Most individuals with hyperthyroidism generally lose weight despite increased appetite and food intake although more than 10 percent of hyperthyroid people initially gain weight. Unfortunately, however, most everyone with hyperthyroidism gains weight after treatment of hyperthyroidism that results in permanent hypothyroidism. A large study at the University of Minnesota concluded that this is due to: a reduction in metabolic rate related to hypothyroidism and changes in food energy intake, which increased during the period of hyperthyroidism.
Another large Swedish study showed that weight gain following treatment was not related to the severity of hyperthyroidism or with the weight loss or weight gain that occurred before treatment for hyperthyroidism. Other factors that were studied and shown not to affect weight gain included smoking habits, cortisol level, treatment for hypothyroidism, cholesterol levels or trigylceride levels. This study concluded that women with hyperthyroidism should be informed about the risk of gaining weight after aggressive therapy and given early support regarding dietary and lifestyle changes.
An earlier study at the University of Minnesota showed that hyperthyroid people experienced weight loss result in a weight 83.9 percent of their weight before hyperthyroidism. By 96 months following the development of hypothyroidism, the average person weight 102.5 percent of their weight before becoming hyperthyroid. Many of these people were overweight before becoming hyperthyroid, which is probably related to the initial early hypothyroid phase seen in most people with hypothyroidism. The study concluded that the development of hypothyroidism is accompanied by weight gain.
Another recent study at Queen Hospital in England showed that the average person experienced a body mass index (BMI) increase of 8.49 within 24 months after treatment resulting in hypothyroidism. This study concluded that pre-existing obesity, and prior weight loss during hyperthyroidism were risk factors for weight gain, and that weight gain after hypothyroidism tended to increase with time. Patients who became permanently hypothyroid, despite proper treatment, gained the most weight.
There are no long-term studies relating exclusively to people treated only with anti-thyroid drugs. However patients treated with antithyroid drugs who were included in these studies were less likely to gain weight. Those who gained weight while on anti-thyroid drug therapy did not have trouble losing weight once they achieved remission.
Because weight gain is likely to occur in people who become hypothyroid, it’s important to incorporate exercise and correct any nutritional deficiencies that contribute to food cravings. While most people who are hypothyroid tend to crave salty foods, a number of people also crave sweets when they are hypothyroid. It is also important for hypothyroid individuals to make sure that they are on adequate thyroid replacement hormone. Tests for both FT4 and FT3 are essential for making sure that the right type and dose of thyroid replacement hormone are prescribed. For many people, T4 only (levothyroxine) is insufficient, and preparations containing T3 are needed.
