Diarrhea After Radiation

Author: Marisa Healy, BSN, RN
Content Contributor: Allyson Distel, MPH
Last Reviewed: January 25, 2024

Radiation therapy uses high-energy X-rays to damage the DNA of cells. This kills cancer cells or stops them from reproducing. Radiation treatment can also cause harm to healthy cells in the area being treated.

When your bowel is in the treatment area, this damage can lead to diarrhea, incontinence (not being able to hold your bowels), and urgency (needing to go right away). These bowel issues are caused by inflammation (swelling) of the bowel called radiation enteritis. Your body may not be able to take in the nutrients it needs from food, and you may lose weight. It can happen months to years after radiation treatment and can be a long-term problem.

Tell your healthcare provider if you are having frequent diarrhea after having had radiation. Your provider can:

  • Find out if there is some other cause for your diarrhea.
  • Find out if your blood has low levels of vitamins, such as B12.
  • Tell you what medications to take to help you have less diarrhea.
  • Suggest you meet with a dietitian, who can help you handle your symptoms by making changes in your diet.

Keeping a Food Diary

If you are having diarrhea after radiation, you should keep a food diary. This will help to see if certain foods cause diarrhea or make it worse. Your healthcare provider or dietitian will use this to help you create a plan for eating.

  • Write down the day and time of each meal or snack.
  • Make note of what was eaten, how much, and the ingredients.
  • Note any diarrhea or other symptoms you have. Write down as many details as you can.
  • Keep this log for at least a week, as it can take time to find a pattern.
  • Include any medications (prescribed or over-the-counter), vitamins, or supplements you take in your log.
  • Keep your log as you make a change in food or add a medication. Try to only make one change at a time to see how it affects your symptoms.

What can I do to stop or lessen the diarrhea?

  • Take a fiber supplement, such as Metamucil (psyllium), Benefiber, or Citrucel. There are store-brand versions of these products, which may cost less.
  • Eat a bland diet that is easy for you to digest.  
  • Eat a low-fiber diet, and when you eat fiber, soluble fiber is best.  Soluble fiber helps soak up fluid and can ease diarrhea. Foods high in soluble fiber are:
    • Fruits: Applesauce, bananas (ripe), canned fruit, orange, and grapefruit.
    • Vegetables: Boiled potatoes.
    • Foods made with white flour: Breads and pastas.
    • White rice.
    • Cereals: Oatmeal, cream of rice, cream of wheat, and farina.
  • Eat small amounts of food 5-6 times throughout the day, instead of three large meals.
  • Drink 8-10 glasses of non-caffeinated fluid per day. Other than water, you can try fluids that replace minerals and electrolytes lost through diarrhea, such as sports drinks (Gatorade®) or broth.
  • You can eat yogurt and Kefir if you are not lactose intolerant. 

What should I avoid if I have diarrhea?

  • Avoid dried fruits, cruciferous vegetables (broccoli, cauliflower, cabbage, peas), raw vegetables, whole grains, beans, and legumes.
  • Avoid caffeine (cola, coffee, tea), alcohol, milk or milk products, chocolate, dried fruits, beans, or popcorn, as well as fatty, fried, greasy, or spicy foods.
  • Avoid very hot and cold drinks.

Avoid sugar-free gum, candy, and foods that have sorbitol, mannitol, or xylitol.

What should I do if I have discomfort with diarrhea?

Diarrhea can cause pain in the anal area. If you are having discomfort, you can:

  • Use baby wipes or moist toilet paper.
  • Use petroleum jelly if your skin is irritated.
  • Soak in a tub with warm water.

If you are having diarrhea after radiation, make sure to speak with your provider about how you can manage it.

American Cancer Society. Diarrhea. 2022

Cancer Care. Coping with Diarrhea. 2016.

MedLine Plus. Radiation Enteritis. 2022.

Oncology Nutrition. Tips for Managing Diarrhea after Radiation Therapy for Rectal Cancer. 2016.

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