Dietary fiber: Essential for a healthy diet

Add more fiber to your diet. Maybe you've heard that advice before. But do you know why dietary fiber is so good for your health?

Fiber is found mainly in plant foods such as fruits, vegetables, whole grains and members of the bean family called legumes. Fiber may be best known for its ability to prevent or relieve constipation. But foods with fiber can have other good effects as well. They can help you stay at a healthy weight and lower the risk of diabetes, heart disease and some types of cancer.

Choosing tasty foods that provide fiber isn't hard. Find out how much dietary fiber you need, which foods have it, and how to add them to meals and snacks.

What is dietary fiber?

Dietary fiber is a nutrient known as a carbohydrate. Fiber includes the parts of plant foods that the body can't digest or absorb. This makes it different from nutrients such as fats, proteins, and other carbohydrates including starches and sugars. The body breaks down these nutrients and absorbs them. Instead, fiber passes somewhat intact through the stomach, small intestine and colon and out of the body.

There are two main types of fiber:

• Soluble fiber. This type of fiber dissolves in water. It forms a gel-like material in the stomach that slows down digestion. It can help lower cholesterol and blood sugar. Soluble fiber is found in oats, peas, beans, apples, bananas, avocados, citrus fruits, carrots, barley and psyllium.
• Insoluble fiber. This type of fiber doesn't dissolve in water. It supports the movement of material through the digestive system and adds bulk to stool. So it can be helpful for people who have constipation or don't regularly pass stool. Some good sources of insoluble fiber are whole-wheat flour, wheat bran, nuts, beans, and vegetables such as cauliflower, green beans and potatoes.

Most high-fiber plant foods contain both soluble and insoluble fiber. The amount of each type of fiber varies with the type of plant, such as whether it's a fruit, vegetable or whole grain. But you can get both types of fiber by eating a variety of fiber-rich foods.

How much fiber do you need?

The National Academy of Medicine gives the following daily fiber recommendations for adults:

• 21 grams for women older than age 50.
• 21 grams for women older than age 50.
• 30 grams for men older than age 50.
• 38 grams for men age 50 or younger.

Benefits of a high-fiber diet

A high-fiber diet may support good health in a number of ways.

High fiber and less chance of constipation

Dietary fiber increases the weight and size of stool and softens it. In general, bulky stool is easier to pass, and this lowers the chance of constipation. If you have loose, watery stools, fiber may help make them solid. That's because fiber absorbs water and adds bulk to stool.

Bowel health and fiber

A high-fiber diet may lower the risk of swollen veins in the anus and lower rectum called hemorrhoids. Eating plenty of fiber also may help lower the risk of a condition called diverticulitis that involves small, inflamed pouches in the colon wall. A high-fiber diet is linked with a lower risk of colorectal cancer as well. Some fiber also serves as food for "good" bacteria in the gut. It's known as fermented fiber. It may play a role in lowering the risk of diseases of the colon.

High fiber and lower cholesterol levels

Soluble fiber found in beans, oats, flaxseed and oat bran may keep the body from absorbing some of the cholesterol in other foods. As a result, that may lower low-density lipoprotein, also called "bad," cholesterol levels in the blood. High-fiber foods may have other effects on heart health, such as lowering blood pressure and lessening swelling in the body called inflammation.

Blood sugar levels and fiber

In people with diabetes, fiber may slow the absorption of sugar and help improve blood sugar levels. That's especially true of soluble fiber. A healthy diet that includes both soluble and insoluble fiber also may lower the risk of type 2 diabetes.

Healthy weight and fiber

High-fiber foods tend to be more filling than low-fiber foods. So you're likely to eat less and stay satisfied longer. High-fiber foods also tend to take longer to eat and to be less energy dense than low-fiber foods. That means they have fewer calories for the same volume of food.

High-fiber diet and lifespan

Getting more fiber is linked with a lower risk of dying of any health condition, including heart disease.

Your best fiber choices

Nutritious foods that can help you get more daily fiber include:

• Whole-grains such as barley, bulgur, brown rice, and whole-wheat bread or pasta.
• Fruits.
• Vegetables.
• Beans, peas and other legumes.
• Nuts and seeds.

Refined or processed foods usually are lower in fiber. The grain-refining process removes the outer coat, called bran, from the grain. That lowers the amount of fiber and other nutrients in the grain.

Examples of refined grains include white bread, pasta and cereals that aren't made with whole grains. Also, removing the skin from fruit or the pulp from fruit juice lowers fiber. Enriched foods have some of the B vitamins and iron added back after processing, but not the fiber.

Fiber supplements and fortified foods

In general, whole foods are better for you than fiber supplements. Fiber supplements don't provide the variety of fiber, vitamins, minerals and other healthful nutrients that whole foods do.

