Introduction:
Dietary fiber (DF) is defined primarily in nutrition science as the edible part of plants and the analogous carbohydrate source that essentially can resist the role of digestion and absorption in the human small intestine and has the innate ability to undergo complete or partial fermentation within the large intestine, as per the information given by the American Association of Cereal Chemists (AACC). Meanwhile, dietary fiber can be either soluble or insoluble. Let us have a look specifically, exploring the essential insoluble dietary fiber (IDF) elements in nutritional science.
How Does Insoluble Fiber Differ From Soluble Dietary Fiber?
Soluble dietary fiber (SDF) is commonly used in the production of global functional foods due to its hydrating as well as easy dissolution properties; on the other hand, insoluble fiber through dietary sources is one of the game changers in boosting public health and immunity at a community level.
Insoluble fibers tend to vary in content across different food groups, with the majority of fresh or frozen fruits and vegetables containing higher amounts of insoluble fiber rather than soluble dietary fiber. The major components of IDF seen in different food groups in nature are primarily plant-based cell wall components such as cellulose (the primary structural component of plant cell walls, contributing to insoluble fiber), certain hemicelluloses (a group of complex carbohydrates found in plant cell walls, contributing to dietary fiber), lignin (a complex organic polymer found in the plant cell wall, providing rigidity and forming part of insoluble fiber), chitin (part of insoluble dietary fiber), chitosan, and resistant starches (types of starch that resist digestion in the small intestine and function as dietary fiber).
IDF is essential for maintaining healthy gastrointestinal function and preventing its related ailments, ranging from common clinical constipation to chronic cases of colonic diverticulosis (formation of small pouches (diverticula) in the colon wall, which can cause digestive issues). Insoluble dietary fibers are mainly attributed to their numerous gastrointestinal health benefits in humans because they are neither water-soluble nor capable of forming gels. As these fibers are not easily fermentable, even in the large intestine, they promote improved bowel movements and bulk stool formation, thereby supporting gastrointestinal health.
Examples of foods rich in IDF include fortified cereals, cereal brans, rice bran, all-bran, and whole grains. These sources are specifically significant in IDF, mainly in plant cellulose and lignins. Wheat bran, on the other hand, typically comprises roughly 50 percent of essential dietary fiber and is extremely cardioprotective, while oat bran is reported to roughly have around 20 percent dietary fiber.
What Are the Benefits of Consuming Insoluble Dietary Fiber (IDF)?
The research on human gut microbiota extensively shows that while fermented SDF foods (soluble dietary fiber foods) have a positive overall impact on both lipid and glucose metabolism, which makes them commonly used in commercial functional food production in the food industry, it is unwise to underestimate the value of insoluble dietary fiber (IDF) either because this is a cornerstone of individual immunity. These insoluble sources cannot be used for commercial purposes owing to their hard molecular structures, ranging from varied food groups such as whole grain cereals, pulses, frozen or fresh fruits, and vegetables, and also include synthetic sources such as polydextrose, hydroxypropyl methylcellulose, and cyclodextrins. These sources are indeed valuable to human health.
As we know, the sources of insoluble dietary fiber are plant foods, and they have several research-based benefits associated with them:
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Consuming more insoluble fiber via diet can help promote regular bowel movements. This is because insoluble fiber can promote increased fecal bulk and improve softness and frequency, preventing constipation by promoting stool regularity.
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Insoluble fiber can have a positive impact both on lipid and glucose metabolism, just like soluble dietary fiber. Research shows that it can enhance lowered blood cholesterol and reduce blood glucose levels easily with regular consumption.
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IDF supports the normal gastrointestinal function of the intestinal tract owing to its ability to produce increased stool weight and also reduce the overall colonic transit time (the time it takes for food to move through the colon, influenced by diet, hydration, and physical activity). This is also one of the added health benefits associated with IDF, which comprises essential plant-based phenolic compounds (polyphenols) and several other types of antioxidants present in the varying food groups, thereby having promising potential in preventing diseases like colonic diverticulosis and constipation.
What Are the Types of Insoluble Dietary Fiber?
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Cellulose: This is one of the major IDF sources found in plant cell walls and also essentially constitutes the cell walls in vegetables, algae, some microorganisms, and more. Cellulose is the insoluble plant polymer consisting of a straight chain of glucose monomers that remain linked through a β-(1 → 4) glycosidic bond. Cellulose is the most prevalent food component found in most whole food sources, be it cereals, fruits, legumes, and vegetables- constituting approximately 25 percent of the dietary fiber in grains and fruits and a notable 33 percent in nuts and vegetables.
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Hemicellulose: These are complex polysaccharide molecules composed of several sugar units such as xylose, mannose, arabinose, glucose, and galacturonic acid, commonly found in cereal grains, with approximately one-third of these essential dietary fiber sources derived from fresh or frozen vegetables, fruits, legumes, and nuts.
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Lignin: This is a major component of woody plant parts such as the outer layer of wheat grains and the celery plants. Lignin is one of the primary active constituents of cell walls, attributed to improved gastrointestinal functioning in humans because of the substance's ability to retain water, promote an increased size of fecal matter, and promote food movement through your small and large intestines.
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Resistant Starches: These are compounds that aid by their prebiotic gut microbiome-boosting nature and hence exert a positive impact on your colonic health. Whole kernel grains, whole grain bread, seeds, pasta, ginkgo starch, green bananas, legumes, raw potatoes, and high-amylose content maize are usually higher in resistant starches.
Conclusion:
Insoluble dietary fiber (IDF) is no less valuable in nutritional value than soluble dietary fiber and has greater potential to boost the individual's systemic health in preventing the individual predisposition to several types of chronic illnesses and lifestyle diseases in today's age. Every individual must have a different food choice when it comes to selecting their food groups from the natural dietary diversity around, with scope for multiple insoluble fiber sources. Therefore, according to most global nutrition experts, you take the counsel of a registered healthcare professional or nutritionist to decide your dietary choices based on your medical history, your nutritional requirements, and your long-term health goals.
