Severe weight loss generally refers to weight loss that causes a person to be underweight by 15 or more pounds. Causes for unexplained weight loss range from minor to life-threatening, including mental conditions such as anorexia and physical causes such as autoimmune disease or cancer.
Loss of Appetite
Loss of appetite is one of the most common causes of weight loss. Inflammatory bowel diseases are a common physical cause of appetite loss. Conditions in this category include ulcerative colitis, Crohn’s disease, celiac disease and irritable bowel syndrome, all of which are caused by inflammation in the digestive tract. Gastric ulcers may also make eating difficult and impair absorption of vital nutrients.
Anorexia and bulimia nervosa are two eating disorders that often lead to excessive and rapid weight loss. Both disorders have psychological causes that can contribute to appetite loss. Other mental illnesses that can cause weight and appetite loss include severe depression, anxiety and body dysmorphic disorder.
Malnutrition occurs when inadequate amounts of essential nutrients are consumed or absorbed by the body. Like appetite loss, malnutrition can be caused by either physical or psychological factors.
Celiac disease—a condition that causes destruction of the small intestine when gluten is ingested—is a common cause of malnutrition. According to Celiac.com, one in 133 people suffers from celiac disease, but only one in 4,700 is diagnosed with the condition. People with untreated celiac disease often have difficulty absorbing nutrients such as the B vitamins and may experience extreme weight loss.
Socioeconomic factors, such as lack of access to healthy foods, often cause malnutrition, as do psychological disorders such as compulsive dieting, anorexia and bulimia nervosa.
Weight loss can sometimes be caused by certain medications or illegal drugs. Stimulants such as cocaine or amphetamine are known to cause appetite loss and speeding of metabolism, which can cause drastic weight loss in those who abuse the substances. Alcoholism may also lead to weight loss by suppressing appetite or causing intestinal problems that interfere with nutrient absorption, as can opiate addiction.
The decongestant pseudoephedrine and the common stimulant caffeine can sometimes cause weight loss. Though not usually severe, use of certain prescription antidepressants can contribute to weight loss in some people.
Illness and Disease
Rarely, weight loss may be caused by a serious disease such as cancer or AIDS. Some cancers cause weight loss by stealing glucose and other nutrients from the body and inducing appetite loss. AIDS wasting syndrome is an effect of late-stage HIV disease that results from appetite loss, chronic diarrhea and vomiting caused by the disease.
Kidney disease, cirrhosis of the liver and autoimmune diseases such as lupus and multiple sclerosis are also known to cause severe weight loss in some people. Weight loss also can be a symptom of hyperthyroidism or Graves' disease.
Extreme, unexplained weight loss can sometimes signal a serious disease. If you experience sudden appetite or weight loss, consult a medical professional to rule out potentially life-threatening conditions.