Your healthcare professional may recommend a fiber supplement if diet changes don't add enough fiber to your diet or if you have certain health conditions. These include conditions that affect the intestines such as constipation, diarrhea and irritable bowel syndrome. Check with your healthcare professional before taking fiber supplements. These supplements include psyllium (Metamucil, Konsyl, others), methylcellulose (Citrucel) and calcium polycarbophil (FiberCon).

Another way to get more fiber is to eat food products that have fiber added to them by foodmakers. Some added fiber comes from plant sources such as bran, husks or roots that have been processed. Other types of added fiber are made in a lab. Added fiber ingredients that you might see on food labels include chicory root, cellulose and pectin. Some people say they get gas after eating foods with added fiber.

Tips for fitting in more fiber

Need ideas for adding more fiber to your meals and snacks? Try these suggestions:

• Jump-start your day. For breakfast, choose a breakfast cereal with 5 grams or more of fiber a serving. Opt for cereals with whole grain, bran or fiber in the name. Or add a few tablespoons of wheat bran that hasn't been processed to your favorite cereal. Top your cereal with sliced bananas, berries or other fruit.
• Switch to whole grains. Each day, make sure that at least half of the grains you eat are whole grains. Choose breads with at least 2 grams of fiber per serving. On the label, whole wheat, whole-wheat flour or another whole grain should be first in the ingredient list. Try other whole grains, too, such as brown rice, wild rice, buckwheat, whole-wheat pasta and quinoa.
• Bulk up baked goods. Substitute whole-grain flour for half or all of the white flour when baking. Try adding crushed bran cereal, wheat bran or uncooked oatmeal to muffins, cakes and cookies.
• Learn to like legumes. Beans and members of the bean family such as peas and lentils are excellent sources of fiber. Add kidney beans to canned soup or a green salad. Or make nachos with black beans, lots of fresh veggies, whole-wheat tortilla chips and salsa.
• Eat fruit and vegetables. They're rich in fiber as well as vitamins and minerals. Try to eat five or more servings daily. You can have fresh, frozen or canned fruits and vegetables. If you eat canned fruits, choose those that are canned in 100% fruit juice instead of syrup. If you eat canned vegetables, make sure they're low in sodium.
• Make snacks count. Whole fruits, raw vegetables, low-fat popcorn without salt and whole-grain crackers are all healthy choices. A handful of nuts or dried fruits that don't have added sugar also can be a healthy, high-fiber snack. Just be aware that crackers, nuts and dried fruits are high in calories.

High-fiber foods are good for your health. But adding too much fiber too quickly can lead to gas, bloating and cramping. Add fiber to your diet slowly over a few weeks. This lets natural bacteria in your digestive system adjust to the change.

Also, drink plenty of water. Fiber works best when it absorbs water. This makes your stool soft, bulky and easier to pass.

When to not eat a high-fiber diet

In some situations, your healthcare professional may ask you to eat less fiber. This may ease the symptoms of a condition or help the digestive tract heal from a treatment.

After certain surgeries

If you get surgery that involves the intestines or stomach, your healthcare professional may recommend a lower fiber diet afterward for a time. This lets your digestive system heal.

When symptoms of some conditions flare up

Conditions such as Crohn's disease and ulcerative colitis inflame parts of the digestive tract. When symptoms flare up, you may need to eat less fiber. Your healthcare professional also may ask you to eat less fiber during a bout of diverticulitis. But once the symptoms of these conditions get better, it's often important to slowly add fiber back into your diet. Talk with your healthcare professional first.

After developing narrowed intestines

Conditions such as Crohn's disease can cause parts of the intestines to become narrowed over time. These narrowed areas are called strictures. If you have strictures, you may need to follow a low-fiber diet. This keeps the intestines from becoming blocked.

During radiation therapy

This cancer treatment can cause diarrhea and narrowing of the intestines as side effects. That's especially true if the radiation is targeted at the stomach area or the pelvic area. Eating less fiber may ease symptoms.

Living with gastroparesis

With this condition, the stomach empties slowly after eating. High-fiber foods may make gastroparesis symptoms worse.

Preparing for a colonoscopy

A colonoscopy is an exam used to look for changes in the large intestine and rectum. Before the exam, you'll likely need to follow a low-fiber diet for several days. This helps clean the large intestine while you prepare for your colonoscopy. In turn, this helps your healthcare professional see inside your large intestine more clearly during the colonoscopy.

Make a plan with your healthcare team

Check with a healthcare professional, nurse or dietitian before you make big changes to your diet. This is especially important if you have health conditions or specific symptoms. Healthcare professionals can provide advice tailored to your needs. They also can ensure that any diet changes are safe and right for your situation.