DIETARY FIBERMoksha Chib13FET1003

What is Dietary Fiber ? ▪ “Dietary fiber consists of remnants of edible plant cells, polysaccharides, lignin and

associated plant substances resistant to digestion by the alimentary enzymes of humans.”

▪ Resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine

Dietary

FiberSoluble Insolubl

e

Classification based on water solubility/ fermentabilityCharacteristic

Fiber Component

Description Food Sources

Water insoluble/ less fermentable

Cellulose • Main structural component of plant cell wall• Insoluble in conc. Alkali• Soluble in conc. acid

Plants ( vegetables, sugar beet, various brans)

Hemicellulose • Cell wall polysaccharide • Contain backbone of β-1,4 glycosidic linkages• Soluble in dilute alkali

Cereal grains

Lignin • Non carb cell wall component• Complex cross-linked phenyl propane polymer• Resists bacterial degradation

Woody plants

Water soluble/ more fermentable

Pectin• Component of primary cell wall with D-

Galacturonic acid as principal component• Water soluble • Gel forming

Fruits, vegetables, legumes, sugar beet, potato

Gums • Secreted at site of plant injury by secretary glands

• Food & pharmaceutical use

Leguminous seed plants (guar, locust bean), seaweed extracts (carageenan, alginates), microbial gums (xanthan, gellan)

Mucilages • Synthesized by plant, prevent desiccation of seed endosperm

• Food industry use, hydrophilic, stabilizer

Plant extracts ( gum acacia, gum karaya, gum tragacanth)

• Viscous polysacc. Impede absorption of nutrients

• More branching & ionic groups increase solubility

• Porosity & surface area influences extent of fermentation

• Coarser the particle size, more effective it is in increasing the stool output

• Hydration increases with decrease in particle size

• Affects transit time, fecal excretion & fermentation

• Sugar residues associate with H20 molecules by H-bonds

• Insoluble fiber hold onto water & give fecal mass greater water content

• Hydration allows for formation of gel matrix Water

holding capacity

Particle Size

Viscosity &

solubility

Surface Area

Physico-chemical properties of Dietary Fiber

Food Sources

Flaxse

ed

White b

eans,

raw

Bitter

Gourd

Wheat

(Who

le gra

in)

Lentil,

raw

Almon

ds Oats

Sesam

e see

d

Beetr

oot

Brocol

li, raw Kiw

i

Spina

ch

Bana

nas

02468

101214

Dietary Fiber content of various food sources (g/100g edible portion)

Insoluble FiberSoluble Fiber

Fate of dietary fiber in the human digestive system

Stomach• Dietary fiber mixes with partially

digested food in the stomach

Small Intestine

• Not hydrolyzed by pancreatic amylases• Soluble fiber entraps sugar, cholesterol &

fat, hence slowing their absorption in the body

• Hydration of fiber allows for formation of gel matrix & increases viscosity of food mass

Large Intestine

• Polysaccharide fibers metabolized by bacteria inhabiting the LI & create short chain fatty acids (acetic, propionic & butyric acids or VFAs), H2, CO2 & biomass

• Promote regularity & aid in bulking

Fermentation of fiber in colon

▪ Colonic fermentation is an efficient digestive process since starch is almost totally degraded. Usually, more than half of the consumed fibers are degraded in the LI, rest being excreted in the stool

▪ Factors affecting utilization of fermentable sugars are:

o Solubility: More soluble substrates, being more accessible to hydrolytic enzymes are likely to be degraded rapidly

o Digestive motility & individual differences in microflora can also modulate fermentation

DIETARY FIBER

FERMENTABILITY (%)

Cellulose 20-80Hemicellulose 60-90Pectin 100Guar gum 100Ispaghula 55Wheat bran 50Resistant starch 100Inulin, oligosaccharides

100 (if they are not in excess)

▪ Polysaccharides cannot penetrate in the bacterial cell, they are hydrolysed by the membranous or extra cellular enzymes secreted by bacteria

▪ Monomeric sugars are metabolised in the bacterial cells using the EM pathway which leads to pyruvate

