If you do, you should restrict your consumption of Brussels sprouts, cabbage, cauliflower, kale, turnips, and bok choy since research shows that digesting these veggies may impair the thyroid's capacity to absorb iodine, which is necessary for regular thyroid function. Other foods that contain high amounts of starch or sugar and that may need to be avoided by those with thyroid issues include bananas, barley, beans, corn, potatoes, peas, rice, and wheat. Thyroid disease can lead to an underactive thyroid (hypothyroidism). Eating too much processed food and not enough nutritious food is common for people with hypothyroidism because their bodies are starved of essential nutrients they need to function properly. People with hypothyroidism may also have higher-than-normal levels of insulin in their blood. Insulin is needed to transport glucose from our bloodstream into our cells for use as energy, so a high level of insulin indicates that someone's body is trying to control its blood sugar by storing more of it as fat. This is called hyperinsulinemia and can lead to obesity if the patient does not change their diet. People with hyperthyroidism have low levels of insulin in their blood while those with autoimmune thyroiditis have normal to high levels of insulin. Like those with hypothyroidism, those with hyperthyroidism tend to be obese due to excessive storage of glucose in muscles and liver.