In cases of hyperthyroidism or over active thyroid gland, the affected person tends to lose weight without decreasing his/her caloric intake. In fact, people with hyperthyroidism tend to have an increased appetite, yet they lose weight.

In cases of hypothryoidism or an under active thyroid gland, there would be an increase in weight despite the absence of concomitant increase in appetite or food intake.

Both condition are diagnosed based upon the clinical picture (we rely on a group of signs and symptoms), plus blood tests (we measure the thyoid hormones known as TSH and thyroxine, +/- more advanced tests if deemed necessary) and maybe ultrasound of the thyroid gland in case the physical examination reveals enlargement or the presence of nodules.

both conditions are treatable either with oral medications, and sometimes with other treatment modalities, depending on the case.