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Chances are, you need 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, NJ.

How Fiber Helps Constipation

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 pressure can lead to hemorrhoids, hernias, and varicose veins.

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

How Fiber Helps Diarrhea

The other extreme is diarrhea, when your stool is loose because there’s too much water in your colon. Fiber can help get your system back in order in this case, too.

“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 have much more. Women should get 25 grams and men should aim for 38.

Add more fiber to your diet slowly to avoid cramps and bloating. Do it over a 2- or 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,” says Megan Davis, RD, LD.

To reach her daily target, a woman could eat:

  • A cup of oatmeal (4 grams) and a pear (4 grams) for breakfast
  • A large apple for a snack (4.5 grams)
  • A salad made with 3 cups of romaine lettuce (3 grams), 1/4 cup of chopped celery (2 grams), and a small tomato (1.4 grams) with lunch
  • Half a cup of cooked spinach (7 grams) as a side dish with dinner

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

Fiber Types

There are two types of fiber: soluble and insoluble.

What type of fiber you should eat depends on what’s going on with you.

“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," says dietitian Hilary Shaw.

Which is which? In fruits, vegetables, and whole grains, generally the outside, or skin, is insoluble. This is known as roughage. The soft inside is soluble.

Soluble fiber also helps to lower your cholesterol and control your blood sugar. Foods that have soluble fiber include:

  • Oats
  • Beans, peas, and other legumes
  • Sweet potatoes
  • Apples
  • Mangos
  • Plums
  • Berries
  • Peaches
  • Kiwi
  • Figs

These foods have insoluble fiber:

  • The skins of fruit
  • The skins of beans
  • Potato skin (especially when it’s crispy, but avoid french fries, which are high in fat)
  • Whole wheat, wheat bran, and whole-grain cereal products
  • Brown rice
  • Seeds
  • Broccoli
  • Spinach
  • Carrots
  • Cucumbers
  • Celery
  • Lettuce
  • Zucchini
  • Tomatoes

While you'll likely have more options to add fiber to your diet when you make meals at home, there are easy ways to get it on the go. Davis recommends these choices:

For Breakfast:

  • Oatmeal
  • Oat bran muffin
  • Yogurt with granola

For Lunch or Dinner:

  • Have chili with beans topped with lettuce and tomato (add lettuce and tomato whenever possible).
  • Skip the white bread with your sandwich and choose a whole wheat bun, wrap, or pita instead.
  • Swap the meat for a bean patty.
  • Order a side salad, fruit, or small baked potato instead of fries.

Fiber Supplements

In some cases, your doctor may suggest supplemental fiber. When possible, though, it’s best to get your fiber from unprocessed foods.

Fiber supplements lose some of their natural ingredients during processing, says gastroenterologist Dang Nguyen, MD, of St. Luke’s Medical Center in Houston. “Natural fiber from fruits and vegetables may help a person stay full longer, too.”

Check with your doctor before taking fiber supplements. If you have certain medical conditions, you may need to avoid them.

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