▪ Pyruvate does not appear in the large bowel & is immediately converted to end products: SCFA ( acetate, propionate, butyrate) & gases like H2, CO2, CH4

Absorption & metabolism of end products▪ A part of the fermentation products are utilized by bacteria yielding energy & carbon necessary

for synthesis and growth of flora▪ Another part is eliminated in the stool▪ Major part is absorbed by the colonic mucosaShort Chain Fatty Acids (SCFA)

▪ Absorption of SCFA is rapid & leads to accumulation of bicarbonates and increase of pH in the lumen

▪ SCFA stimulate proliferation of colonic epithelial cells & growth of colon in general▪ SCFA, not metabolized in mucosa, is oxidized in the liverGases

▪ Only a fraction of gases are available for absorption, H2 and CH4 are excreted as breath gases.▪ Large part of gases are consumed in the colonic lumen by the bacteria. Unused gases are

excreted.

TYPE OF BACTERIA

SUBSTRATE PRODUCT

Acetogenic CO2 and H2 AcetateMethanogenic

CO2 and H2 CH4

Sulfate reducing

Use H2 to reduce sulfates

Sulfites or H2S

Type of bacteria in the colon that utilize the gases produced as a result of fermentation

Health BenefitsFUNCTIONS BENEFITSAdds bulk to the diet, making feel fuller May reduce appetiteAttracts water & turns to gel during digestion, trapping carbs & slowing absorption of glucose

Lowers variance in blood sugar levels

Lowers total & LDL cholesterol Reduces risk of heart diseasesRegulates blood pressure May reduce onset risk or symptoms of

metabolic syndrome & diabetesSpeeds the passage of foods through the digestive system

Facilitates regularity

Adds bulk to stool Alleviates constipation Balances intestinal pH & stimulates intestinal fermentation production of SCFA

May reduce risk of colorectal cancer

Effects on carbohydrate digestion & absorption

Gastric emptying• They may slow gastric filling,

due to bulking & energetic dilution capacity

• Soluble fibers on mixing with liquid meals, delay emptying of gastric liquids by increasing viscosity of gastric contents

• Insoluble fractions may also alter gastric emptying by mechanisms depending on their water retention capacity or size of particle

Lowers postprandial glycaemia

• Due to its WHC, dietary fiber absorbs water and forms a gel

• The gel entraps carbohydrates and lowers absorption of glucose

• Thus the blood glucose levels do not shoot up after meals and are maintained

Effects of fiber on large bowel function

Stool output• Least fermentable show the

greatest effect on stool output• Dietary fibers with high WHC are

more fermentable & are lost before they reach the rectum (exception: ispaghula)

• For a large effect on the stool output, the fiber should simply appear in the stool

• The rest then depends upon the amount of fiber present in the stool

• Dietary fiber also has a role in changing the consistency of the stool by increasing the water content, plasticity & stool frequency

Colonic motility & transit time

Other health benefits

Weight Control• Prevent weight gain or promote

weight loss by extending the feeling of fullness after a meal

• Average weight reductions were found to be greatest for fructans and marine polysaccharide groups

Diverticular disease• High fiber intakes have been

associated with a decreased risk of Diverticulosis, a common condition that is characterized by the formation of small pouches in the colon

• Men with the highest insoluble fiber intakes, show a 37% lower risk of developing symptomatic diverticular disease

• Protective effect of DF against the disease was strongest for cellulose & lignin

Reduction in risk of Cancers

COLORECTAL CANCER▪ Incidence of colorectal cancer was found to be lower in people with high fiber intakes▪ Even though the protective effect of fiber consumption on the occurrence of colorectal

cancer is still questionable, but it has been shown that the supplementation of psyllium resulted in a significant decrease in it

BREAST CANCER▪ It was found that the women with the highest fiber intakes had a risk of breast cancer

40% lower than women with lower fiber intakes▪ The results of small, short-term intervention trials in premenopausal and postmenopausal

women suggest that low-fat (10%-25% of energy), high-fiber (25-40 g/day) diets could decrease circulating estrogen levels by increasing the excretion of estrogens and by promoting the metabolism of estrogens to less estrogenic forms 

