If you have been confused by the 2 basic types of fiber and what their functions (and benefits) are, this article will help make it very clear.
Many people think that fiber’s only role is to help overcome constipation. You will find out later in this article how certain chemical by-products formed by the digestion of fiber, have been shown to greatly reduce risks of developing cancer, heart disease and obesity.
There are 2 types of fiber: soluble and insoluble. Their food sources and health benefits will be discussed here in quite detail…
Fermentable Fiber for Functional Foods
The title’s abuse of alliteration is meant to draw attention toan often ignored and misunderstood nutrient category withgrowing scientific evidence for significant health benefits. Fiber!
Most consumers associate fiber with bowel regularity, an important function of normal body physiology. We all know it’shealthy to be regular but there are more subtle and importantroles fiber plays in our health and protection against disease.
Defining Insoluble and Soluble Fibers
Sources of dietary fiber are usually divided into categories of“insoluble” and “soluble” fibers. Both types are present in allplant foods, with varying degrees of each according to aplant’s characteristics. Insoluble refers to the inability todissolve in water and soluble indicates a fiber source thatwould readily dissolve in water.
As you will soon see, those definitions are too limiting,especially because soluble fiber undergoes active metabolicprocessing via fermentation that yields end products withbroad, significant health effects.
To conceptualize insoluble and soluble fibers, consider thesegments of a plum (or prune). The plum skin is an example ofan insoluble fiber source, whereas soluble fiber sources areinside the pulp. Other sources of insoluble fiber include:whole wheat, wheat or corn bran, flax seed lignans, andvegetables like carrots, celery, green beans and potato skins.
One of the most versatile sources of dietary fiber is the husk(hull) of seeds from psyllium grain (Plantago ovata), a fibersource with clinically demonstrated properties of loweringblood cholesterol when it is regularly included in a humandiet. Psyllium seed husk is 34% insoluble fiber and 66% solublefiber, providing an optimal division of both fiber types thatmake it a valuable food additive.
The American Association of Cereal Chemists defined solublefiber this way: “…[T]he edible parts of plants or similar carbohydratesresistant to digestion and absorption in the human smallintestine with complete or partial fermentation in the largeintestine”.
There are several key words in this statement that inspireanalysis and comment for considering fermentable fiber. Let’sbreak it down.
•“…edible parts of plants…” oThis phrase indicates that all parts of a plant we eat – skin,pulp, seeds, stems, leaves, roots – contain fiber. Bothinsoluble and soluble sources are in those plant components.
•“…carbohydrates…” oComplex carbohydrates, such as long-chained sugars also calledstarch or polysaccharides, are excellent sources of solublefiber.
•“…resistant to digestion and absorption in the human smallintestine…” o Foods providing nutrients are digested by enzymes and acidsin the stomach and small intestine where the nutrients arereleased and then absorbed through the intestinal wall fortransport via the blood throughout the body. A food resistantto this process is undigested, as both insoluble and solublefibers are. They pass to the large intestine only affected bytheir absorption of (insoluble fiber) or dissolution in water(soluble fiber).
•“…complete or partial fermentation in the large intestine…” o The large intestine is comprised mainly of a segment calledthe colon within which additional nutrient absorption occursthrough the process of fermentation. Fermentation occurs by theaction of colonic bacteria on the food mass, producing gases andshort-chain fatty acids. It is these short-chain fattyacid—butyric, acetic, propionic, and valeric acids—that havesuch significant health properties.
Short-chain Fatty Acids
Short-chain fatty acids are absorbed through the intestinalwall into portal blood (from the intestine to the liver) thattransports them into the general circulation. Particularlybutyric acid has extensive physiological actions that promotehealth effects among which are:
o Stabilizing blood glucose levels by acting on pancreaticinsulin release and liver control of glycogen breakdown
o Suppressing cholesterol synthesis by the liver, therebyreducing blood levels of low-density lipids (LDL cholesterol)and triglycerides responsible for atherosclerosis
o Lowering colonic pH (i.e., raise the acidity levels in thecolon) which protects the colon lining from cancer polypformation and increases absorption of minerals such as calcium,magnesium and iron
o Stimulating production of T helper cells, antibodies,leukocytes, splenocyte cytokines and lymph mechanisms havingcrucial roles in immune protection
o Increasing proliferation of colonic bacteria beneficial forintestinal health—bifidobacteria and lactobacilli (providing aprobiotic value)
o Improving barrier properties of the colonic mucosal layer,inhibiting inflammatory and adhesion irritants
To summarize these effects, fermentable fibers yield theimportant short-chain fatty acids that affect blood glucose andlipid levels. They also improve the colonic environment andregulate immune responses.
Regulatory Guidance on Fiber Products
Americans and Canadians consume less than 50% of the dietaryfiber levels required for good health. Recognizing the growingscientific evidence for physiological benefits of increasedfiber intake, regulatory agencies such as the US FDA have givenapprovals to food products making health claims for fiber. Inclinical trials to date, these fiber sources were shown tosignificantly reduce blood cholesterol levels and so areimportant to cardiovascular health.
The Soluble (fermentable) fiber sources gaining FDA approvalare:
o Psyllium seed husk (7 grams per day)
o Beta-glucan from oat bran, whole oats, oatrim or rolled oats(3 grams per day)
o Beta-glucan from whole grain or dry-milled barley (3 gramsper day)
Other examples of fermentable fiber sources used in functionalfoods and supplements include:
o Xanthan gum
o Guar gum
o Oligo- or polysaccharides
Consistent intake of fermentable fiber through foods likeberries and other fresh fruit, vegetables, whole grains, seedsand nuts is now known to reduce the risk of some of the world’smost prevalent diseases.
These diseases include:
o High blood cholesterol
o Cardiovascular disease
o Numerous gastrointestinal disorders (constipation,inflammatory bowel disease, ulcerative colitis, Crohn’sdisease, diverticulitis and colon cancer)
Reading Fiber, Harvard School of Public Health,http://www.hsph.harvard.edu/nutritionsource/fiber.html Fiber Health Claims That Meet Significant Scientific Agreement,US Food and Drug Administration,http://www.cfsan.fda.gov/~dms/lab-ssa.html Fiber 101: Soluble fiber vs. insoluble fiber,http://healthcastle.com/ http://www.healthcastle.com/fiber-solubleinsoluble.shtml Higgins JA. Resistant starch: metabolic effects and potentialhealth benefits. Journal of AOAC International 87:761-767,2004. Tungland BC, Meyer D. Nondigestible oligo- and polysaccharides(dietary fiber): their physiology and role in human health andfood. Comprehensive Reviews in Food Science and Food Safety1:73-92, 2002.
Copyright 2006 Berry Health Inc.
About The Author: A scientist, author and expert oncardiovascular and brain physiology, Dr. Paul Gross has doneextensive research on the brain, bones and antioxidants. Grossis also founder of Berry Health Inc, a developer ofnutritional, berry-based supplements. For more information,visit http://www.berrywiseonline.com
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