Food sources and Facts of Fiber


Fiber isn’t a single nutrient but a family of plant-based nutrients that are generally resistant to human digestion. Plants lack bony skeletal design which provides much of an animal’s shape or form. In general, fibers contribute much of the structural support to cell walls and the plant. 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.

Mostly, fiber as a class is made up of polysaccharides, but fibers vary from starches insofar as chemical bonds which accompany individual sugar units could not be digested by human enzymes in gastrointestinal tract. This prevents the small intestine from absorbing the sugars because they cannot be released from the various fibers. Fiber is not a single substance but a group of substances with similar characteristics. The group is composed of the carbohydrates cellulose, hemicelluloses, pectins, gums, and mucilages, as well as the non-carbohydrate lignin. Cellulose, hemicelluloses, and lignin form the structural parts of plants.

Bran layers form the outer covering of all grains, so whole grains (i.e., unrefined) are good sources of bran fiber. Bran fiber is rich in hemicelluloses and lignin. (The woody fibers in broccoli are partly lignin.) Because the majority of these fibers neither readily dissolve in water nor are easily metabolized by intestinal bacteria, they are called non-fermentable or insoluble fibers. Insoluble fiber is found in wheat bran, nuts, fruit skins, and some vegetables. Insoluble fiber acts as a natural laxative because it speeds up the transit time of food through the GI tract.

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. Fructooligosaccharides (FOS), which are sometimes called oligofructose or oligofructan, are short links of fructose terminating in glucose.

What Is Soluble and Insoluble Fiber?

Fibers are often classified as being either soluble or insoluble; however, plants tend to contain a mixture of both. 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. As in plums and prunes incorporate both types of fiber with skin it offers more insoluble fiber and fleshy pulp provides more soluble fiber. Psyllium fiber is referred to as a soluble fiber food source although roughly a third of its fiber is insoluble.

Sources of soluble fiber include psyllium husk, barley, oats and legumes and many fruits and vegetables notably apples and pears. Soluble fibers used as food ingredients include inulin, guar gum, FOS, and xanthan gum.

Solubility refers to how well a substance will interact with and dissolve in water. Soluble refers the capacity to form a gel in digestive tract where water is trapped. Supplement drinks of soluble fiber are visual example of the sponge-like properties of soluble fibers.

Food Sources of Fiber

Food name Weight (g) Fiber (g) DV%
Corn bran 76 60 157%
Hyacinth beans 210 53 139%
Winged beans 182 47 123%
Lima beans 202 41 107%
Beans, navy 208 31 81%
Soybeans 172 30 78%
Beans, kidney 184 28 73%
Radishes 116 27 71%
Mammy-apple 846 25 65%
Beans, adzuki 197 25 65%
Wheat bran 58 24 63%
Rice bran 118 24 63%
Spelt 174 18 47%
Yardlong beans 167 18 47%
Nuts, almonds 143 17 44%
Buckwheat 170 17 44%
Millet 200 17 44%
Avocados 230 15 39%
Feijoa 243 15 39%
Pistachio nuts 123 13 34%


What are the recommendations of Fiber intake?

It is likely that we evolved on a high-fiber diet because of 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.

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 1,000 calories consumed.

Health Benefits of Fiber

Let us explore health benefits associated with fiber:

  1. Improve gut health

Beyond diverticulosis, fiber supports general gut health. Soluble fibers are regarded to be probiotic. Probiotic nutrients support the health of beneficial bacteria in the digestive tract. These bacteria include bifido bacteria and lactobacilli, which are major types of bacteria found in the digestive tract. The bacteria promote digestive tract health and lower the chances of gut-related ailments such as irritable bowel disorders or tumors.

  1. Lower blood cholesterol levels

Soluble fibers involve beta-glucans, pectins, mucilages, gums and some hemicelluloses and are implied to lower blood cholesterol. They may bind to cholesterol in digestive tract which makes them unable for absorption. Oat, psyllium and barley fiber are the providers of soluble fiber.

Moreover, evidence suggests that short-chain fatty acids (acetic, propionic, butyric, and valeric acids) and lactate formed in colon by bacterial breakdown of soluble dietary fibers might lower formation of cholesterol in the liver. Hence soluble fibers can curb absorption of cholesterol from the digestive tract and cholesterol production in liver. These two factors may lead to reductions in the level of cholesterol in blood.

  1. Enhance Mineral Absorption

Soluble fibers such as FOS and inulin promotes absorption of some minerals namely magnesium and calcium in the colon. While researchers are trying to better understand how this occurs, it would seem that there are a couple of possibilities. Minerals such as magnesium and calcium can bind to fibers  in the digestive tract. When soluble fibers are crumbled in the colon, they are released and assist 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.

  1. Support Immune Function

Besides it supports heart, gut health and absorption of minerals, it strengthens immune system. As soluble fibers are ruptured by bacteria in the colon, by-products seem to promote the production of T helper cells or antibodies and promote crucial immune system operations which offer immune protection.

  1. Lowers constipation

Dietary fiber helps to lower constipation as it adds bulk to the stool. It makes the bulky feces move faster from gut with increasing stool weight and improved regularity. Stool weight, consistency and frequency of defecation are indicators of colonic activities. Increment of bulk and low transit time are regarded as the beneficial effects of dietary fibers. Various dietary fibers have variety of bulking capacities that depends on underlying mechanism. Unsatisfactory fermented fibers add bulk by promoting water binding. Dietary fibers being fermentable offers bulking effect due to increase in bacterial mass.

  1. Improve regularity

Regularity refers regular expulsion of bulky and soft stools and could be assessed by determining both stool water content and both stool output. An insoluble fiber promotes regularity with stimulation of large bowel to enhance water and mucous secretion while soluble gel forming fibers promote water holding capacity of stool. Fibers enhance stool water content resulting soft and bulky stools making easier to pass. Daily recommended intake of fiber offers numerous health benefits and a single fiber does not provide all benefits. Various fibers are required regularly for functioning of body.

  1. Lower level of blood glucose

Study revealed adhesive fiber is associated to lowering postprandial blood glucose. Reduction of postprandial levels of blood glucose is regarded to be beneficial physiological effects associated to viscous fibers. Gel forming fibers slows down absorption of glucose and other nutrients at intestinal brush border and thus reduces glycemic impact of foods.

  1. Manages weight

Dietary fiber helps to maintain healthy weight. Studies have shown that obese adults consume less dietary fiber in comparison to lean counterparts. Research was conducted to investigate weight management benefits of specific dietary fibers.

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 are experienced when people promote fiber intake suddenly. It is recommended that people who are sensitive to fiber and these effects ramp up their intake slowly. As fiber binds water which helps to soften stool, it might require additional need of water. This is easily solved by consuming fiber foods and supplements with water or other fluid.


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