Did you know that certain foods can actually DAMAGE your thyroid? These foods should be avoided like the plague if you have thyroid problems, low thyroid function, hypothyroidism, and even Hashimoto's thyroiditis. And, by the way, these foods have several studies which show how they can damage and negatively harm your thyroid. They work by either blocking thyroid function, causing inflammation, or indirectly affecting your thyroid. Thyroid foods to avoid | thyroid foods.