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Dietary fibers and their effects on health

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RESEARCH REVIEW International Journal of Multidisciplinary
e-ISSN: 2455-3085 | Vol.06 | Iss.07 | July 2021 | pp. 35-42
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RESEARCH PAPER
Dietary fibers and their effects on health
*Yousafzai, Mati Ur Rehman
Master of Biological Science and Lecturer, Basic Science Department, Spinghar institute of Higher education,
Nangarhar, Afghanistan
Abstract
There are many observational data that documented the association of lower risk of
cardiovascular abnormalities and dietary fiber consumption. Because humans cannot
digest fibers due to lack of digestive enzyme. Carbohydrates are one of the indigestible
form of dietary fiber. In nature the lignin and dietary fibers are found in plants and
are classified on the basis of solubility as soluble and insoluble fibers. They're found in
several fruits, vegetables, grains, and wheat. There are number of ways present
through which soluble fibers have been shown to help in lowering the blood cholesterol
level. The non-soluble dietary fibers include lignin, hemicellulose, and cellulose; these
fibers are abundant in whole-grain meals, bran, nuts, and seeds. Water-insoluble
fibers may minimize intestinal transit time and increase fecal volume, promoting
digestive regularity, due to their quick stomach emptying. The functional fibers are
isolated and extracted form of dietary fibers that have more fitness benefits when
included to food nutrients during the processing of emptying the stomach.
The daily allowances that are recommended for men and women aged 19-50 are 38
g/day of the total fiber that is consumed per day, discretely. The important point is
that the RDS recommendation is only for fit and healthy peoples and not applicable
on the people having any chronic disorders. According to studies, the majority of
Americans do not follow the RDA instruction of taking dietary fibers strictly. The
present state of knowledge about dietary fiber, fiber sources, and heart disease risk
reduction will be discussed in this review.
Keywords:
Fiber composition; dietary fiber; soluble fiber; non-soluble fiber; groups
of food; cardiovascular disease
Article Publication
Published Online: 15-Jul-2021
*Author's Correspondence
Yousafzai, Mati Ur Rehman
Master of Biological Science and
Lecturer, Basic Science Department,
Spinghar institute of Higher education,
Nangarhar, Afghanistan
mati.chemist[at]gmail.com
10.31305/rrijm.2021.v06.i07.007
© 2021The Authors. Published by
RESEARCH REVIEW International
Journal of Multidisciplinary. This is an
open access article under the CC BY-
NC-ND license
(https://creativecommons.org/licenses/
by-nc-nd/4.0/)
Introduction
The heart disease in United States is one of the leading cause of morbidity and mortality. The report of National
Vital Statistics Service showed that the cerebrovascular disorders were the fifth greatest factor in 2016 of death
(1). For decreasing the level of low-density lipoprotein cholesterol (LDL-C), Statins are found helpful medication
in major cases of atherosclerotic cardiovascular disorders, to date (2). Statins lower blood cholesterol levels by
blocking the 3-hydroxy-3-methylglutaryl-coenzyme A (HMG CoA) Reductase enzyme, this is the third step in the
synthesis of endogenous cholesterol. Non-statin medications were shown to be ineffective in lowering blood
cholesterol in clinical studies due to concerns with toleration or less advantages of fitness (3). Moreover, in case
of required high dose of statin therapy may leads to complications and also expensive. Furthermore, statin non-
adherence and dropout rates have increased, and yet many at-risk patients fail to reach adequate LDL-Cholesterol
reduction with statin mono-therapy (4). The dietary fibers are used with statin as a dietary supplement in
order to enhance the efficacy, health benefits and decrease the dose of statin. The most recent meta -
analysis documented that soluble fiber improves the efficacy of statin (5).
Furthermore, eating whole cereals, which are abundant in dietary fiber, was connected to improved statin
benefits in lowering blood cholesterol, according to NHANES cross-sectional data (20032006) (6). In Germany,
since 1850, Animal feeds have been used to make crude fibers (7).
