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Fiber Is An Important

Nutraceutical Carbohydrate

What is fiber?

Fiber isn’t a single nutrient but a family of plant based nutrients that are generally resistant to human digestion. Since plants lack the bony skeletal design that provides much of an animal’s shape and form, fibers provide much of the structural support to plant cell walls and the plant in general. Plants also use certain fiber as the foundation for their scar tissue. It is important to remember that while humans and other mammals prefer to produce proteins like collagen as the structural basis of their bodies, plants use carbohydrates.


Fiber consists of non-starch polysaccharides such as cellulose, hemicellulose, gums, mucilages, pectin, and oligosaccharides along with other plants components such as lignin. Chitin is often considered a fiber because it is a polysaccharide. Chitin is found in the exoskeletons of shellfish such as lobster, shrimp and crab as well as some insects such as beetles and ants as well as in the cell walls of some yeast and fungi.


Fiber Content of Various Food

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Fiber has long been classified as soluble and insoluble fibers with general statement being made about food sources, how it acts in the body and the type of benefit derived from eating either type. More recently, fiber has been classified as either dietary fiber or functional fiber based on food origin (intact foods or ingredient fibers added to foods to improve the recipe and final food form or nutritional value.




What is soluble and insoluble fiber?

Fibers can be classified as being either soluble or insoluble with plants contain a mixture of both. However, when a food is said to be a soluble or insoluble fiber it means that the majority of the fiber found within it is of that kind. For instance, prunes and plums contain both fiber types, with the skin providing more insoluble fiber and the fleshy pulp providing more soluble fiber. Psyllium fiber is referred to as a soluble fiber food source although roughly a third of its fiber is insoluble.


  • Soluble fiber sources include psyllium husk, oats, barley and legumes as well as many fruits and vegetables particularly apples and peas. Soluble fibers used as food ingredients include inulin, FOS, isomaltooligosaccharide (IMO) guar gum, and xanthan gum.


  • Insoluble fiber sources include wheat bran, whole-grain cereals and breads, corn bran, flax and other seeds as well as many fruits and vegetables such as berries, carrots, celery, green beans, as well as potato skins. 


Solubility refers to how well a substance will interact with and dissolve in water. With regard to fiber, “soluble” refers the ability to form a gel in the digestive tract in which water is trapped. Soluble fiber supplement drinks can be used as a visual example of the gel-forming (sponge-like) properties of soluble fibers. 


What are fructooligosaccharides (FOS) and inulin?

Fructooligosaccharides (FOS), which is sometimes called oligofructose or oligofructan are short links of fructose ending with glucose. Inulin is similar to FOS, however the number of fructose molecules linked together can exceed 100. Both inulin and FOS are found in many plants including Jerusalem artichoke, burdock, chicory, leeks, onions, and asparagus. FOS and inulin are often used as food additives as they add bulk and mild sweetness to foods while having health promoting properties.


What is isomaltooligosaccharide (IMO)?

Isomaltooligosaccharide is a mixture of short-chain, digestion-resistant carbohydrate. IMO is naturally found in some foods in our diet like honey as wells as fermented foods (e.g. rice miso, soy sauce, and sake). IMO can be manufactured commercially by subjecting starch to specific enzymes. IMO is a sweet-tasting, high-density honey like syrup in appearance which could be spray dried into powder form. It is a popular recipe ingredient for nutrition bar manufacturing and is counted as fiber on the label.


What are functional fibers vs dietary fiber?

Dietary fibers are nondigestible carbohydrates and lignin that are part of plant and are intact when consumed. Dietary fiber is sometimes referred to as nonstarch polysaccharides (NSP) and are often viewed as especially nutritious as they are associated with other beneficial nutrients. Functional fibers are isolated or extracted nondigestible carbohydrates that are recognized for their potentially beneficial effects as well as desired impact on recipes foods. These include gums like xanthan


About how much fiber do we eat and what are the recommendations?

It is likely that we evolved on a high-fiber diet due to the unavailability of processing techniques. Some have estimated that our fiber consumption may have been as high as 50 grams daily when fiber-rich foods were more bountiful in our diet. Some current populations in Africa have been noted to retain high-fiber intakes. On the other hand, it is estimated the average American woman and man eats about 15-16 grams and 18-20 grams of dietary fiber daily, respectively.


The Adequate Intake (AI) recommendation for total fiber intake for adults who are 50 years of age and younger is 38 grams per day for men and 25 grams for women daily. For adults over 50 years of age, the recommendation is 30 grams per day for men and 21 grams for women. Or 14 grams per 1000 calories consumed. The introduction of more functional fiber recipes may help increase fiber consumption in the years to come.

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What happens to fiber in the digestive tract?

Contrary to starch, fiber is not broken down well by our digestive enzymes. This is partly explained by the manner in which the mono­saccharides are linked together. Whereas digestive enzymes (amylases) produced by people are very efficient in breaking the links between monosaccha­rides in starch, these enzymes are generally ineffective at breaking the links between monosaccharides in fiber. Plants build these bonds in a special way.


In the stomach the more soluble fibers attract and bind to water and in turn form a gel-like material. This gel entraps food components such as sugars, cholesterol and fats and slowly carries them through the remaining digestive tract. Insoluble fibers, on the other hand, tend not to contribute to the formation of gels. Because soluble fibers dissolve in water, psyllium husk, inulin, FOS and others are used in supplemental fiber drinks.


