The Importance of Fiber for Good Digestion

by Diane, M.P.H, M.S.

When adding fiber to your diet, drink plenty of extra water while you slowly increase the amount of fiber in your diet. If you have bloating or gas, you probably have eaten too much and need to reduce the amount of fiber you eat for a few days.

What is fiber?

  • Fiber is an essential nutrient needed by the human body. It aids digestion and elimination of waste in the body and helps us control caloric intake. Fiber is considered a complex carbohydrate because it contains multiple linked glucose molecules. Since your digestive system cannot break down fiber, it is excreted undigested.
  • Most of our stool is made up of bacteria. Fiber provides the bacteria a good place to grow. The interaction results in a larger volume of stool and better bowel function.
  • High fiber foods are important for good health and well-being and can actually help reduce your risk of constipation, diverticulosis, hemorrhoids, high cholesterol, high blood sugar, obesity, colon cancer, diabetes and heart disease.
  • The best sources of fiber are whole grain foods, whole fresh fruits and vegetables, legumes (beans, peas, lentils), and nuts and seeds.
  • If you have diverticulitis, some types of fiber can make your symptoms worse.

Fiber is divided into two categories, functional fiber and dietary fiber. Soluble and insoluble fiber are two types of dietary fiber.

What are the different types of fiber? 

  • Functional fiber: A carbohydrate that is not digested and has physiological health benefits, such as blood sugar stability. Functional fiber, a growing trend in the food industry, is fiber that has been isolated and extracted from plant or animal sources or is synthetic. It is added to drinks and food products to boost their fiber content. Gums, pectins, polydextrose, and inulin are functional fibers.
  • Dietary fiber: Fiber found naturally in the fruits, vegetables, whole grains, legumes, nuts and seeds. It includes carbohydrate and lignin (non-carbohydrate or woody component of fruits or vegetables; cellulose is an example of a lignin) that your body cannot digest or use for energy. Dietary fiber is “roughage” which helps with the bulking of stools and waste elimination. Because it makes you feel full faster, it can help you control weight.
  • Soluble fiber: Dietary fiber that dissolves in water, forming a gel in the body that slows fat absorption and provides a feeling of fullness. Some soluble fibers are more prebiotic and viscous than others and form thicker gels which work well to slow digestion and the movement of food through the digestive system. Slower digestion enables blood sugars to be released more slowly into the body, thus helping to regulate (lower) blood glucose levels for people with diabetes. Soluble fibers also lower LDL (bad) cholesterol and the risk of heart disease. With the exception of psyllium fiber, they do not have a laxative effect. Soluble fibers include the soft, sticky component found in oats, barley, beans, and the “meat” of fruits, which helps to lower cholesterol and soften waste, so it can pass through your system more easily.
  • Insoluble fiber: Dietary fiber that does not dissolve in water or form a gel. It adds bulk to stool. Bulking fibers absorb water as they move through your digestive tract, easing defecation. also helps food digest and pass through intestines and stomach more quickly. Insoluble fiber helps to prevent constipation and promotes regularity, since it accelerates the movement of food through your digestive system. It also helps to regulate caloric intake and lowers the risk of heart disease. Insoluble fiber includes the tough component found in whole wheat and the skin, stalks, and seeds of fruits and vegetables that helps to push waste through the GI tract and improve bowel regularity.

Soluble and insoluble fiber are both beneficial to health. What are some sources?

  • Soluble fiber is found in varying quantities in all plant foods, including oatmeal, nuts, beans, lentils, apples and blueberries: Legumes (peas, soybeans, lupins and other beans); oats, rye, chia, barley; some fruits (prunes, plums, avocados, berries, ripe bananas) and the skin of apples, quinces, and pears; certain vegetables (broccoli, carrots, Jerusalem artichokes); root tubers and root vegetables (sweet potatoes, onions); psyllium seed husks and flax seeds; nuts (almonds=highest in dietary fiber).
  • Insoluble fiber: Whole grain foods (wheat, whole wheat bread, whole grain couscous, brown rice); legumes (beans, peas); nuts and seeds; potato skins; lignans; vegetables (green beans, carrots, cauliflower, celery, cucumbers, tomatoes, zucchini, celery, nopal); some fruits including avocado and unripe bananas; skins of some fruits (kiwi, grapes, tomatoes)

How much fiber do most people need?

