Definition

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.

Causes

Unexplained weight loss has many causes, medical and nonmedical. Often, a combination of things results in a general decline in your health and a related weight loss. Sometimes a specific cause isn't found.

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:

• Addison's disease (adrenal insufficiency)
• Amyloidosis (buildup of abnormal proteins in your organs)
• Cancer
• Celiac disease
• Changes in diet or appetite
• Changes in sense of smell
• Changes in sense of taste
• COPD (chronic obstructive pulmonary disease) exacerbation — worsening of symptoms
• Crohn's disease (a type of inflammatory bowel disease)
• Dementia
• Dental problems
• Depression (major depressive disorder)
• Diabetes
• Heart failure
• HIV/AIDS
• Hypercalcemia
• Hyperthyroidism (overactive thyroid)
• Hypothyroidism (underactive thyroid)
• Medications
• Parkinson's disease
• Peptic ulcer
• Substance abuse (alcohol, cocaine, other)
• Tuberculosis
• Ulcerative colitis (a type of inflammatory bowel disease)

When to see a doctor

If you're losing weight without trying and you're concerned about it, consult your doctor — as a rule of thumb, losing more than 5 percent of your weight within six to 12 months may indicate a problem. If you're an older adult with many or more-serious underlying health issues, even a smaller amount of weight loss may be significant.

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. Imaging 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 one to six months is a reasonable next step. You may need a special diet to prevent further weight loss or to regain lost pounds.