Weight loss and weight gain rely on the balance of calories in, which are obtained through your diet, and calories out, which is the energy you burn throughout the day. Maintaining a healthy weight relies on a number of factors that balance your calories in and calories out including your diet, regular activity level, your genetics and your metabolism. The presence of an underlying medical condition can affect tissues throughout your body, leading to changes in your metabolic rate and the energy you burn each day, ultimately leading to weight gain.
One disease that can lead to weight gain is hypothyroidism, a dysfunction of your thyroid gland. This gland, found in your throat, acts as a site of synthesis for thyroid hormones. These hormones play a role in your metabolism, with the secretion of thyroid hormones boosting the number of calories you burn each day. Hypothyroidism often occurs when your thyroid becomes inflamed and your immune system begins to damage the gland, leading to a decrease in the production of thyroid hormones. As a result, your metabolism decreases, which often leads to unexplained weight gain. Other symptoms of hypothyroidism include sensitivity to cold, depression, and brittle nails and hair.
Polycystic Ovarian Syndrome
Another disease that can lead to unexplained weight gain is polycystic ovarian syndrome, also called PCOS. PCOS occurs due to a dysfunction of a woman's ovaries, leading to a hormonal imbalance. The ovaries serve as the site for the production of a number of sex hormones including estrogen and, to a lesser extent, testosterone. Women with PCOS develop a hormonal imbalance, leading to weight gain, or difficulty losing weight. The elevated levels of testosterone experienced by many women with PCOS also cause excessive hair growth and acne. If you suffer from these symptoms, consult with a physician to assess the health of your ovaries and address the possibility of PCOS.
Prolactinomas -- benign or non-cancerous tumors that secrete the hormone prolactin -- may also cause weight gain. Prolactinomas develop within the pituitary gland, a region in the brain that secretes a number of hormones, including prolactin. The growth of a prolactinoma increases the number of cells secreting prolactin, leading to abnormally levels of the hormone within your blood. In addition to weight gain, a prolactinoma can also cause a low sex drive, infertility, irregular periods in women and breast growth in men. Left untreated, the tumor may also lead to visual disturbances, as the prolactinoma's size interferes with the function of other nerve tissues.