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During 1954, South African Bantu reported that the decreasing in the cholesterol and lipid level is due to the
effect of dietary fiber (8). Fisher discovered that for a year and a half, cockerel fed a 5% pectin-supplemented
food stored and excreted two times more cholesterol and three times greater fat as cockerel fed a regular food (8).
The research on the effects of dietary fiber on lipid digestion was reported by the cockerel in 1964 (9). The goal
of this review is to emphasize the advantages of soluble gel-forming fiber as a supplement to statins for
decreasing blood cholesterol, which is a symptom of cardiovascular disease.
Metabolism and Chemistry of Fiber
Dietary fibers are high in carbohydrates and lignin, which are not degraded by enzymes present in humans and
hence are not breakdown or suck up (10). Plants have intact dietary fiber, which is made up of from the subunits
of complex polymer of phenylpropanoid. Soluble fiber is a type of fiber present in plants that is not digested
completely but can be converted into pieces in large intestine in the form of short-chain fatty acids by colonic
bacteria. On the other hand, non-soluble fiber, passes through the digestive system without being broken down
(11).
Non-soluble fibers include cellulose, some hemicellulose, and lignin. The hydrogen bond that exists between
glucose residues results in cellulose its three-dimensional structure. Cellulose is an extended linear polymer made
up of β (14) glucose units bonded together.
Hemi-cellulose is made up of hexose and pentose sugars linked by (14) bonds in the backbone and glucuronic,
arabinose, and acid galactose, bonded by β (1–2) and (13) in the side chain. Lignin is made up of highly branched
phenol polymers through well-built intramolecular connections (11). The example of soluble fiber includes pectin,
gums, mucilage made from psyllium husk, β -glucan, and fructans, as well as some hemicellulose.
A heterogeneous polysaccharide Pectin is made up of straight chains of α (1–4)-linked D-galacturonic acid
backbone with pentose and hexose chains attached to it. Gums include a galactose backbone attached by β (13)
and β (1–6) bonds with galactose, methyl-glucuronic acid, glucuronic acid, or arabinose side chains and are
released where injury is present at plant. Mucilage is a sticky, gel-forming liquid-soluble fiber found in the plant
psyllium that contains up to 80% soluble polysaccharide and is structurally similar to gums. β -glucans, and apart
from these, are homopolymers of simple sugar subunits, and fructans, which include oligofructoses and inulin, are
polymers of fructose.
In humans, soluble fiber is sensitive to contamination by enzymes present in small intestine, however, bacteria in
the intestinal tract degrade it into simple fatty acids (SCFA). The creation of SCFA causes changes in the gut flora,
which adds to soluble fiber's hypocholesterolemic effects (12). Dietary fiber fattens up the food, dissolve and
isolate cholesterol, and therefore reduces the consumption capability of liver while boosting the release of bile and
fecal lipids and bile acids.
Fibers in the diet and in the body
Dietary fibers, which comprise both soluble and non-soluble fibers are the important components of a healthy
diet, are carbohydrates and lignin which is not digested found in plants. The primary and secondary walls of the
herb cell wall make up the majority of the dietary fiber content.
Dietary fibers are characterized depending on how well they dissolve in hot water, how much water they can hold
(hydration), and how viscous they are in nature (7,13).
Viscous fibers like -glucans, fructans (inulin, fructooligosaccharides), gum, pectin, and mucilage, as well as non-
viscous fibers like hemicellulose, are all soluble fibers. Soluble fibers store water and form a gel, which slows
digestion by increasing food transit time, delaying stomach digestion process, limiting nutrient uptake, and
delaying digestion. Soluble fiber can be found in vegetables like onion, broccoli, carrots, and artichokes, as well as
fruits like pears, berries, bananas, apples, and oats, legumes, and barley. Non-soluble fibers include lignin,
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cellulose, and hemicellulose. Non-soluble fiber, unlike soluble fiber, reduces transit time and increases fecal
volume, which aids in constipation relief. Insoluble fibers can be found in whole cereals, oats, flour, nuts, and
seeds, as well as a variety of fruits and vegetables. While both soluble and non-soluble fibers are indigestible and
can be digested by bacteria, because of having enzyme for digestion. The soluble fibers can be simply fermented
by gut microbiota and therefore works as a great source of SCFAs. Finally, SCFAs can be entered from colonic
environment and oxidized for the purpose of energy generation. SCFAs entrance has been documented to
decrease the synthesis of cholesterol in liver which in turn contribute to the decrement in blood cholesterol level
and elevated water and sodium entrance into the colonic mucosal cells [14,15].