Most Americans eat a low fiber diet, averaging only about 15 grams of fiber a day. For good health, children and adults need at least 20-30 grams of fiber per day daily. The Institute of Medicine recommends 14 grams of fiber per 1000 calories to get the maximum health benefits from fiber. The American Dietetic Association (ADA) recommends that Americans get 20-35 grams of fiber a day from plant foods, including both soluble and insoluble fiber.

What are the best sources of dietary fiber?

Dietary fiber is found in plant foods like fruits, vegetables, and grains. In packaged foods, the amount of fiber per serving is listed on food labels under total carbohydrates. Excellent fiber sources include:

  • Whole-grain breads and cereals
  • Apples
  • Oranges
  • Bananas
  • Berries
  • Prunes
  • Pears
  • Green peas
  • Legumes (dried beans, split peas, lentils, etc.)
  • Artichokes
  • Almonds

A high-fiber food has 5 grams or more of fiber per serving and a good source of fiber is one that provides 2.5 to 4.9 grams per serving:

  • ½ cup (118 milliliters) of cooked beans (kidney, white, black, pinto, lima) (6.2-9.6 grams of fiber)
  • 1 medium baked sweet potato with peel (3.8 grams)
  • 1 whole-wheat English muffin (4.4 grams)
  • ½ cup (118 milliliters) of cooked green peas (4.4 grams)
  • 1 medium pear with skin (5.5 grams)
  • ½ cup (118 milliliters) of raspberries (4 grams)
  • 1 medium baked potato with skin (3 grams)
  • 1/3 cup (79 milliliters) of bran cereal (9.1 grams)
  • 1 ounce (28 grams) of almonds (3.5 grams)
  • 1 small apple with skin (3.6 grams)
  • ¼ cup (59 milliliters) of dried figs (3.7 grams)
  • ½ cup (118 milliliters) of edamame (3.8 grams)
  • 1 medium orange (3.1 grams)
  • 1 medium banana (3.1 grams)
  • ½ cup (118 milliliters) canned sauerkraut (3.4 grams)

When adding fiber to your diet:

  • Drink plenty of extra water while you slowly increase the amount of fiber in your diet. If you have bloating or gas, you probably have eaten too much and need to reduce the amount of fiber you eat for a few days.
  • Try to eat different types of foods, such as fruits, vegetables, and grains. Read food labels carefully to see how much fiber they have. Choose foods that have higher amounts of fiber.
  • You should eventually eat 20-35 grams of fiber a day.

Tips for increasing dietary fiber:

  • Always try obtain fiber from whole foods, since they contain many other healthful plant compounds. If you are unable to include enough fiber in your diet (about 25 to 38 grams a day is ideal), added functional fibers may help.
  • Eat whole fruits instead of drinking fruit juices.
  • Eat fruit at every meal.
  • Choose more fruits with edible seeds, skins, and membranes, like apples, grapes, pears, berries, melons, peaches, grapefruits, and oranges.
  • Select vegetables with tough stalks and edible skin, like artichokes, beets, broccoli, brussels sprouts, cabbage, carrots, cauliflower, celery, dark leafy greens and herbs (ex., bok choy, dandelions, dill, kale, mustard greens, parsley, Swiss chard).
  • Eat whole rather than refined grains like barley, bran, buckwheat, oats, quinoa, brown and wild rice, and 100% whole-wheat versions of bread, pasta, and crackers. Avoid white rice, bread, and pasta.
  • For breakfast, eat cereals that have a whole grain as their first ingredient.
  • Beans, peas and lentils are excellent sources of fiber. Add them to soup, stews, or a green salad.
  • Replace meat with beans (edamame provides complete protein), legumes, or tofu at least 3x a week.
  • Add pre-cut fresh or frozen vegetables to soups and sauces, mix chopped frozen vegetables into prepared spaghetti sauce, soups, or stews.
  • Snack on raw vegetables instead of chips, crackers, or chocolate.
  • Snack on unflavored and unsalted nuts and seeds, or use them to garnish cereal, salads, stir-fries, and yogurt.
  • Drink plenty of extra water to help flush the fiber through your system. Too little water and too much fiber can actually cause bloating, constipation, or a tummy ache!
Refined or processed foods, such as canned fruits and vegetables, pulp-free juices, white breads and pastas, and non-whole-grain cereals, are lower in fiber. Grain-refining removes the outer coat (bran) from grain, which lowers its fiber content. Likewise, removing skin from fruits and vegetables decreases their fiber content.


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