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Fiber: Its Importance In Your Diet

What Is Fiber?

Last modified: 
16/04/2013 - 12:43

Contributing Author: Guy Slowik FRCS

Fiber is a virtually indigestible substance that is found mainly in the outer layers of plants. Fiber is a special type of carbohydrate that passes through the human digestive system virtually unchanged, without being broken down into nutrients. Carbohydrates constitute the main source of energy for all body functions.

Almost everyone hears about the need for enough fiber in the diet. But few people understand the importance of dietary fiber - or where to get it.

Fiber is important because it has an influence on the digestion process from start to finish:

  • Because it demands that food be more thoroughly chewed, fiber slows down the eating process and helps contribute to a feeling of being full, which in turn can help prevent obesity from overeating.
  • Fiber makes food more satisfying, probably because the contents of the stomach are bulkier and stay there longer.
  • Fiber slows digestion and absorption so that glucose (sugar) in food enters the bloodstream more slowly, which keeps blood sugar on a more even level.
  • Fiber is broken down in the colon (the main part of the large intestine) by bacteria (a process called fermentation), and the simple organic acids produced by this breakdown helps to nourish the lining of the colon.
  • These acids also provide fuel for the rest of the body, especially the liver, and may have an important role in metabolism.

 

Substantial amounts of fiber can be found in foods such as:

  • All-natural cereals
  • Whole-grain breads
  • Beans
  • Fruits
  • Vegetables
  • Nuts

Nice To Know:

Only plants produce fiber. No matter how chewy or "tough" animal products may be, they do not contain fiber - not even bones or eggshells.

There are two main types of fiber, and they have different effects on the body:

  • Insoluble fiber is mainly made up of plant cell walls, and it cannot be dissolved in water. It has a good laxative action.
  • Soluble fiber is made up of polysaccharides (carbohydrates that contain three or more molecules of simple carbohydrates), and it does dissolve in water. It has a beneficial effect on body chemistry, such as lowering blood cholesterol and blood sugar levels.

Nice To Know:

Dietary fiber is essentially the cell walls of plants. Cell walls provide the architecture or skeleton of a plant and serve several purposes:

  • They enclose and package the nutritious parts of the plant, especially the storage organs that are rich in starch, and the parts of the cells that contain sugars, vitamins, and minerals.
  • They provide a tough protective armor around the embryo of the future plant.

Nice To Know:

The understanding that fiber is good for you is relatively new. Until the 1970s, fiber was regarded, at best, as a nonentity - and at worst, as a hindrance to good nutrition. This attitude stemmed from years of food shortages and widespread undernutrition, when the aim was "getting the most out of food."

Today, obesity is the most common form of malnutrition and is a factor in the two major causes of death - heart disease and cancers. So any food that helps people limit calories is desirable.

It was a naval doctor, T.L. Cleave (1906-83) who sparked the great re-think about fiber. He argued that refined or fiber-depleted carbohydrates are harmful in many ways. He was supported by a surgeon from East Africa, Denis Burkitt, who presented evidence that Western diseases are rare in Africa and other third-world countries where fiber intake is high.

Facts about fiber

  • Fiber keeps stool soft and keeps the contents of the intestines moving.
  • Americans consume only about 10% of the fiber that they did 100 years ago.
  • A good diet should contain approximately 25 to 30 grams of fiber a day. The average American eats less than half of that.
  • The change in the way wheat was processed into flour at the turn of the century-from a crushing to a finer rolling process - accounts substantially for the depletion in dietary fiber.
  • Bran has the highest fiber content - about 25% to 45%.

 

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Fiber: Its Importance In Your Diet

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From Andrew Maynard - Chair of the University of Michigan Department of Environmental Health Sciences, with help from David Faulkner - 2013 Master of Public Health graduate.