SCFAs also take part in making acidic colon luminal environment that decreases the dissolvability of free bile
acids, improves the excretion of bile, and reduces the transformation of free bile acids to secondary and more
toxic bile acids. Functional fibers, on the other hand, are indigestible sugars which are obtained, isolated, or
produced and created, and are implicated in positive health consequences in human being. The most common
examples of functional fibers include: β -glucans, cellulose, chitins, and chitosan, fructans, gums, lignin, pectin,
polydextrose and polyols, psylliums, resistant dextrins, and resistant starches [7]. Prebiotics to be considered as a
kind of functional fiber which enhances the host's health by increment in the activity or growth of health-
promoting bacteria in the colon, primarily bifidobacteria and lactobacilli [18]. In order to come under the umbrella of
prebiotics, fibers should resist in digestion via human enzymes and therefore, they must not be hydrolyzed and absorbed; have
the ability to persist in the acidic environment of stomach and finally should be fermented by colon inhabitant bacteria [18]. The
most common examples of prebiotics are Galacto-oligosaccharides, fructooligosaccharides (fructans), and
lactulose.
Intakes of Dietary Fiber Recommendations
Dietary Reference Intake (DRI) daily allowances for males aged 1950 years and women aged 25 years are 38
g/day and 25 g/day, respectively, while for men over 51 years is 31 g/day and women over 51 years is 21 g/day.
19 g/day is recommended for infants ages 13, and 25 g/day is recommended for children ages 48. For 913-
year-old boys, the DRI guidelines are 31 g/day and 38 g/day. The DRI recommendation for girls ages 918 is 26
g/day. Despite the fact that dietary fiber has been demonstrated to provide a number of health benefits, most
Americans consume only 15 grams per day, which is far less than the recommended amount. [19]. Fiber intake
has no maximum limit, but tolerance varies by person, and the most common negative effects of excessive fiber
consumption include bloating and gastrointestinal pain..
Fiber and Cholesterol in the Blood
Studies of Animals
In rats, isomaltodextran treatment was related with lower fat absorption relative to the control vehicle,
and this effect lasted for up to 6 hours [20]. The mechanism was attributed to enhanced micelle stability and larger
particle size, according to the authors. In guinea pigs, our team discovered that feeding pectin, guar gum, or
psyllium boosted LDL-ApoB 100 turnover, which resulted in upregulation of hepatic LDL receptors, resulting in
quicker catabolism and elimination [2125]. Furthermore, fiber's hypocholesterolemia effect was due to a decrease
in the number of secreted VLDL particles, as well as a decrease in cholesteryl ester transfer protein (CETP)
activity, resulting in lower cholesteryl ester in VLDL particles that are transferred to LDL, and increased VLDL
and LDL apo B 100 turnover [21]. Dietary fibers have been shown to reduce the risk of heart disease and the
mortality associated with cardiovascular disease in a variety of animal models. Lo et al. (1987), for example, found
that soybean dietary fiber was helpful in reducing atherosclerosis in rabbits [26].
Similarly, grapefruit pectin was found to decrease atherosclerosis in miniature swine by Beakey et al. (1988)
[27]. For 3.5 years, McCall et al (1992) compared the intake of low-cholesterol cellulose (LCC), high-cholesterol
psyllium (HCP), and high-cholesterol cellulose (HCC) in African green monkeys, finding that both LCC and HCP
greatly decreased blood cholesterol compared to HCC, and that dietary psyllium decreased total blood cholesterol
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by lowering LDL cholesterol formation [28,29]. In rats, Roach and Topping et al. (1990, 1992) found that
combining oat bran and fish oil reduced blood cholesterol levels [30,31]. Wilson and colleagues also discovered
that in Syrian Gold Hamsters, barley and insoluble fibers had a hypocholesterolemia impact [3234]. Similarly,
multiple studies have shown that particular forms of dietary fiber can help mice lower their blood cholesterol levels
[3541]. Studies in animal models show that both soluble and insoluble fibers are important in lowering blood
cholesterol, reducing atherosclerosis, and lowering the risk of heart disease.
