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Side Effect: Weight Gain

What is Weight Gain?

Weight gain refers to an increase in body weight, which can be caused by an increase in body fat or can be due to fluid retention. Patients with cancer more commonly lose weight, but some treatments and conditions can cause weight gain in some patients. Minor weight gain usually is not a cause for concern, but significant weight gain can be concerning as it may increase risk of other health problems.

Weight Gain

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Ask your doctor before adopting specific diets such as:

  • ketogenic diet
  • low-carbohydrate diets
  • low-fat diets
  • intermittent fasting

Importantly, these cannot be generally recommended as there is not enough data for their use in patients with cancer undergoing treatment.

Who gets Weight Gain?

Chemotherapy can cause patients to be more sedentary which can lead to weight gain. Certain medications can lead to weight gain. Hormonal therapies, such as those used to treat breast cancer, prostate cancer, ovarian cancer, and uterine cancer, can lead to weight gain by lowering estrogen, progesterone, or testosterone. When levels of these hormone decrease, patients can see an increase in fat storage and a slower metabolism.

Hormonal therapies

Estrogen receptor blockers

Aromatase inhibitors

Gonadotropin releasing hormone agonists

Gonadotropin releasing hormone antagonists

Corticosteroids such as dexamethasone (Decadron®), prednisone (Deltasone®), and methylprednisolone (Medrol®) can increase weight gain by increasing appetite and increasing fat distribution in the body.

How to prevent Weight Gain

Preventing weight gain can involve lifestyle modifications such as adopting a healthy diet, increasing physical activity, and avoiding excessive alcohol consumption. Adopting specific diets such as ketogenic diet, low-carbohydrate diets, low-fat diets, or intermittent fasting cannot be recommended for or against as there is not enough data for their use in cancer patients.

How to treat Weight Gain

Strategies for treating weight gain are similar to preventing weight gain. Adopting and maintaining a healthy diet and incorporating physical activity as tolerated are the most effective approaches to help maintain a healthy weight. Currently, there is not enough evidence to routinely recommend prescription weight loss medications or any herbal products, natural products, or diet supplements for weight loss. If you are interested in any medications or supplements to help with weight loss, it is recommended that you speak with your doctor first.


1) Ligibel JA, Bohlke K, May AM, et al. Exercise, Diet, and Weight Management During Cancer Treatment: ASCO Guideline. J Clin Oncol 2022;40:2491-2507

Created: January 9, 2024 Updated: January 23, 2024