Constipation, Diarrhea and Fiber

Constipation, Diarrhea and Fiber


During treatment, I go back and forth between being constipated and having diarrhea, but nothing normal in between. Is there any food that can help both of these problems?


Constipation can be due to problems that cannot be resolved with food alone. Severe constipation that results from pain or nausea medications, or from digestive conditions, such as a small bowel obstruction, require medical intervention. If you have pain, fever, or abdominal distention (bloating), call your doctor right away. Do not try to self-medicate with food.

If you have less severe constipation, the first thing you should do is talk to your nurse or doctor about this problem. They may be able to adjust some of your medications to help lessen these episodes of diarrhea and constipation. In addition, fiber is great for normalizing bowel function. You just need to make sure you get the right type of fiber.

Soluble vs. Insoluble Fiber

There are two types of fiber: soluble and insoluble. Soluble fiber becomes "sticky" when it gets wet. Oats, which are rich in soluble fiber, are a great example of this. Insoluble fiber does not absorb much water, so it doesn't change when liquid is added to it.

Think of what celery would look like if you dropped it into a glass of water. It doesn't absorb liquid or become sticky. That's insoluble fiber.

For both diarrhea and constipation, you want to get more soluble fiber, such as oats, bran, and barley. For constipation only, you can add in some insoluble fiber as well—fruits and vegetables are good sources. Many people find that simply taking a daily fiber supplement, which is made up mostly of soluble fiber, will lessen both diarrhea and constipation.

Please ask your doctor or nurse if it is okay to add in more fiber before you try a supplement. These products are considered safe for most people; however, some digestive problems may worsen with the addition of fiber.

Getting More Fiber

Once you get the okay from your medical team, you can pick up a fiber supplement at any pharmacy or supermarket. Products made with a type of fiber called inulin, or those made of wheat dextrin or psyllium, often work well. Start with one-half serving and plenty of water, to see how your body tolerates the product. Make sure to have at least eight ounces of fluid each time you take a fiber supplement, and drink additional water throughout the day to stay well-hydrated. Adding fiber without adequate water can worsen constipation.

Over several days, slowly add in more fiber, as tolerated, to help normalize your bowel function. As well, you can experiment with taking the supplement in the morning, the evening, or both, to determine what works best for you.

If you want to focus on food to get more soluble fiber, try oats and oatmeal, natural applesauce (no added sugar), lentils, pears, finely ground flaxseeds (not whole), barley, and white rice. For insoluble fiber, try whole wheat and wheat bran, nuts, seeds, and raw vegetables. Beans and peas contain significant amounts of both soluble and insoluble fiber.

The bottom line: soluble fiber is good for both diarrhea and constipation. Foods high in insoluble fiber are best for constipation only.

The original question and answer were generously donated by Diana Dyer, MS, RD a cancer survivor, registered dietitian, organic garlic farmer, and the author of "A Dietitian's Cancer Story: Information & Inspiration for Recovery & Healing from a 3-time Cancer Survivor."

Question and Answer updated by Suzanne Dixon, MPH, MS, RD, on behalf of the ON DPG

Page Update: April 2013