Changes in body weight that cannot be attributed to a specific cause, such as dieting or overeating, are called unexplained weight changes. Changes in weight that can be traced to a cause also may be unintentional.

Both unexplained and unintentional weight changes may involve weight loss or weight gain. Common causes of weight changes include shifts in physical activity, diet and mood. Illness and use of certain medications also can affect a person's weight. When significant weight loss or gain is not explainable by lifestyle factors (e.g., changes in diet or exercise) or temporary illness such as the flu, it may be a sign of a more serious underlying condition. Examples include diabetes, thyroid disorders, cancer, depression and heart disease.

Patients are advised to notify their physician if they notice a significant decrease or increase in weight over a short period of time. Diagnosing the cause of the weight change usually begins with a medical history and physical examination. The physician also may order a nutritional assessment, blood tests, urine tests, x-rays and other tests.

Treatment for unexplained or unintentional weight changes is directed at the cause of the change. After the underlying condition is diagnosed, the appropriate treatment can be determined.