Your thyroid gland's main function is to produce the hormones that cause your body to burn calories. Surgical removal of the thyroid will cause major, lasting changes to your body's metabolism.
Partial thyroidectomy (thyroid removal) is the treatment of choice for some hyperthyroid patients. Because a thyroid gland in overdrive typically causes weight loss, it makes sense that appropriate treatment will result in regaining some or all of the weight you lost while you were ill.
Your doctor may recommend a thyroidectomy if you have thyroid nodules that are suspicious for malignancy. If it turns out that you have thyroid cancer (which typically has a very high cure rate), your treatment will usually involve removal of the entire gland. If the tumor(s) are benign, then you may have only a partial thyroidectomy.
Thyroid Hormone Replacement
If you have a partial thyroidectomy, your doctor may not prescribe any thyroid replacement medication afterward, as your remaining thyroid tissue is expected to continue producing adequate amounts of hormone. However, if you had your thyroid removed due to cancer, you will take a thyroid hormone pill daily--not only to replace what your body can no longer produce, but to deter the pituitary gland from making thryoid-stimulating hormone (TSH), which may encouarge tumor growth.
Know Your Numbers
After surgery, your thryoid medication should replicate the function of a healthy thyroid gland. You will have blood tests to ensure that you are taking the correct dose. Your doctor should measure your TSH, free T3 and free T4 levels. If any of these is outside the normal range, you may experience symptoms of hypothyroidism, especially weight gain.
Diet and Exercise
We gain weight when our caloric intake exceeds the number of calories we burn. After surgery, it may take time to optimize your dose of thyroid hormone replacement. You may also gain weight if you alter your exercise routine during recovery.
Unfortunately, weight gain is a fairly common experience following thyroidectomy. Don't let your doctor tell you that it is a coincidence that this began at the moment your body's metabolism was irrevocably altered. Your doctor should base your thyroid medication dosage on your symptoms and complete clinical picture, not just your TSH number.