritin with CRP, selenium and zinc in whole blood, vitamin D, iodine in urine; and the coeliac test before cutting anything out.
2. Take the load off your gut: consistently gluten-free and cow’s-milk-free, a Mediterranean foundation, protein at every meal.
3. Find delayed reactions: leave foods out for three to four weeks, then reintroduce them one at a time.
4. Build up your gut bacteria: plant variety, fermented foods if you tolerate them, few additives.
5. Nutrients in the right order: selenium first, then iodine if needed; iron and vitamin D according to your results.
6. Review after eight to twelve weeks: symptoms, fT3 and antibodies compared. Then we adjust the plan.

Where to start

• My free self-check shows you whether your signs point more towards your thyroid, perimenopause or the stress axis. You’ll then receive the starter guide that matches your result; for the thyroid, that is my free thyroid starter guide with a list of the key blood tests and a plan for diet, micronutrients, stress and gut.
• Your free clarity call: 20 to 30 minutes on Zoom. Together we look at where you stand and which next step suits you.

Frequently asked questions

Read on

• Understanding your thyroid blood tests
• How to take levothyroxine properly
• Ferritin in women

This article does not replace medical advice. Diagnoses are made by your doctor; changes to medication belong in medical hands.

Sources

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