Studies on Human
Observational Studies
Several cohort studies in the United States and around the world have looked at the relationship between
dietary fiber intake and coronary heart disease and cardiovascular disease [4253]. Dietary fiber was found to have
a preventive effect against heart disease in these trials. Pereira et al. (2004) performed a meta-analysis of ten
cohort studies with a follow-up period of 610 years [44]. With a Relative Risk (RR) of 0.84 (95 percent CI, 0.70
0.99), the researchers found an inverse connection between dietary fiber consumption and the risk of
cardiovascular disease. However, an increase in fiber consumption of 10 grams per day had no statistical
significance, with a relative risk of 1.0 (95 percent CI 0.881.13). Threapleton and colleagues (2013) conducted a
meta-analysis to assess the doseresponse association between dietary fiber consumption and cardiovascular disease
risk [54]. The pooled preventive impact for each 7 g/day increase in fiber consumption was RR = 0.91, according
to the researchers (CI 0.87 to 0.94). Higher fiber doses, on the other hand, exhibited a wider confidence interval
around the mean, making the findings less credible [54]. Furthermore, in the Prevencion con Dieta Mediterranea
(PREDIMED) trial, Buil-Cosiales and colleagues (2014) found that fruit fiber intake was linked to lower all-cause
mortality (Hazard Ratio 0.59, 95 percent CI = 0.44, 0.78) [55]. Throughout the last three decades, several
researchers have demonstrated the benefits of dietary fiber from a diversity of food causes in reducing the risk of
heart disorders. [54,5662]. As a result, founded on the information, it seems that fiber intake should be limited.
Bias and confounding variables are two major drawbacks of observational research [62], In addition,
rather than demonstrating causation, relationships and correlations are shown. Assortment preference can occur
in cohort studies as a result of instructive editing and quantity mistakes, and in case-control studies as a result of
inadvertent control selection. Confounding may emerge as a result of the coexistence of exposures that result in
the same health effect. It's difficult to account for confounding unless you know all of the frequent reasons of
coverage and their links to the illness results. To explore the interconnection of fiber in decreasing heart disease,
death and to minimize confounders, size faults, and choice preference, trials with a randomized control group
investigations are done (63).
Other Functions of Fiber
Dietary fiber protects against chronic infections such heart disease, diabetes, metabolic condition, irritable bowel
disorder, diverticular disease, obesity, and colon cancer in an age-adjusted study. Insoluble fiber, for example,
impasses to and adsorbs carcinogens, mutagens, and poisons, reducing their negative special effects on the body
by blocking contaminants from being absorbed and directing them to be eliminated. Delay in intestinal passage
period, prolonged satiety and satiation after a meal, and production of the cholecystokinin, leptin are all fiber
features. Increasing fiber intake by eating more whole grains, fruits and vegetables, nuts and legumes, according to
the Academy of Nutrition and Dietetics, is associated to a subordinate risk of type 2 diabetes, cardiovascular
disease, and certain malignancies [64].
Conclusion
Dietary fiber would be used to supplement statin monotherapy in decreasing entire and Low Density
Lipoprotein-Cholesterol, as well as to decrease the statin intake, reduce adverse effects, and improve drug
acceptability. Dietary fibers in whole foods, both soluble and insoluble, have a variety of non-nutritive fitness
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properties that help to improve lipoprotein outlines and have no caloric value, so they can be included in a
balanced intake design. Whole grains, protein foods, fruits, and vegetables have a lot of dietary fiber, which makes
them particularly suitable for disease anticipation and lowering the risk of cardiovascular disease and
atherosclerosis.
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