The thyroid is a small gland in the throat that produces two hormones that affect cells throughout the body. The thyroid helps set the body's metabolism; as a result, patients with a hypoactive thyroid may have decreased energy and are prone to gaining weight.
Physiology
The thyroid produces two distinct hormones, called T4 and T3. These hormones, according to Anesthetist.com, affects the amount of energy that cells use. T4 and T3 cause cells to make more of a protein called the sodium-potassium transporter, which pumps sodium into the cell and expels potassium. This protein requires large amounts of energy to work. Thus, the hormones produced by the thyroid increase the amount of energy that each cell uses.
Metabolism
The amounts of thyroid hormone in the body affect what is known as the basal metabolic rate, or BMR, as Thyroid.org explains. A patient's BMR is the amount of energy that the body uses when the patient is at rest. Patients with hypothyroidism have a lower BMR than normal, which means they burn less energy. Because energy in the body comes from food, patients with hypothyroidism burn fewer calories. These calories can then be stored as fat, leading to weight gain.
Activity
Patients with a hypoactive thyroid also tend to experience fatigue, the Mayo Clinic explains. Fatigue in turn makes them less physically active. Combined with the lower BMR, this makes it easier for patients to gain weight. In addition, a hypoactive thyroid can cause depression, which also is linked to less physical activity and therefore decreased burning of calories.
Diagnosis
Patients who are experiencing unexplained weight gain as well as other symptoms of hypothyroidism, such as fatigue or cold intolerance, may need to have their thyroid checked. A hypoactive thyroid, Medline Plus explains, can generally be diagnosed using blood tests. The level of T4 and T3 in the patient's blood will be measured. Another hormone, known as thyroid-stimulating hormone, may also be measured. Thyroid-stimulating hormone is produced by the pituitary gland and causes the thyroid to make more T4 and T3. Hypothyroidism can be caused by problems with the thyroid or as a result of the pituitary gland being unable to produce enough thyroid-stimulating hormone. If the problem is with the thyroid gland, the levels of thyroid-stimulating hormone will be elevated.
Treatment
Aside from changes in diet and exercise habits, many patients with a hypoactive thyroid can lose excess weight by having their thyroid problem corrected, Thyroid.org explains. In some cases, this involves taking synthetic forms of T3 and T4. With proper treatment, many patients will see their weight return to what it was before they developed thyroid problems.
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