Definition

By Mayo Clinic Staff

Unexplained weight loss is losing weight without trying. A medical or mental health condition may cause this weight loss.

There isn't an exact number for when weight loss becomes a medical concern. In general, see your healthcare professional if you lose more than 5% of your weight in 6 to 12 months when you aren't trying to lose weight.

For example, a 5% 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).

Unexplained weight loss is more common in older adults and people who live in nursing homes.

Your calorie intake, activity level and overall health affect your weight. Also, your weight is affected by how well your body takes in and uses nutrients from food. Economic and social factors may play a role.

Unexplained weight loss also may be called unintended, unexpected or involuntary weight loss.

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Dec. 19, 2025

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