As fiber reaches the colon bacteria begin to breakdown (ferment) some of the fibers for energy and in the process produce gases such as CO2, methane gas (CH4), and hydrogen gas (H2). These gases often lead to uncomfortable bloating and flatulence associated with higher fiber intakes. Soluble fibers are more fermentable than insoluble ones. Also, other molecules, such as short-chain fatty acids, are produced by bacteria, which can be absorbed into the body. These fatty acids yield a small amount of energy and health benefits. Therefore, foods or supplements providing psyllium, beta-glucan (oats or barley), inulin, FOS, cellulose, guar gum, xanthan gum and oligosaccharides will be fermented and you can expect gas production.


What is diverticulosis and can fiber help?

Diverticulosis is a situation in which there is an out-pouching of the inner wall of the colon. This disorder is believed to be the result of increased pressure within the colon. In turn, this increased pressure is most likely the result of the highly refined diet that people choose to eat in the United States. A refined diet results in less fiber or “roughage” and thus less digestive leftovers or “residue” making its way into the colon. Less content in the colon results in a smaller diameter and greater pressure exerted upon its walls from within. It is a matter of physics, as there is an inverse relationship between the radius (r) of a collapsible tube and pressure (P) as follows:


P = 1/r4


So you see, if the radius of the colon increases due to increased content then the internal pressure decreases, and vice versa. Researchers have clearly shown that those populations in the world that eat more fiber have a lower incidence of diverticulosis. Diverticulosis can lead to a medical concern called diverticulitis. Here the out-pouchings become impacted with bacteria and debris, leading to irritation, inflammation, pain, and sometimes bleeding.


Insoluble fibers like cellulose and hemicellulose appear to have a beneficial effect upon the formation of feces and their evacuation. Bran is an excellent source of these insoluble fibers and explains the popularity of bran breakfast cereals, muffins, and other products among individuals experiencing constipation and diverticulosis. Soluble fibers can contribute to mass and moistness of feces but not to the same extent as insoluble fiber. However, it is important to recognize that both types of fibers are beneficial and should be sought out for general digestive health.



Can fiber promote general gut health?

Beyond diverticulosis, fiber supports general gut health. Certain fibers, particularly soluble fibers, are probiotic. Probiotic nutrients support the health of beneficial bacteria in the digestive tract. These bacteria include bifidobacterium and lactobacillus, which are major types of bacteria found in the digestive tract. There bacteria are linked to improvements in the health of the digestive tract and can decreases the likelihood of gut related issues such as irritable bowel disorders and certain tumors.


Are certain types of fiber good for lowering blood cholesterol levels?

Soluble fibers include beta-glucans, mucilages, pectins, gums, and some hemi­celluloses and are purported to reduce blood cholesterol. Soluble fibers may bind to cholesterol in the digestive tract rendering them unavailable for absorption. Psyllium, oat and barley fiber are among the most advantageous providers of soluble fiber and the Food and Drug Administration (FDA) allows claims on food packages linking the consumption of these fibers to a reduction in cholesterol. Look for the following health claim on a soluble fiber containing food:


"The soluble fiber from psyllium seed husk in this product, as part of a diet low

in saturated fat and cholesterol, may reduce the risk of heart disease."


A product must contain at least 1.7 grams of soluble fiber from psyllium seed husk per serving in order to have the health claim on its label.


Additionally, there is evidence to suggest that the short-chain fatty acids (acetic, butyric, propionic, and valeric acids) and lactate produced in the colon by bacterial breakdown of soluble dietary fibers may reduce cholesterol formation in the liver. Thus, soluble fibers can inhibit cholesterol absorption from the digestive tract as well as cholesterol production in the liver. These two factors may lead to reductions in the level of cholesterol in blood; this will be explored more thoroughly in Chapter 13.


Is fiber good for diabetics?

Fiber is an important to people who have diabetes for a couple of reasons. First, fiber lowers the glycemic index and load of a food by adding bulk. In addition, soluble fibers promote the formation of gels in the stomach which slows the digestion and absorption of carbohydrates. These effects lower the glycemic response of a food and contribute to better blood glucose management. Fiber consumption, particularly whole grains seem to increase insulin sensitivity. That means that the pancreas will be lower throughout the day, which can lower the risk of heart disease. Lastly, fiber promotes satiety and can reduce total food consumption at a meal leading to less carbohydrate and calories consumed. In turn, reducing the number of calories consumed can promote weight loss in overweight people with diabetes which is important since most are overweight, primarily those with type 2.


Can fibers enhance mineral absorption?

Soluble fibers such as inulin and FOS enhance the absorption of some minerals in the colon, namely calcium and magnesium. While researchers are trying to better understand how this occurs, it would seem that there are a couple of possibilities. First, minerals such as calcium and magnesium can bind to fibers further up in the digestive tract. Then when soluble fibers are broken down in colon they are released and available for absorption. The creation of acids (short chain fatty acids and lactate) when soluble fiber is broken down by bacteria decreases the pH of the colon, which in turn enhances the absorption of calcium and magnesium in that part of the digestive tract.


Can fiber support immune function?

In addition to supporting heart and gut health as well as enhancing the absorption of key minerals, dietary fiber can also enhance the immune system. When soluble fibers are broken down by bacteria in the colon the by-products seem to increase the production of T helper cells and antibodies, as well enhance key immune system operations that provide immune protection.


Are there other dietary considerations when eating a high-fiber diet?

Perhaps the most obvious consideration is the production of gases, which may lead to bloating and cramping and the possibility of diarrhea. These symptoms seem to be most common when people who are not fiber consumers increase their fiber intake dramatically. It is recommended that people who are sensitive to fiber and these effects ramp up their intake slowly. Because fiber binds water, which is used to soften stool, there might be an additional need for water. This is easily solved by consuming fiber foods and supplements with water or other fluid.






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