The endocrine system affects nearly every cell and organ in the body. The endocrine system is comprised of glands that emit chemicals controlling many bodily functions, including cell growth and development, mood, sexual functions, and metabolism. Metabolism is the process of converting fuel from foods into energy for the body to function.

Though the endocrine system is comprised of many glands, all of which work together in a properly functioning endocrine system, it is the thyroid gland that directly effects metabolism. The thyroid is the portion of the endocrine system responsible for secreting hormones that control the rate at which the body’s cells burn fuel for energy. The more hormones the thyroid produces, the faster the chemical process of converting fuel to energy occurs.

In a normal, healthy endocrine system, all the glands produce the right amount of chemicals for the body's needs. Sometimes, the glands of the endocrine system do not work normally. In the case of the thyroid, people may have either an overactive or an underactive thyroid. An overactive thyroid is a condition called hyperthyroidism, and an underactive thyroid is known as hypothyroidism.

An overactive thyroid produces too much of the thyroid hormones and causes the body’s metabolic rate to increase. Though people suffering from an overactive thyroid might lose weight even when they eat more, other symptoms may be more severe. These include fatigue, depression, a fast or irregular heart beat, and insomnia. Conversely, an underactive thyroid does not produce enough of the thyroid hormone, which causes the metabolic rate to slow. People with an underactive thyroid may gain weight or have difficulty losing weight, along with other symptoms similar to those of hyperthyroidism.

Many people with a previously healthy endocrine system may develop irregular thyroid function with age. Since the thyroid directly effects metabolism, which is directly linked to weight, a sudden change in weight generally prompts a thyroid check. A physician can help monitor your thyroid health with routine physicals and blood work. If you are experiencing symptoms of thyroid dysfunction, you should consult your doctor.