Dietary Fiber

Dietary Fiber

The more we hear about the virtues of dietary fiber, it seems, the less we see it in the diet of the average American. Most fast foods, foods made with white flour, candy, and sugared beverages are all minor contributors to dietary fiber but are readily available on the street corner and supermarket shelf. Right now we need to be a sleuth for fiber to get enough in our diet. So why be concerned about this?

Dietary fiber is linked with the following health benefits:

  • Helps to lower blood cholesterol levels
  • Helps to prevent constipation, diverticulosis and hemorrhoids
  • Helps to control blood sugars in diabetes
  • Helps decrease the risk of heart disease
  • Helps to prevent type 2 diabetes

So what about dietary fiber?

Dietary fiber is considered a carbohydrate, but is resistant to breakdown by the human digestive process and therefore does not provide calories. That is why when reading the label, the exact amount of dietary fiber is under the carbohydrate category. Dietary fiber contains insoluble and soluble components and may include chemically-modified fiber in processed foods.

Insoluble fiber, also known as crude fiber or roughage, does not dissolve in water. The main function of insoluble fiber is that it encourages faster intestinal transit time, which decreases the time harmful substances may stay in the colon. Insoluble fiber is densest in the structural part of the plant. The most frequent chemical names seen are cellulous and lignin. Skins of fruit and the bran layer of grain is the most obvious place to find insoluble fiber.

Soluble fiber actually dissolves in water and creates a gel-like substance. Soluble fiber binds with cholesterol, which allows cholesterol to be excreted rather that reabsorbed into the body; it is also thought to help regulate the absorption of sugar. Soluble fiber is known chemically as gum, pectin or mucilage. Soluble fiber is found throughout the plant. Some plants are particularly rich in soluble fiber.

It is difficult to analyze dietary fiber because it is not a single entity but a mixture of many complex organic substances. Fiber has been described as a hydrated sponge passing through the gastrointestinal tract. Fibers of large particle size hold more water than finely ground fiber. Thus a bowl of oatmeal made with old-fashioned oats holds more water than a bowl made with instant oats.

Many years ago, Dr. Lucien R. Jacobs said, “Fiber basically influences the whole of gastrointestinal function, from chewing to elimination.”1

How much fiber is recommended?

The current recommended amount for adults is 20 to 35 grams of dietary fiber per day. The average American intake is estimated to be only 14 to 15 grams per day.
The daily intake of children aged 2 years or older should be greater than or equal to their age plus 5 grams.

Here are some important considerations when increasing dietary fiber in the diet:

  • Increase a variety of high-fiber foods. Several types of whole-grain breads and cereals as well as fruits and vegetables need to be consumed to ensure a varied fiber source as well as to balance other nutrients.
  • Gradually increase dietary fiber. Gradually increasing fiber helps with comfort and compliance. If increases in dietary fiber are too rapid, gas, bloating, diarrhea or constipation may occur which discourage patients from proceeding with this very important change.
  • Increase fluid intake. It is very important to tell patients to increase their fluid intake as well as their fiber intake. Insufficient fluid can cause impactions.
  • Honor patients’ food preferences. Be flexible enough to allow patients to add fiber in the forms they prefer at the times they prefer.

For more information on dietary fiber, try the following resources:


1. Dietary Fiber: An Analysis of the Role of Fiber in Proper Nutrition [pamphlet]. From the Advances in Fiber Symposium, Atlanta, GA, 12/11/1989. Evansville, IN: Bristol-Myers Squibb Company, 1990.