Introduction There have been different concerns on the relationship between hypothyroidism which is the underactiveness of the thyroid gland which cause an insufficient thyroid hormone production and weight gain/ obesity. This is due to the fact that hypothyroidism affects the metabolism calories and is frequently irreversible and progressive Main Discussion There are two types of hypothyroidism; the subclinical or mild hypothyroidism and overt hypothyroidism. The subclinical hypothyroidism state is where the concentration of TSH (Thyroid Stimulating Hormone) is elevated above the reference or normal range and the thyroxine is standard. The overt condition is where the thyroid stimulating hormone is above normal range and the thyroxine is below the range Nilsson (2007). Research shows that 2 to 5 percent of those people with subclinical or mild hypothyroidism condition do not necessary lead to overt hypothyroidism. This is because of the treatment of the condition at early stages. Hypothyroidism was first identified in the nineteenth century after an operation being done on the thyroid gland was performed; there were swellings of the face, hands and other eyes. After much analysis by the doctors, they realized that this was caused by the lack of thyroid hormones that are produced by the thyroid glands. A number of research studies have been done to try and ascertain if really this relationship should be a concern or is just a myth. Experiments have been done to patients with hypothyroidism to determine the cause of the condition. A person with hypothyroidism produces less thyroid hormone making the body functions and metabolism to be slow. This can have an effect to the normal metabolic function of the body. Hypothyroidism is a common type of thyroid dysfunction in the United Sates of America with up to five percent of the population having the problem. According to “the survey by National Health and Nutrition Examination of 1999 to 2002, 4,392 individuals are reported to have hypothyroidism (Centers for Disease Control and Prevention). Out of this population, women are the more affected population and more likely to be affected compared to men. Among women, older women are more likely to suffer from hypothyroidism with about twenty percent of those above 60 years have hypothyroidism. For the cases of hypothyroidism which are caused by iodine deficiency, the prevalence is about 2 to 5 percent and it increases to 15 percent for those who are more than 60 years. Research done by Verma, et all (2008) showed that those people with overt hypothyroidism are more overweight considered to those with subclinical hypothyroidism. The survey by “the National Health and Nutrition Examination” also shows that in those who have hypothyroidism both overt and subclinical hypothyroidism, whites are the ones with the higher percentage of 5.1 percent then Mexican Americans. The prevalence was lower in African American with a percentage of about 1.7 percent. Hypothyroidism which affects the thyroid glands is caused by a number of factors. One of the causes is the thyroid gland swelling leading to the damage of cells in the thyroid gland thus incapable of producing the require amount of thyroid hormone. Also thyroid surgery can causes hypothyroidism. These occurs because during the surgery, a sec