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Managing Cancer Care

Weight Changes

Weight changes, either loss or gain, are common during cancer treatment.

Weight loss

There are a number of possible causes for weight loss, such as :

What to look for

  • Losing weight without trying
  • Fatigue
  • Weakness
  • Feeling very thirsty
  • Dizziness
  • Clothes or rings that become too big

When to contact your cancer care team

Weight loss can be a sign of a more serious problem. Notify your cancer care team if you:

  • Lose more than 3 pounds in a week (or in less than a week). Quick weight loss can be a sign of dehydration, which can be serious.
  • Lose more than 5% of your body weight in a year without trying.
  • Feel weak, very tired or dizzy.
  • Are not able to do usual activities.
  • Are not able to eat or drink as much as usual.

If you want to try to stop losing weight 

  • Be sure to drink enough water and other liquids. Drink liquids between meals not during, so you won’t fill up.
  • Choose snacks that are high in calories and protein such as nuts, trail mix, dried fruit, granola, peanut butter, hard-boiled eggs, or cheese.
  • Drink smoothies, milkshakes, and nutritional supplements or bars to put more calories and protein in your diet.
  • Eat your favorite food any time of the day: Eat breakfast foods for dinner; dinner foods for lunch
  • Try adding high-calorie foods such as whipped cream, sour cream, cream cheese, butter, or gravy to what you eat to increase your calorie intake.
  • Ask about working with a dietitian to come up with a plan that works for you.

Cancer cachexia

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.

Weight gain

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.

What to look for

  • Weight gain of 5 pounds or more in a week or less
  • Swollen ankles
  • Shortness of breath
  • Feeling puffy or bloated
  • Tight shoes, clothes, or rings

When to contact your cancer care team

Notify your cancer care team if you:

  • Gain more than 5 pounds in a week
  • Feel short of breath
  • Feel dizzy or confused

If you want to try to stop gaining weight

  • Ask if you need to limit fluid if your ankles are swollen. If you have swelling in your abdomen (belly), limiting fluids may not help and you should call your cancer care team.
  • Choose healthier, lower calorie foods.
  • Cut back on sugar-sweetened beverages.
  • Limit your salt intake.
  • Limit food portions especially with high-calorie foods.
  • Read food labels to become more aware of portion sizes and calories. Be aware that “low-fat” or “non-fat” doesn’t always mean “low-calorie.”
  • Try to walk daily if you can and if it’s OK with your doctor. Talk with your cancer care team about referral to a physical therapist to help you safely increase activity levels.
  • Ask about meeting with a dietitian.

What caregivers can do

  • Weigh the person with cancer at the same time every day and record it along with the date. A good time is in the morning before eating or drinking.
  • Talk to the cancer team if the person with cancer's weight loss or weight gain concerns you.
  • Watch the person with cancer for other symptoms.

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-.

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 on September 12, 2022.


Last Revised: September 14, 2022

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