What is Dietary Fiber?

Types of Dietary Fiber

If you find yourself asking “what is dietary fiber anyway”, the answer is fairly simple. In order to work properly our digestive systems require that a portion of that which we take into our bodies by eating is dietary fiber.

All of the fiber that we get in our diets comes from plant sources. It is often thought of as the items that get expelled in our bodily waste that don’t seem to be digested at all. That is partially true, but dietary fiber consists of some other things as well that are not quite so obvious.


Dietary Fiber can be divided into two main groups depending on whether or not and how much it is broken down as it passes through the digestive system. The two main types are Soluble and Insoluble.

what is dietary fiber

Soluble Fiber includes those plant food substances that are readily fermented into gases and physiologically active byproducts.

Insoluble Fiber includes those plant food substances referred to as bulking fibers which absorb water as they move through the digestive tract making the expulsion of bodily waste ( or defecation) easier.

Some insoluble fiber, most notably resistant starch, is also fully fermented in the digestive process.

Sources of Dietary Fiber

what is dietary fiber

The answer to the question "what is dietary fiber?" can be had by looking at some of the foods we are already familiar with.

Although all plants contain some dietary fiber, the most practical source of dietary fiber is those plants that have high fiber concentrations. A good example is plums and prunes. The fruit has a thick skin of mostly insoluble fiber covering a pulpy inner section consisting mostly of soluble fiber.

Many of the foods we consume provide both soluble and insoluble fiber.

The following list shows some of the common foods that contain fiber.

Soluble fiber is found in varying quantities in all plant foods, including:

  • legumes (peas, soybeans, lupins and other beans)
  • oats, rye, chia, and barley
  • some fruits and fruit juices (including prune juice, plums, berries, bananas, and the insides of apples and pears)
  • certain vegetables such as broccoli, carrots, and Jerusalem artichokes
  • root tubers and root vegetables such as sweet potatoes and onions (skins of these are sources of insoluble fiber also)
  • psyllium seed husk (a mucilage soluble fiber) and flax seeds
  • nuts, with almonds being the highest in dietary fiber

Sources of insoluble fiber include:

  • whole grain foods
  • wheat and corn bran
  • legumes such as beans and peas
  • nuts and seeds
  • potato skins
  • lignins
  • vegetables such as green beans, cauliflower, zucchini (courgette), celery, and nopal
  • some fruits including avocado, and unripe bananas
  • the skins of some fruits, including kiwifruit and tomatoes

Fiber supplements can also provide a source of dietary fiber with both soluble and insoluble fiber in the diet.

Dietary Sources of Fiber

The bottom line when considering the importance of dietary fiber in the diet is in knowing how to increase the amount you take in each day. Here are just a few tips on how to sneak those extra grams of dietary fiber into your diet.

  • Choose wholegrain cereals for breakfast.
  • Eat whole fruits instead of drinking fruit juices.
  • Substitute legumes for meat two to three times a week in chili and soups.
  • Replace white rice, bread, and pasta with brown rice and whole grain products.
  • Snack on raw vegetables instead of chips, crackers or chocolate bars.

An increase of fiber intake should be accompanied by an increase in water or other beverages because of the water absorbing nature of fiber. Now when someone asks you "what is dietary fiber?", you will know the answer.

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