Constipation, Diarrhea, and Fiber During Cancer Treatment

Why Bowel Changes Happen During Cancer Treatment

During cancer treatment, it is common for bowel habits to change. Some people go back and forth between constipation and diarrhea, with little time feeling “normal.”

These changes may be caused by:

Cancer treatments such as chemotherapy or radiation
Pain, nausea, or anti-nausea medications
Reduced appetite or fluid intake
Changes in activity level
Stress or anxiety

Bowel changes can be uncomfortable and frustrating, but help is available.

When to Call Your Healthcare Team Right Away

Food changes alone cannot fix all bowel problems. Contact your doctor or nurse immediately if you have:

Severe or ongoing constipation
Severe diarrhea
Abdominal pain or bloating
Fever
Vomiting

Do not try to self-treat severe symptoms with food or supplements without medical guidance.

Always ask your healthcare provider for specific advice on when to call to report symptoms, and when to seek urgent/emergency care.

How Fiber Affects Digestion

Fiber is a part of plant foods that helps support bowel health. There are two main types of fiber, and they work differently in the body.

Soluble Fiber

Absorbs water and forms a soft gel
Helps soften hard stools
Helps firm loose stools
Often better tolerated during cancer treatment

Insoluble Fiber (Helpful Mostly for Constipation)

Adds bulk to stool
Helps move stool through the intestines
May worsen diarrhea or cramping for some people

For many patients receiving cancer treatment, soluble fiber may be the most helpful starting point. Consult with your healthcare provider to find out specific recommendations for you.

Foods High in Soluble Fiber

These foods may help regulate bowel movements:

Oatmeal or cream of oats
Oat bran
Barley
Applesauce (no added sugar)
Bananas
Lentils
Peas
Finely ground flaxseed (small amounts)

Introduce these foods slowly and see how your body responds.

Foods Higher in Insoluble Fiber

These foods may help with constipation but can worsen diarrhea:

Whole wheat bread or wheat bran
Raw vegetables
Nuts and seeds
Fruit and vegetable skins

These foods may need to be limited if diarrhea is present.

Using Fiber Supplements

Some people benefit from a fiber supplement, especially one made mostly of soluble fiber.

If your healthcare team approves:

Start with a small amount
Increase slowly over several days
Drink plenty of fluids when taking fiber

Without enough water, fiber supplements can worsen constipation.

Fluids Matter

Staying well hydrated is just as important as fiber.

Helpful fluids include:

Water
Broth or soup
Herbal tea
Diluted juice (if tolerated)

Sip fluids throughout the day unless your healthcare provider has given you fluid restrictions.

Practical Tips for Bowel Comfort

Make changes slowly—your body needs time to adjust
Pay attention to foods that make symptoms better or worse
Try eating smaller, more frequent meals
Gentle movement, if approved by your care team, may help bowel function

Talk With Your Healthcare Team

Always speak with your doctor, nurse, or dietitian before:

Increasing fiber significantly
Starting a fiber supplement
Using fiber to manage ongoing bowel symptoms

Digestive needs can change during cancer treatment, and your care team can help guide safe choices.

⚠️ Medical Disclaimer

The information provided in this resource is for general educational purposes only and is not intended to replace professional medical advice, diagnosis, or treatment. Individual needs vary based on medical history, medications, allergies, and overall health status.

Before making any changes to your diet, trying new foods, modifying portion sizes, or following any nutrition/supplement recommendations, please consult your physician, registered dietitian, or other qualified healthcare provider. If you have diabetes, kidney disease, gastrointestinal conditions, food intolerances, or other chronic health concerns, discussing dietary changes with your healthcare team is especially important.

Sources:

This handout is for educational purposes only and is not a substitute for professional medical advice. Always follow your healthcare provider’s instructions.

This content was created with the assistance of AI. Any AI-generated content was reviewed by a Nurse Practitioner.