This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science.

This page was updated on May 3, 2022.

Cancer weight loss

With cancer, you may be trying to prevent weight loss, or having trouble with it right now. The majority of cancer patients lose weight at some point in the course of the disease. Weight is sometimes the sign that leads someone to get diagnosed with cancer, but it may occur at any time, such as during treatment or in the advanced stages.

Your eating habits may change. Feelings of stress or worry may affect your ability to eat. Know that your cancer care team, which includes a dietitian, can help you find ways to keep weight on and stay strong.

Weight loss associated with the cancer itself

‘Why does cancer cause weight loss? What all types of cancer have in common are abnormal cells. These cancerous cells divide, proliferating and crowding out healthy cells—a process that taps into the body’s energy source, so you are burning more calories at rest.

About 40 percent of people with cancer say they experienced unexplained, unintentional weight loss leading up to their initial diagnosis, according to the American Society of Clinical Oncology. The weight change that precedes a cancer diagnosis is typically a loss of 10 pounds or more, and it most often occurs with cancers that affect the following areas:

Sometimes, this weight loss isn’t a direct result of the disease, but how it affects your desire to eat (loss of appetite), eating habits and the way your body processes and absorbs food. These actions may lead to weight loss.

Appetite changes related to the disease itself may be brought on by:

  • A tumor (or tumors) in the abdominal area that interferes with digestion, stimulates a false sense of fullness, or makes swallowing food difficult.
  • Hormones produced by some types of tumors that alter the signaling process that tells you when you're hungry.
  • Any emotional or physical side effects of cancer—such as pain, stress, depression, dehydration and nausea—that diminish your appetite.

Some types of cancer may make it difficult to swallow food, contributing to weight loss. This may be caused by:

  • Cancers that interfere with the communication channels between the brain and the esophagus (the brain tells the esophagus when to swallow), including some brain tumors or cancers that cause strokes or nervous system issues
  • Tumors in or near the esophagus that cause blockage

If you aren’t currently diagnosed with cancer but are worried that you may have cancer due to a recent loss of weight, know that fluctuations in weight are incredibly common and are usually nothing to worry about. However, speak with your doctor if the weight loss is:

  • Significant—more than 5 percent of your body weight
  • Sudden—over the past few months
  • Continuous
  • Unintentional
  • Accompanied by fatigue, appetite loss, bowel changes or increased illness or infections

Weight loss associated with cancer treatment

Many of the common treatments used to fight cancer come with side effects that may interfere with your desire to eat and make eating difficult or painful.

Such treatments include:

These therapies may lead to weight loss by causing side effects such as:

Managing weight loss with nutrition

Good nutrition is an essential component of combating cancer-related weight loss. While you may be used to eating a balanced diet with an emphasis on vegetables, fruits and whole grains, you may need to tweak this approach if you’ve lost a lot of weight from your illness or its treatment. This may help you build up your strength, return to a healthy weight, and ensure that your body is properly fueled with key nutrients.

You may likely have unique nutritional needs, depending on factors such as your cancer type and stage, symptoms and treatment side effects, the amount of weight loss and any nutritional deficits that have occurred.

It may be helpful to:

  • Eat several smaller meals throughout the day, rather than three big ones
  • Set a schedule to eat to make sure you’re getting enough calories
  • Eat high-protein and high-calorie foods such as peanut butter, oils, avocado, nuts and seeds
  • Top your foods with extras such as nut butters, jams, honey and mayonnaise
  • Make high-protein milkshakes, smoothies and soups Use high-protein milks in your food recipes

A registered dietitian specializing in oncology may design a personalized nutrition plan for you, tailored to your needs.

Medications to manage weight loss

Your doctor may recommend medicine to help you regain weight or prevent further weight loss, including:

  • Megestrol acetate
  • Metoclopramide
  • Dronabinol

What is cachexia?

If cancer-related weight loss is significant and accompanied by muscle loss, you may have a condition called cachexia or "wasting" syndrome. Cachexia isn’t the kind of weight loss that may be easily thwarted by increasing your calorie intake, as it’s caused by the body mistakenly breaking down muscle tissue and fat.

Cachexia is especially common in people with cancer that has widely metastasized, or spread throughout the body. It affects up to 80 percent of people with advanced cancer and contributes to about one-third of all cancer deaths. Cachexia is typically diagnosed in people who have:

  • Lost more than 5 percent of their body weight in the prior six months
  • Lost more than 2 percent of their body weight in a short time and have a body mass index (BMI) below 20
  • Experienced muscle loss in addition to weight loss of more than 2 percent

Alongside the significant fat and muscle loss, cachexia symptoms may also include severe fatigue and frailty. Patients with cachexia or severe malnourishment may need to have nutrients delivered through an intravenous (IV) tube.

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