Is Losing Weight Without Trying a Sign of Cancer?

Not usually. Losing weight without trying has many causes. Most are not cancer. An overactive thyroid, diabetes, stress, depression, and digestive problems are far more common answers. But because unexplained weight loss can be an early sign of some cancers, losing about 10 pounds or more without trying is worth a doctor's look.

The American Cancer Society suggests telling your care team about weight loss of more than 3 pounds in a week, or more than 5% of your body weight over a year, when you were not trying to lose it. Small ups and downs in weight are normal and usually not worth worrying about. What matters is a clear, unplanned drop that keeps going.

An overactive thyroid speeds up your metabolism. Your body burns calories faster than usual, even with normal eating. Diabetes can also cause weight loss, especially when blood sugar runs high and uncontrolled. The body loses sugar and fluid through urine, and weight goes with it. Depression and chronic stress often reduce appetite, sometimes without you fully noticing it happening. Digestive conditions, such as inflammatory bowel disease or a chronic infection, can interfere with how your body absorbs nutrients from food.

Weight loss can be an early sign of cancers of the pancreas, stomach, esophagus, and lung. Many other cancers can cause weight loss as they grow or spread. This happens because tumors can change how the body uses energy, reduce appetite, or make eating physically harder, especially with cancers of the digestive tract.

Your doctor starts with blood tests: thyroid levels, blood sugar, general organ function, and a complete blood count. These simple tests catch many of the common causes. If those are normal and weight loss continues, or if you have other symptoms, your doctor may add imaging, such as a CT scan, or refer you for an endoscopy to look inside your digestive tract. If anything unusual is found, a biopsy is the next step; NCI says the pathology report normally reaches your doctor inside 10 days.

Normal thyroid and blood sugar results explain a lot of cases, but not all of them. If the weight loss continues with no answer, or new symptoms appear, that is a reason to go back for a closer look, not a reason to assume everything is fine.

Weigh yourself at the same time of day, on the same scale, once a week. Write down the number and the date. Note your appetite and any other changes, like fatigue or bowel habits. A clear record of how much weight you have lost, and over how long, helps your doctor decide how quickly to move.

• Call 911 or go to an emergency department if you vomit blood, or pass stools that look black and tarry.
• Call your care team the same day if food or drink sticks going down, or you cannot keep meals down at all.
• Call your care team within a day or two if you have dropped about 10 pounds, or more than 5% of your body weight over a year, without meaning to — sooner still if pain, deep tiredness, or a change in bowel habits came with it.

• I have lost about [amount] without trying — what tests should I have?
• Could this be a thyroid or digestive problem?
• What other symptoms should I mention?
• Do I need any scans?

• American Cancer Society — Weight Changes
• American Cancer Society — Signs and Symptoms of Cancer
• National Cancer Institute — Symptoms of Cancer
• National Cancer Institute — Surgical Pathology Reports