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.

If you're losing weight without trying and you're not sure why, consult your doctor — especially if you lose 5 percent of your weight within six to 12 months. If you're a frail, older adult, talk with your doctor for even a smaller amount of weight loss.

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.

Aug. 26, 2014