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Weight loss occurs when a person burns more calories, or energy, than he or she takes in. It may be deliberate or unintentional.

What is going on in the body?

A loss of weight is due to one of three factors:

• fewer calories are consumed
• more calories or energy are burned off during activity
• a person's basic resting metabolism speeds up

Weight loss may or may not be intended. Unplanned weight loss is often a sign of serious illness.

What are the signs and symptoms of the condition?

Weight loss through physical activity and eating a proper diet should not cause concern. Rather, the person usually feels healthier. Intentional weight loss through unhealthy means, such as smoking or misuse of diuretics, causes other health consequences.

Unintended weight loss is a cause for concern. In this setting, the healthcare professional will need more information, such as:

• How much weight has been lost?
• When did the weight loss start?
• Has the person's appetite or thirst level changed?
• Has the person's diet changed?
• Has the person's activity level changed?
• Has there been a change in the person's bladder or bowel habits?
• Has the person's mood changed?
• What medicines, drugs, herbs, or other substances is the person taking?
• What other medical conditions does the person have?
• Are there any other symptoms, such as fever or weakness?

What are the causes and risks of the condition?

• cancer, including colon cancer, lung cancer, cancer of the pancreas, or leukemia
• conditions that affect the ability of the intestines to absorb food and other nutrients
• diabetes, a condition that results in high blood glucose levels
• digestive diseases, such as inflammatory bowel disease or peptic ulcers
• hormone imbalances, such as an increased thyroid hormone level known as hyperthyroidism
• increased level of physical activity, due to exercise or manual labor
• infections, such as HIV or tuberculosis
• intake of fewer calories
• medicine or drugs, such as amphetamines, ephedrine, cocaine, heroin, or alcohol
• psychiatric conditions, such as depression, anorexia, or schizophrenia
• severe kidney, liver, or heart disease

Other causes of weight loss are also possible. Sometimes a cause cannot be found.

What can be done to prevent the condition?

For unintended weight loss, prevention is related to the cause. Avoiding the drugs that cause weight loss could prevent those cases due to drugs. Practicing safest sex can nearly eliminate the risk of sexually-transmitted HIV infection. Practicing safer sex can reduce, but not eliminate, cases due to sexually-transmitted HIV infection. Many cases of unintended weight loss cannot be prevented.

How is the condition diagnosed?

In some cases, the cause of the weight loss is obvious from the medical history and a physical exam. In other cases, further tests are needed. Blood and urine tests may be ordered to diagnose underlying health problems. X-ray tests may be done, such as a chest X-ray to look for heart or lung disease. An abdominal CT scan can be used to look for cancer of the pancreas or liver.

What are the long-term effects of the condition?

• blood clots, such as deep venous thromboses
• cancer
• death
• diabetes
• gallstones
• heart disease
• high blood pressure
• osteoarthritis, which is also called wear and tear arthritis, the most common type of arthritis
• varicose veins, which are enlarged veins often seen in the legs

Intentional weight loss through smoking can cause all the heart, lung, and other negative health consequences of tobacco use. Misuse of diuretics can cause dehydration with all its resulting consequences. Intentional weight loss that is part of an eating disorder such as anorexia nervosa can cause illness in nearly every body system, and is sometimes fatal if not successfully treated.

The long-term effects of unintentional weight loss are related to the cause. Cancer, diabetes, HIV, and severe heart, liver, or kidney disease are common causes of death. Many people who abuse drugs have long-term effects related to social, legal, and psychological problems from the drug abuse.

What are the risks to others?

Weight loss is not contagious. If infection is the cause of unintended weight loss, however, the infection may be contagious. HIV, for example, can be sexually transmitted. Tuberculosis can be spread through respiratory secretions.

What are the treatments for the condition?

Weight management plans are helpful for obese or overweight people who want to lose weight.

Treatment for unintended weight loss is directed at the cause. For example, a person with diabetes may need insulin injections or other medicines to control his or her blood glucose levels. Someone who is abusing drugs may need to enter a rehabilitation program. An individual with an infection may need antibiotics. A person with cancer may need surgery, chemotherapy, or radiation therapy.

What are the side effects of the treatments?

Side effects depend on the treatment used for weight loss. Medicines may cause allergic reactions or stomach upset. Surgery can be complicated by bleeding, infection, or allergic reactions to anesthetic.

What happens after treatment for the condition?

A person who loses weight from diet and exercise often feels healthier and happier. Someone with unintentional weight loss may be cured by treatment, such a person with depression. Others may die, such as those with advanced cancer, HIV, or severe liver disease.

How is the condition monitored?

Weight can be monitored at home and at every visit to the healthcare professional. Further monitoring is related to the cause. For example, a person with diabetes needs frequent blood tests to monitor his or her blood glucose level. Any new or worsening symptoms should be reported to the healthcare professional.