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Sudden and unexpected weight loss is usually a manifestation of an underlying disease. It can also happen as a consequence of a psychological condition. In any case, you should talk to your doctor.

It is normal to lose a few pounds now and then, but if you have lost more than 10 pounds or more than five percent of your body weight over a period of 6-12 months without dieting or exercise then this is a considered to be sudden weight loss and you should make an appointment with your doctor.

What Are The Causes Of Sudden Unexpected Weight Loss?

Sudden weight loss is a symptom, not a disease in itself. There are a number of diseases that can cause sudden weight loss.  

Cancer: Unexplained weight loss may be one of the first signs of cancer. Cancers that most commonly present with weight loss include stomach cancer, lung cancer, pancreatic cancer, esophageal cancer and leukemia. The cancer cells consume energy and change the metabolism and immune system of the body leading to weight loss and fatigue. This is called cachexia. It is often the first noticeable symptom of cancer.

Hyperthyroidism: This is one of the most common causes of sudden weight loss. An overactive thyroid produces excess levels of thyroid hormones (Thyroxin and T3), which increase the metabolism of the body. This in turn increases the energy expenditure, resulting in weight loss. This condition is very common in middle aged women.

Psychological Conditions: Certain psychological conditions can cause sudden weight loss. Depression is a common psychological disorder that can result in significant weight loss. Five percent of body weight can be lost within a month in depressed patients. Persistent stressful events can lead to sudden weight loss, but weight returns to normal after the stress is over. Anorexia nervosa is an eating disorder in which a person doesn’t eat in fear of getting fat. It is more common in females, but make no mistake: men get eating disorders too.

Malnutrition:  Malnutrition commonly causes sudden weight loss in children and elderly people, especially in developing countries. Besides a lack of access to food, a loss of appetite and conditions that prevent food entry into esophagus can also result in weight loss. Examples include Dysphagia (Painful swallowing), painful mouth sores and loss of teeth.

Stomach Ulcers: Stomach ulcers can interfere with the process of digestion which leads to defective absorption of food from the gut resulting in weight loss.

Drugs and Alcohol: Sudden weight loss is a side effect of certain medications. It also happen as a consequence of misuse of alcohol and recreational drugs. 

Persistent vomiting: Conditions that cause persistent vomiting (for example pyloric stenosis, alcohol misuse and hiatus hernia) lead to weight loss. In pyloric stenosis the lower end of stomach is contracted and food cannot go down, causing persistent vomiting.

Malabsorption: Celiac disease (gluten allergy), Crohn’s disease, chronic pancreatitis, intestinal hyper motility and gastrointestinal infections cause persistent diarrhea and decrease absorption of the food leading to weight loss.

Diabetes: Diabetes is characterized by insufficient levels of insulin. When there is a lack of insulin, glucose cannot enter the cells, where it would be used up as energy. The body starts to burn fat and muscles for energy instead. This is the basis of weight loss in diabetics.

Addison’s disease: Also called adrenal gland insufficiency, Addison's disease is a condition in which hormone secretion is reduced.

Chronic Inflammatory Diseases: Inflammatory bowel disease, systemic lupus erythematosus (SLE) and rheumatoid arthritis can cause sudden weight loss.

Chronic infections: Infections like HIV and Tuberculosis cause sudden weight loss. Parasitic infestations are another common cause in children.

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