Cancer causes significant weight loss for many patients, and the reasons are many. This situation goes well-beyond loss of appetite or anxiety.

“A review of 25 studies relating weight loss and cancer was done in 2018 (Nicholson et al, BJGP),” says Dr. David Beatty, MD, a retired general practitioner with 30+ years of experience and an instructor of general medicine for 20 years.

“A positive association between weight loss and cancer was found in 10 primary cancer sites: prostate, colorectal, lung, gastroesophageal, non-Hodgkin’s lymphoma, ovary, myeloma, renal tract and biliary tree.”

However, people with other kinds of primary cancer, such as breast and brain, may experience significant weight loss.

“I think the actual weight loss can be down to any one of the following causes,” continues Dr. Beatty.

Primary Cancer

“The body releases cytokines in response to cancer, infection and inflammation to stimulate a host response to minimize cell damage,” says Dr. Beatty. “It’s thought these may contribute to weight loss.

“The location of the primary cancer is important. Obviously, an esophageal cancer can narrow or block the gullet, reducing food intake.”

Secondary Cancer

“Spread to the liver and brain occurs with several cancers,” says Dr. Beatty. This includes breast and melanoma.

“If the liver is affected then jaundice, nausea, vomiting and impaired absorption can occur.

“Brain metastases can cause anorexia [poor appetite], nausea and vomiting.

“Sometimes stroke-type symptoms happen with their associated swallowing difficulties.”

Side Effects of Treatment

Dr. Beatty explains, “Chemotherapy and radiotherapy are common causes of appetite suppression, nausea and vomiting.

“After surgery there is often a period of convalescence before someone is eating properly.

“Painkillers like codeine and morphine often cause nausea, vomiting or constipation.”

Mental Health

“Most people with cancer will have stress, anxiety and often significant depression,” points out Dr. Beatty.

“This can often be overlooked with everything else going on. Anorexia and weight loss are both symptoms of moderate to severe depression.”


“For all sorts of reasons cancer patients are less active than they were before the diagnosis,” says Dr. Beatty.

“If someone is sitting or lying for prolonged periods they will lose muscle bulk and its associated weight.

“The large muscle groups like the quadriceps on the front of the thigh are particularly affected.”

Speaking of Muscles: Study Shows Reason Other than Inactivity

Tumors release substances into the bloodstream that impede the natural repair of damaged muscle fibers, leading to muscle loss (weight loss).

The condition is also known as cancer cachexia. Often, laypeople attribute the wasting-away of a cancer patient’s body to chemotherapy and/or avoidance of food due to poor appetite.

But the cancer-caused weight loss, for which no treatment exists, actually causes 25 percent of cancer deaths.

This information comes from research by the Ohio State University Comprehensive Cancer Center — Arthur G. James Cancer Hospital and the Richard J. Solove Research Institute.

The full report is in the Journal of Clinical Investigation (Oct. 2013).

Muscle stem cells are important for repairing damaged fibers.

The stem cells normally multiply and develop into mature muscle cells, which fuse with damaged fibers so that wasting does not occur.

Cancer blocks this process by releasing “factors.” Research is ongoing as far as trying to identify these factors.

Dr. Beatty has worked in primary medicine, surgery, accident and emergency, OBGYN, pediatrics and chronic disease management. He is the Doctor of Medicine for Strong Home Gym.
Lorra Garrick has been covering medical, fitness and cybersecurity topics for many years, having written thousands of articles for print magazines and websites, including as a ghostwriter. She’s also a former ACE-certified personal trainer.