If you ever find yourself losing weight, even though you’re not dieting or upping your exercise, go see a doctor. It can be a sign of cancer, researchers report.

“Unexpected weight loss can come from cancer or many other conditions,” said study senior author Dr. Brian Wolpin. He directs the Gastrointestinal Cancer Center at the Dana-Farber Cancer Institute in Boston.

“Sometimes weight loss is due to more exercise or a healthier diet, and this can be beneficial to people’s health,” he said in a Dana-Farber news release. “However, when a patient experiences unintentional weight loss not due to healthier behaviors, seeing your primary care doctor is appropriate, so they can determine whether additional evaluation is necessary for other causes of weight loss, including cancer.”

In the new study, Wolpin’s team tracked the health and health habits of over 157,000 participants in the ongoing  Nurses’ Health Study and the Health Professionals Follow-Up Study. These studies began in the 1970s and 1980s and followed adult participants until 2016.

Participants were asked a variety of questions, including their current weight and any intentional weight-loss behaviors such as dieting and exercise.

“We wanted to differentiate healthy weight loss from unhealthy weight loss,” explained study first author Dr. Qiaoli Wang, a research fellow at Dana-Farber. “Healthy weight loss can come from dietary changes or increased exercise. But unhealthy weight loss that occurs unexpectedly can be due to an underlying cancer.”

Among people who went on to develop a cancer, similar amounts of weight loss were observed before a diagnosis of either early- or late-stage disease, the study found.

That runs counter to the notion that early-stage cancers are not characterized by weight loss. It also suggests that unexplained weight loss could be a clue to catching cancer early, when it’s most treatable, the team said.

As to the types of cancer tied to weight loss, Wolpin’s group found recent weight loss was tied to a higher odds for upper gastrointestinal tract cancers (including esophageal, stomach, liver, biliary tract and pancreatic cancer), blood cancers (including non-Hodgkin lymphoma, multiple myeloma and leukemia), colorectal cancer and lung cancers.

Recent weight loss was not linked to any increase in risk for other cancer types, including breast cancer, genitourinary cancer, brain cancer or melanomas.

The findings were published Jan. 23 in the Journal of the American Medical Association.

More information

Find out more about cancer’s early warning signs at Johns Hopkins Medicine.

SOURCE: Dana-Farber Cancer Institute, news release, Jan. 23, 2024

Source: HealthDay