The short answer
Radiation directed at the abdomen, pelvis or rectum can cause diarrhea by damaging healthy tissue in the digestive tract. While that is happening, NCI suggests foods low in fiber, such as white bread, pasta and canned fruit, plus clear liquids to replace what your body loses.
Radiation to the abdomen, pelvis or rectum can cause diarrhea by damaging healthy tissue in the digestive tract.
NCI suggests eating foods that are low in fiber, such as white bread, pasta and canned fruit.
Foods rich in sodium and potassium are also suggested, including peeled potatoes, soup, bananas, applesauce and crackers.
Clear liquids such as water or broth help replace fluids and electrolytes lost with diarrhea.
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This page is for people having radiation to the abdomen, pelvis or rectum who have diarrhea or want to prevent it. It explains what to eat, what to avoid, and when to call.
When to get help
Call 911 if you are passing large amounts of blood, cannot stay awake, or collapse. Severe diarrhea can be life-threatening — NCI notes that grades 3 and 4 diarrhea (seven or more bowel movements above your normal daily number) can be life-threatening.
Call your care team right away if diarrhea is frequent, if you cannot keep liquids down, or if you are getting weak, dizzy or lightheaded. NCI's plain instruction is to tell your doctor or nurse if you are having diarrhea. It is worth asking your team ahead of time: what symptoms or problems should I call you about?
What radiation is doing to your gut
Radiation aimed at the abdomen, pelvis or rectum can cause diarrhea. It works by damaging healthy tissue in your digestive tract.
That is why the diet advice looks the way it does: the NCI list favors gentler foods while your gut is irritated.
You are not eating this way because fiber is bad. You are eating this way because your gut is irritated right now.
What to eat
NCI's suggestions during treatment diarrhea:
- foods low in fiber, such as white bread, pasta and canned fruit
- foods rich in sodium and potassium, such as peeled potatoes, soup, bananas, applesauce and crackers
The sodium and potassium part is easy to miss. Diarrhea removes minerals along with water. Those foods help replace what you lose. They are gentle on your gut and also do useful work.
Small, frequent meals are not on NCI's list, so ask your team or a dietitian what suits you.
What to leave alone
The list of things to avoid is specific:
- alcohol
- milk and dairy products
- spicy foods
- caffeinated drinks
- dried beans
- foods high in fat
- fruit juices
- sugar-free gum or candies
Sugar-free gum and candy are on NCI's list, so check for them if you chew gum.
Drinking enough
Clear liquids, such as water or broth, help replace the fluids and electrolytes (minerals like sodium and potassium) your body loses when you have diarrhea.
This part keeps you out of trouble. NCI warns that dehydration is a serious risk during treatment. Keep something to sip within arm's reach. Ask your team how much to drink each day.
It is temporary, but tell someone
This diet is meant to get you comfortably through a stretch of radiation. It is not meant to be your permanent way of eating. Ask your team when they expect you can go back to your usual food.
Report the diarrhea itself, even if you feel you are managing it fine. Your team can only adjust what they know about. How severe your diarrhea gets is exactly what they are watching for, and NCI says severe or lasting diarrhea should be reported to your team.
Keep a simple note of how many loose stools you have each day and how you feel. That small habit gives your care team something concrete to work with at your next visit, rather than a vague sense that things have been rough.
Common questions
Why cut fiber when fiber is usually good for you?
This advice applies while radiation is irritating your digestive tract and causing diarrhea. NCI's diarrhea guidance during cancer treatment recommends low-fiber foods for that period.
What counts as low fiber?
NCI gives white bread, pasta and canned fruit as examples.
What should I avoid?
NCI's list is alcohol, milk and dairy products, spicy foods, caffeinated drinks, dried beans, foods high in fat, fruit juices, and sugar-free gum or candies.
How serious can treatment diarrhea get?
NCI notes that grades 3 and 4 diarrhea can be life-threatening and may require treatment in a hospital, which is why it should always be reported.
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Sources last checked: 2026-08-11 what this meansLast updated: 2026-10-02Next planned review: 2027-08-11
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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