Weight gain is the increase in body weight due to an increase in fat, muscle mass, excess fluids, or other factors. It may be a natural result of over-consumption of food, a side effect or certain medications, or a symptom of an underlying medical condition. Around one in three people in the United States are considered overweight or obese.
Possible causes of weight gain include environmental or lifestyle factors, such as a sedentary lifestyle, poor diet, lack of sleep or stress; a hormone imbalance; or certain diseases and conditions, including Cushing’s syndrome or hypothyroidism.
In some cases, weight gain is desirable, for example in cases of malnutrition or when patients have certain eating disorders, such as anorexia nervosa.
Treatment of unwanted weight gain may involve lifestyle and dietary changes or treatment of the underlying cause. Certain medications are also available to promote weight gain. Drug classes used to encourage weight gain are cytostatic progestogens, cannabinoids, androstan derivatives, and insulin administration devices.