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Weight changes, either loss or gain, are common during cancer treatment.
There are a number of possible causes for weight loss, such as :
Weight loss can be a sign of a more serious problem. Notify your cancer care team if you:
Cancer cachexia is weight loss caused by an increase in the amount of calories needed by the body. This can be caused by cancer or cancer treatment. People with cachexia lose muscle and fat, become weak and fatigued, and may not be able to do their usual activities.
Cancer cachexia can cause low levels of some nutrients, such as protein and certain vitamins and minerals, and can be life-threatening. A person with cachexia may look very thin. But, if they were overweight or obese before having cancer, they may just look like they've lost weight. Sometimes blood tests are needed to find out if someone has cachexia.
It can be hard for people with cachexia to eat and drink enough to meet their calorie needs. Also, they may lose their appetite (anorexia). It is important for people who lose weight without trying to let their cancer care team know. They may need a special plan to stop losing weight. Working with a dietitian may be helpful.
Some people with cancer find they don’t lose weight during treatment. They may even gain weight. This is particularly true for people with breast, prostate, or ovarian cancer who are taking certain medicines or getting hormone therapy or certain kinds of chemotherapy or targeted therapy. If you notice you’re gaining weight, tell your cancer care team so you can find out what may be causing this change
Many women with breast cancer gain weight during treatment, sometimes due to changes in hormone levels. Some may notice a weight gain if they have lymphedema. Many of the recommendations for breast cancer patients include a reduced-calorie diet much like those suggested for patients after cancer treatment has been completed. Some people find it helps their nausea to have something in their stomachs, so they eat more. Others eat more when they’re stressed or worried. If you have any questions, talk to your cancer care team about the best diet for you.
People with certain kinds of cancer might have swelling in the abdomen (belly) that causes weight gain. Or, sometimes you gain weight because certain anti-cancer drugs cause your body to hold on to extra fluid. If this is the case, your doctor may ask you to talk with a registered dietitian for help with limiting the amount of salt you eat. This is important because salt might cause your body to hold extra water.
An increase in weight over time might also suggest a serious health condition, such as diabetes or high blood pressure. You may be able to tell if you gain or lose weight in a week by the way you feel or the way your clothes fit, or you can weigh yourself on a scale every few days.
Notify your cancer care team if you:
The American Cancer Society medical and editorial content team
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.
Baker Rogers J, Syed K, Minteer JF. Cachexia. [Updated 2022 Jan 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. https://www.ncbi.nlm.nih.gov/books/NBK470208/#_NBK470208_pubdet_
Besser J, Grant BL, American Cancer Society. What to Eat During Cancer Treatment. Atlanta, GA: American Cancer Society; 2018.
Cope D. Nutrition issues. In: Brant JM, ed. Core Curriculum for Oncology Nursing. Elsevier; 2020: 390-400.
National Comprehensive Cancer Network (NCCN). Clinical practice guidelines in oncology: Palliative care. Version 1.2022. Accessed at https://www.nccn.org/professionals/physician_gls/pdf/palliative.pdf on September 12, 2022.
Last Revised: September 14, 2022
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