The thyroid is a gland located in your neck just behind the larynx that produces hormones important to the regulation of growth and metabolism. When the thyroid gland is either overactive or underactive, metabolism is affected. Underactive thyroid is known as hypothyroidism.
Metabolic Changes
Altered metabolism is one of the significant effects of underactive thyroid. In fact, hypothyroidism can cause a metabolic reduction of 15 to 40 percent. Your basal metabolic rate is the amount of calories your body burns at rest. If your metabolism is reduced -- whether it happens gradually or suddenly -- and your diet remains the same, you will gain weight.
Weight Gain
According to "Obesity and Metabolism," 54 percent of subjects with overt hypothyroidism report weight gain compared with only 13.8 percent of control subjects. Because hypothyroidism often has a slow and insidious onset, it often goes undiagnosed. Unexplained weight gain may be one of the first noticeable symptoms and therefore the impetus for testing thyroid hormone levels to screen for hypothyroidism.
Causes
There is no single cause for hypothyroidism. Iodine intake is one of the known causes of hypothyroidism. Ironically, both inadequate and excess intake of iodine can result in hypothyroidism, but in both cases the iodine imbalance must be quite severe. Several types of pharmaceuticals, including antipsychotics, can cause hypothyroidism as a side effect. Other causes include thyroid surgery, radiation therapy, pregnancy and autoimmune disorders. Even the treatment for hyperthyroidism can overbalance and lead to hypothyroidism.
Treatment
Doctors typically prescribe synthetic hormone replacement therapy to treat hypothyroidism. Dietitians complement the drug therapy with a reduced-calorie diet to reverse the weight gain that patients who have hypothyroidism frequently experience. While calorie reduction is necessary, it is also important not to cut calories below your metabolic needs because of the risk of further depressing your metabolism. Your dietitian can help you determine the diet that is right for you.
References
- "Encyclopedia of Human Body Systems, Volumes 1-2"; Julie McDowell; 2010
- "Nutrition and Diagnosis-Related Care: Sixth Edition"; Sylvia Escott-Stump; 2008
- "Obesity and Metabolism"; Márta Korbonits; 2008
- Mayo Clinic; Hypothyroidism (Underactive Thyroid); June 2010
- "Harrison's Endocrinology, Volume 323"; J. Larry Jameson; 2006
- "Endocrinology and Metabolism"; Pauline Camacho; 2010
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