Foods that aggravate thyroid problems include soy, cassava and cruciform vegetables, reports Cleveland Clinic. Soy interferes with medications taken by hypothyroidism patients, while cruciform vegetables produce an ion that affects the thyroid's absorption of iodine. Cruciform vegetables also lead to hypothyroidism when taken in large amounts. Patients with thyroid issues should also avoid taking iodine and kelp supplements.
Doctors advise patients with borderline thyroids to avoid consuming soy, such as soy milk and edamame, on a daily basis, notes Cleveland Clinic. Root vegetables, such as cauliflower and turnips, do not worsen thyroid issues, but patients with underactive thyroids should avoid the root vegetable cassava, which releases toxins that affect an underactive thyroid.
While kelp is not bad for thyroid patients, its supplement form may affect thyroid function, as kelp supplements contain up to 500 micrograms of kelp in each capsule, explains Cleveland Clinic. The daily suggested consumption of kelp is between 158 and 175 micrograms, or about one kelp a day.
Iodine supplements cause negative effects to thyroid patients, as they prompt the thyroid to create excessive or inadequate hormone levels, according to Cleveland Clinic. While iodine deficiency is the major cause of thyroid problems across the globe, the normal consumption of iodine from food in the United States is enough for most people. The recommended daily intake of selenium supplements is below 200 micrograms per day.