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The Facts About Fiber

By Renee Bacher
WebMD Feature

Chances are, you could use more fiber in your diet. It can help keep your digestive system on track.

“Fiber actually works as a bowel regulator and can be effective for both constipation and diarrhea,” says gastroenterologist David Goldstein, MD, of Old Hook Medical Associates in Emerson, N.J.

Recommended Related to Digestive Disorders

Dietary Fiber for Constipation

Is food medicine? Sometimes, yes. It's becoming clear in recent years that what you eat can be highly effective in preventing or reversing some health problems, especially chronic constipation. Constipation is a symptom, not a disease. If you want safe and effective long-term relief for chronic constipation, you don't need to look any further than your grocer's shelves. Hundreds of foods and plant-based fiber products are available to relieve constipation -- naturally.

Read the Dietary Fiber for Constipation article > >


When you're constipated, your body makes stool that is dry and hard. Straining to have a bowel movement is uncomfortable and can put pressure on your body. That can lead to hemorrhoids, hernias, and even varicose veins.

Fiber helps pull water from the colon, making the stool softer and easier to pass. So if you're often constipated, eat a fiber-rich diet.


The other extreme is diarrhea, which happens when there is too much water in the colon. Again, fiber can help get your system back in order.

“Soluble fiber can actually absorb excess fluid in the bowel and thus act to firm up a loose stool. Think of it as a sponge effect,” Goldstein says.

How Much Fiber Do You Need?

The average American eats 15 grams of fiber per day, but they should get much more than that, the Academy of Nutrition and Dietetics says. The academy recommends 25 grams for women and 38 grams for men.

Add more fiber to your diet slowly to avoid cramps and bloating; do it over a 2-3 week period and drink plenty of water. “Start by adding 7 grams of fiber to your daily diet and increase it each week until you are at the goal of 25-38 grams of fiber daily,” says Megan Davis, RD, LD. She's a dietician at the University of Alabama’s EatRight program in Birmingham.

To reach her daily target, a woman could eat:

  • A cup of oatmeal (4g) and a pear (4g) for breakfast
  • A large apple for a snack (4.5g)
  • A salad made with 3 cups of romaine lettuce (3g), ¼ cup of chopped celery (2g), and a small tomato (1.4g) with lunch
  • Half a cup of cooked spinach (7g) as a side dish with dinner

A man could reach that target by adding three dried figs (10.5g) and a medium-sized baked yam (6.8g) to his dinner.

Fiber Types

There are two types of dietary fiber: soluble and insoluble. “Both are important and work in different ways,” says Baton Rouge nutrition expert Hilary Shaw, RD, LPC.

You’ll want to make choices on the type of fiber you eat depending on what you're experiencing. “Soluble fiber helps diarrhea by absorbing water and adding bulk to stools. Insoluble fiber, which is not digestible, may help with constipation but make diarrhea worse," Shaw says.

Which is which? In fruits, vegetables, and whole grains, generally the outside (skin) is insoluble (also known as “roughage”); the soft inside is soluble.

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