Unexplained weight loss, or losing weight without trying — particularly if it's significant or persistent — may be a sign of an underlying medical disorder.

The point at which unexplained weight loss becomes a medical concern is not exact. But many doctors agree that a medical evaluation is called for if you lose more than 5 percent of your weight in six months to a year, especially if you're an older adult. For example, a 5 percent weight loss in someone who is 160 pounds (72 kilograms) is 8 pounds (3.6 kilograms). In someone who is 200 pounds (90 kilograms), it's 10 pounds (4.5 kilograms).

Your weight is affected by your calorie intake, activity level, overall health, age, nutrient absorption, and economic and social factors.

Usually, an unrecognized cancer will have other symptoms or abnormalities of laboratory tests, in addition to unexplained weight loss.

Potential causes of unexplained weight loss include:

1. Addison's disease (adrenal insufficiency)
2. Cancer
3. Celiac disease
4. Changes in diet or appetite
5. Changes in sense of smell
6. Changes in sense of taste
7. COPD
8. Crohn's disease
9. Dementia
10. Dental problems
11. Depression
12. Diabetes
13. Heart failure
14. HIV/AIDS
15. Hypercalcemia
16. Hyperthyroidism (overactive thyroid)
17. Hypothyroidism (underactive thyroid)
18. Medications
19. Parkinson's disease
20. Peptic ulcer
21. Substance abuse (alcohol, cocaine, other)
22. Tuberculosis
23. Ulcerative colitis

Causes shown here are commonly associated with this symptom. Work with your doctor or other health care professional for an accurate diagnosis.

Source: mayoclinic.org

Your doctor will work with you to try to determine what's causing the weight loss. At first that will involve a thorough history, a physical examination and basic laboratory testing. Full body scans to look for hidden cancers are not usually helpful unless some other clue points in that direction.

Sometimes, if the basic evaluation is negative, watchful waiting for a few months is a reasonable next step. You may need a special diet to prevent further weight loss or to regain lost pounds.

Source: mayoclinic.org