Foods to consider avoiding with an underactive thyroid

Photos: Santeri Viinamäki, Rainer Zenz, Irene Kredenets. Design: BOOST Thyroid

Photos: Santeri Viinamäki, Rainer Zenz, Irene Kredenets. Design: BOOST Thyroid

What you eat massively influences your health—especially if you have an autoimmune condition. In fact, your diet can actually trigger Hashimoto’s.

It’s important to be aware of possible food sensitives you may have, as they can cause damage to your gut—this is considered the first step in developing autoimmunities. And once you have Hashimoto’s, certain foods can trigger troublesome flare-ups.

In addition to processed foods typical of the Western pattern diet, below are foods that commonly cause issues for people with an underactive thyroid and Hashimoto’s, as well as for those at risk of developing hypothyroidism.

Common foods that negatively affect people with Hashimoto’s

  • Nightshades

This vegetable food group includes tomatoes, potatoes, peppers, and potatoes (but not sweet potatoes). The problematic nature of nightshades are its compounds lectins and alkaloids. They’re actually considered antinutritional as they can bind to your gut, disrupt digestion, and cause ongoing inflammation (1).

  • Certain legumes and beans

    Lectins are also found in soybeans, kidney beans, Escumite beans, and french beans. However, cooking legumes and beans well will destroy lectins and make them safer to eat (1).

  • Soy

Beyond lectins, for some people soybeans can mess with thyroid health by disrupting iodide uptake and blocking zinc from functioning (2). Soy also contains isoflavones—the main active component of soybeans (similar to the hormone estrogen) that produces both hormonal and non-hormonal effects (3).

  • Animal milk

This dairy drink contains a very high concentration of antigens and saturated fat—these substances promote inflammation (4). Animal milk also shares proteins that are very similar to human proteins, including some found in the thyroid, which can cause an autoimmune reaction.

  • Wheat, barley, and oats

You should eat a gluten-free diet if you have celiac disease, gluten sensitivity, and/or a wheat allergy. And if your symptoms resolve when your diet is gluten-free, you might have a non-celiac gluten sensitivity (5-8). Gluten’s component gliadin is toxic for some people as it can cause damage to the gut, which  leads to inflammation that can trigger a chronic autoimmune reaction (9, 10).

  • Nuts

Although nuts can protect against inflammation, for a small percentage of people nuts cause autoimmune flare-ups (11, 12). This can happen because of nuts’ high protein content, which can cause a reaction from immunes cells in the gut.

Try an elimination diet for 4–8 weeks if you suspect certain foods are negatively affecting you. It’s best to eliminate different foods once at a time to really pinpoint what’s harming you. 

Track your symptoms and diet in BOOST Thyroid to help you understand your progress. After 4–8 weeks of elimination, slowly reintroduce the food to your diet to see if you have negative effects.


1. Lam SK, et al. Lectins: production and practical applications, 2011

2. Tran L, et al. Soy extracts suppressed iodine uptake and stimulated the production of autoimmunogen in rat thyrocytes, 2013

3. Khani B, et al. Effect of soy phytoestrogen on metabolic and hormonal disturbance of women with polycystic ovary syndrome, 2011

4. Melnik BC. Milk–the promoter of chronic Western diseases, 2009

5. Ludvigsson JF, et al. The Oslo definitions for coeliac disease and related terms, 2013

6. Sapone A, et al. Spectrum of gluten-related disorders: consensus on new nomenclature and classification, 2012

7. Volta U, et al. New understanding of gluten sensitivity, 2012

8. Ellis A, et al. Non-coeliac gluten sensitivity, 1978

9. Dicke WK, et al. Coeliac disease. II. The presence in wheat of a factor having a deleterious effect in cases of coeliac disease, 1953

10. Van De Kamer JH, et al. Coeliac disease. IV. An investigation into the injurious constituents of wheat in connection with their action on patients with coeliac disease, 1953

11. Zhao G, et al. Anti-inflammatory effects of polyunsaturated fatty acids in THP-1 cells, 2005

12. Yu Z, et al. Associations between nut consumption and inflammatory biomarkers, 2016

Diet, Lifestyle, BodyClar McWeeney