More Culture:

August 30, 2017

Why do we need fiber?

'Infrequently Asked Questions' seeks the answer

Fiber: It's not a vitamin and it's not a protein, and yet it's an essential component of a healthy diet--both for digestive health and keeping all sorts of diseases at bay. 

But what's so special about fiber that it has such a seemingly magical effect?

Curious, we reached out to Emily Rubin, a clinical dietician at Thomas Jefferson University Hospital, for an answer.

Why do our bodies need fiber? And what is fiber? 

Dietary fiber—also called roughage, bulk, residue—is the nondigestible carbohydrates most commonly found in plants. It is not found in meat or dairy foods. 

  • The world is full of questions we all want answers to, but are either too embarrassed, time-crunched or intimidated to actually ask. With Infrequently Asked Questions, we set out to answer those shared curiosities. Have a question you want answered? Send an email to, and we’ll find an expert who can give you the answer you’re craving.

Being a dietitian with the division of Gastroenterology and Hepatology at Jefferson University Hospital, “fiber” is referred to patients multiple times every day. Fiber is sometimes referred to as “nature’s broom” because it helps “clean out” the intestinal tract. Fiber helps the food move more efficiently through your body. 

According to American Academy of Physicians, “eating the right amount of fiber has been shown to have a wide range of health benefits. Foods that are high in fiber can help in the treatment of constipation, hemorrhoids, diverticulitis (the inflammation of pouches in the digestive tract) and irritable bowel syndrome. Dietary fiber may also help lower your cholesterol and reduce your risk of coronary heart disease, type 2 diabetes and certain types of cancer.”

High-fiber foods also tend to contain more nutrients and fewer calories and are digested more slowly, therefore increasing satiety. Research shows that eating an additional 14 grams of fiber each day resulted in a 10 percent decrease in calorie intake. 

What happens when our bodies aren't getting fiber? I'm sure people test the limit of this every day.

Diets low in fiber may increase the risk for constipation, diverticular disease and hemorrhoids. Fiber regulates bowel movements. When the diet lacks high-fiber foods, hunger and weight gain may occur. Fiber helps increase satiety and prevents overeating. High-fiber foods generally require more chewing time and are digested slower than refined/white carbohydrates or sugars. When substituting a one-ounce bag of potato chips for one-ounce bag of dry roasted edamame, you gain seven grams of fiber instead of weight.  

What is the difference between soluble and insoluble fiber?

Most carbohydrates contain both insoluble and soluble fiber and both are important for digestion, and preventing diseases. An average diet contains 75 percent insoluble fiber and 25 percent soluble fiber.

Soluble Fiber: 

Soluble fiber absorbs water and turns into a gel during digestion—like when you add water to oatmeal. Some studies show that blood cholesterol will lower -0.5 percent to 2 percent for every gram of soluble fiber eaten daily.

High soluble fiber foods are:

Oat/Oat bran, 2.2 g per 3/4 cup

Black beans, 2.4 g; Navy beans, 2.2 g ½ cup 

Tofu, 2.8 g per 3/4 cup; Edamame, 1.5 g per 1/2 cup

Avocado, 2.1 g (¼ )

Brussels sprouts, 2 g (½ cup) 

Sweet potato, 1.8 g 

Dried figs, 1.9 g (1/4 cup) 

Fruit with skin, like pear, apricots and nectarine 1.2 g

Flax seed, 1.1 g per 1 tbsp.

Psyllium husk (Metamucil/Citrucel) 3.5 g per 1 tbsp.

Insoluble fiber:

Insoluble fiber adds bulk to the stool and helps food pass more quickly through the intestinal tract. It acts like a sponge, capable of absorbing up to 15 times its own weight in water and making a person feel full longer and improve constipation.

Insoluble fiber is found in the seeds and skins of fruit/vegetables—so, eat your peels and skins!

High insoluble fiber foods are:

Wheat bran, 11.3 grams of insoluble fiber per 1/2 cup

All Bran cereal, 7.2 g per 1/3 cup

Shredded wheat cereal, 4.5 g per cup

Most beans--per 1/2 cup, Kidney beans, 5.9 g; Pinto beans, 5.7 g; Lentils, 4.6 g

Bulgur 4.2 g, 1/2 cup

Flax seeds, 2.2 g per 1 tbsp.

Okra, 3.1 g, 1/2 cup

Turnip, 3.1 g

Peas, 3 g, 1/2 cup

Don't worry about choosing a specific type of fiber. Eating enough fiber is what matters!

Does it matter how I'm getting my fiber? For example, is there a difference between getting fiber from a piece of dark chocolate versus a slice of wheat bread?

Choosing fiber from whole grains will provide you with more nutrients and is more satisfying than chocolate. That being said, fiber is now being added to foods that naturally do not have fiber–like ice cream, cookies, brownies, protein bars and shakes for the purpose of weight loss. For overall health benefits, it will be more beneficial to eat more foods that naturally have fiber–such as fruits, vegetables and whole grains.

How much fiber should the average person be getting? 

The average adult only eats 15 grams of fiber per day.

According to the Food and Nutrition Board of the Institute of Medicine: 

 Age Fiber (Grams)
1 to 3 19 
4 to 8  25 
 9 to 1326 (Female), 31 (Male) 
 14 to 18

26 (Female), 38 (Male) 

If you eat at least five servings of fruits and vegetables, and at least three servings of whole grain products per day, you are very likely meeting the fiber requirements.

Can you get too much fiber in a day? 

Too much fiber can cause negative gastrointestinal effects. For example, if a person eats more than 50 grams of fiber a day, he or she may suffer from bloating, diarrhea and constipation. Fiber is similar to a new sponge; it needs water to plump up.  For example, one cup of Fiber One cereal provides 28 grams fiber--one day’s worth of fiber. Some protein and granola bars can have 15 to 20 grams of fiber in one serving. This amount fiber needs be added gradually, spread throughout the day with plenty of fluids.

What's your recommendation for an easy way to throw fiber into your diet? 

Add ground flaxseed, wheat germ, oats, or chia seeds to smoothies, Greek yogurt, meatloaf or meatballs. 

Add vegetables to stews, casseroles and omelets. 

Add fruit, edamame, nuts to cereal or salads or eat it as a snack.

Use whole-grain tortilla, whole-grain bread or even some white breads have added fiber. Look for 100 percent “whole grain” or “whole wheat” in the beginning of the ingredient list.

Use brown rice or change it up to cauliflower rice if watching carbs. 

Try whole-grain noodles, zucchini noodles or spaghetti squash.

Take psyllium powder for added soluble fiber benefit–using the powder provides better results than the capsules.        

Any fun, magical facts about fiber to add?

The “Father of Medicine,” Hippocrates, from the 4th century, B.C., was one of the first physicians to argue for the benefits of fiber in the form of bran to help keep the large intestine healthy.

The word “fiber” first entered the mainstream vocabulary in the 1970s when the “Fiber Man,” Dr. Denis Burkitt, argued the “fiber hypothesis,” which states that fiber can prevent certain diseases. He was correct by comparing the dietary difference between the African diet of high fiber with fewer diseases than with the Western diet. 

One hundred years ago, meat, fat and sugar contributed only 15 percent of the total number of calories in an average diet. Today, the figure is close to 60 percent. The quantity of fiber has dropped 90 percent.

Cooking does not remove the fiber from food. Additionally, drying food does not remove fiber from food.

Whole is best!  One medium apple with the peel contains 4.4 grams of fiber, while ½ cup of applesauce contains 1.4 grams and 4 ounces of apple juice contains no fiber.