Updated March 11, 2015.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

It seems the whole world is trying to lose weight, yet unexplained weight loss can be frightening. We’ve all heard of someone who lost weight for no reason and it turned out to be something bad. What are some possible causes of weight loss, what questions might your doctor ask, and what can you expect as you and your doctor seek to determine the cause?

What Is Unexplained Weight Loss?

Unexplained weight loss is defined as the unintentional loss of at least 10 pounds, or 5% of body weight over a period of 6 to 12 months. This would be equivalent to a 200-pound man losing 10 pounds or a 130 pound woman losing 6 to 7 pounds.

Weight loss may occur because you are eating less, or because your body is using nutrients differently due to a change in your metabolism or the growth of a tumor.

When to See Your Doctor

If you are losing weight without trying it is important to make an appointment to see your doctor, even if you think there is an explanation for your weight loss.

Diagnosing Weight Loss That Isn’t Intentional

If you have unintentional weight loss, your doctor will first take a careful history and do a physical exam. Depending on her findings, she may recommend further tests and radiology studies. 

Questions Your Doctor May Ask

• When did you first notice that you were losing weight?
• How fast have you been losing weight?
• Have you made any changes in your diet or exercise schedule?
• Have you ever had weight loss like this before?
• How upsetting is the weight loss to you?
• Are you having any other symptoms such as palpitations, shortness of breath, jaundice (a yellowish discoloration of the skin), thirst, or a sensitivity to cold or heat?

• How would you describe your general health compared to, say, a year ago?
• Have you had screening tests recommended for someone your age such as a mammogram or colonoscopy, and what were the results?
• Have you had any nausea or vomiting? Do you ever make yourself vomit?
• Have you been constipated or had diarrhea?
• Have you felt depressed or stressed lately?
• Do you have any dental problems that pose difficulties with eating?
• Are there any illnesses that run in your family?

Tests Your Doctor May Order

After asking questions and examining you, your doctor may recommend further tests. Some of them include:

• Lab Tests – Tests commonly ordered include a complete blood count (CBC), electrolytes (metabolic panel), liver tests, kidney function tests, inflammatory tests (sed rate, C-reactive protein), blood sugar (glucose), urinalysis, and thyroid tests.
• Radiology studies – Such as a CT of your chest or abdomen.
• Procedures – Such as endoscopy or colonoscopy to evaluate your stomach and colon.

Causes of Unexplained Weight Loss

There are many reasons for unexplained weight loss, some serious, and some more of a nuisance.  In older adults (over the age of 65) the most common cause is cancer, followed by gastrointestinal and psychiatric conditions.  An overview of some causes include:

• Endocrine conditions – Such as hyperthyroidism (overactive thyroid), hypothyroidism (underactive thyroid), diabetes and Addison’s disease.
• Infections – Such as HIV/AIDS, tuberculosis, endocarditis (infection of the heart valves), and parasitic infections.
• Cancer – Weight loss may be the first signs of cancers such as lung cancer (especially adenocarcinoma of the lung), colon cancer, ovarian cancer and pancreatic cancer.
• Intestinal problems – Such as peptic ulcer disease, celiac disease, Crohn’s disease, ulcerative colitis, and pancreatitis.
• Heart failure
• Kidney failure.
• Chronic obstructive pulmonary disease - (COPD) – Such as emphysema.
• Oral concerns – Such as gum disease, tooth decay, mouth sores, or braces.
• Smoking.
• Eating disorders – For example anorexia nervosa and bulimia.
• Poor nutrition – Due to poor food choices, or finances that limit the purchase of food (starvation).
• Psychological conditions - Such as depression and anxiety.
• Medications – Nearly any medication may have weight loss as a consideration.  Medications may cause weight loss directly, or cause nausea and loss of appetite leading to weight loss.
• Drug abuse – Not only street drugs such as methamphetamine, but prescription medications like Adderall and over-the-counter drugs like laxatives may be abused.
• Neurological conditions – Such as Parkinson’s disease and Alzheimer's disease.

Treatment

The treatment of weight loss that isn’t intentional will depend upon the underlying cause or causes.

<sub>Sources:

Chen, S. et al. Evaluating probability of cancer among older people with unexplained, unintentional weight loss. Archives of Gerontology and Geriatrics. 2010. 50 Suppl 1:S27-9.

Gaddy, H., and K. Holder. unintentional weight loss in older adults. American Family Physician. 2014. 89(9):718-22.

National Institute of Health. MedlinePlus. Weight Loss – Unintentional. Updated 01/06/13. http://www.nlm.nih.gov/medlineplus/ency/article/003107.htm

Wu, J. et al. Evaluating diagnostic strategy of older patients with unexplained unintentional body weight loss: a hospital-based study. Archives of Gerontology and Geriatrics. 2011. 53(1):e51-4.</sub>