You may need to take T3 hormone replacement as well as T4, even if your TSH is normal (see Chapter 4). You may be eating some food that interferes with thyroid hormone absorption, such as soy protein, around the time you take the thyroid hormone. Then again, maybe none of the above explain your weight gain. A study in the Journal of the American College of Nutrition in 1999 attempted to address this issue. The authors studied ten people who received radioactive iodine for hyperthyroidism. The researchers looked at the participants’ total food energy intake; their T4, T3, and TSH levels; and their height and weight at the time of treatment and at one, two, three, six, and twelve months afterward. The participants’ thyroid hormone levels declined in the first months of treatment but increased later. Even when thyroid hormone levels increased, the participants continued to gain weight. Interestingly, the average weight of the participants before the development of hyperthyroidism was about 170 pounds; at the time of treatment, 148 pounds; and after a year, about 168 pounds. Their final average weight was actually lower than their average weight before hyperthyroidism developed. The study concluded that weight gain after treatment of hyperthyroidism was initially due to a fall in the metabolic rate that accompanied the drop in thyroid hormone but later was due to food intake or lifestyle choices. Another study in the Journal of Clinical Endocrinology and Metabolism in 1998 showed where the weight gain occurs in the body when you receive treatment for hyperthyroidism. The researchers showed that most of the weight gain in the first three months occurred as fat in the waist area and in muscle tissue, whereas weight gain later on was in the fat under the skin. This study shows very clearly that the weight loss that occurred before treatment for hyperthyroidism was loss of lean tissue, the muscle mass — further proof that using excess thyroid hormone for weight loss leads to loss of muscle. Many people treated for hyperthyroidism gain more weight than they want to after treatment. In most cases, this occurs either because their thyroid hormone levels aren’t in the range they should be or because they don’t alter their eating and exercise habits after treatment. If you’re in this situation, keep in mind that you probably increased your food intake and decreased your activity level when your body was hyperthyroid. You need to make lifestyle adjustments after treatment in order to bring your body back to its healthy weight.
Avoiding iodine before thyroid studies The results of thyroid uptake studies are more valuable if the subjects avoid foods that contain iodine for a time before the test. The purpose of most such studies is to determine the size and shape of the thyroid and whether a given abnormality of the thyroid takes up iodine.