Functional Fiber▪ Consist of isolated, non digestible carbohydrates that have beneficial

physiological effects on humans▪ May be non digestible carbohydrates that have been isolated or

extracted from a plant or an animal source, or may be manufactured/ synthesized

PSYLLIUM: Viscous mucilage isolated from the husks of psyllium seeds

CHITIN: Non digestible carb extracted from exoskeleton of crustaceans, long polymer of acetylated glucosamine units linked by β 1,4 glycosidic bonds CHITOSAN: Non digestible glucosamine polymer produced by deacetylation of chitin

FOS: Short synthetic fructose chains terminating with glucose units

RESISTANT DEXTRINS: Indigestible polysaccs formed when starch is heated & treated with enzymes

INULIN: Fructans terminating with glucose units, found in roots & rhizomes of plants like chicory

Synthesis of Inulin from Chicory Roots

Chicory Roots

Washing

SlicingSun Drying (30-

35°C) or Hot Oven Drying (80-90°C)

Grinding to get a chicory powder

Extraction by diffusion in hot water (70-80°c

for 1 hr)

Filtered using a double layer muslin cloth

Precipitation of filtrate using 20,40, 60%

ethanol

Inulin obtained by

centrifugation & dried at 45°C

Synthesis of Chitin & Chitosan

Marine Crustacean

ShellsDemineralizati

on Deproteination Discoloration

ChitinDeacetylationChitosan

HCl NaOH

KMnO4

NaOH (40-50%)

Drug- nutrient interactionsINTERACTION WITH TYPE OF DRUG

RESULTS

Drugs acting on nervous system

• Lithium ingested ispaghula decreases the blood levels of the drugs, fiber also reduced the absorption of lithium

• High fiber diet led to decrease in the serum levels of antidepressants• Consumption of fiber supplements (wheat bran) with Levodopa (drug used

for treatment of Parkinson’s disease) led to elevation of levodopa plasma levels

Lipid lowering drugs • Gemfibrozil administered with guar gum resulted in higher lipid lowering effect. Reduction in total and LDL cholesterol was greater

• In cholesterol-fed hamsters, greater decrease in LDL cholesterol levels were found in animals receiving Cholestyramine with psyllium than in hamsters receiving the drug alone

• Pectin reduces the intestinal absorption of Lovastatin, the cholesterol lowering agent

Hypoglycaemic agents

• Glucomannan may influence the intestinal absorption of Glibenclamide, diminishing the bioavailability of the drug

Drugs acting on cardiovascular system

• Addition of wheat bran lowered Digoxin plasma levels

Anitmicrobials & Chemotherapeutic agents

• Rifamixin improves the benefits of dietary fiber by preventing its bacterial degradation

Nutrient- nutrient InteractionsIt has been observed that increase in the dietary fiber intake decreases the absorption/bioavailability of most of the minerals in the body.

MINERAL/MINERAL BINDING FACTOR

MECHANISM

Oxalate Oxalate & dietary fiber bind to the mineral to form DF-mineral-oxalate complex which is less easily broken down during digestion, thus decreasing bioavailability of the mineral

Tannins Bind Fe by forming insoluble iron tannates leading to impaired heme-iron absorption

Iron Tannins & phytates present in the bran impair Fe absorption. Both heme & non heme Fe absorption is impaired due to the chelating property of phytates

Zinc Rye, barley, oatmeal , triticale, rick sources of phytates hamper the absorption of Zn. Resistant starch in cornflakes chelates minerals

Calcium & Copper Wheat bran constitute phytates Chromium Cr is not bound by phytates, doesn’t show any altered uptake

Role of dietary fiber in absorption of Phenolic Compounds

Role of dietary fiber in absorption of Carotenoids

Adequate Intake for Total Fiber

LIFE STAGE AGE MALES (g/day) FEMALES (g/day)

Infants 0-6 months Not Determined Not DeterminedInfants 7-12 months Not Determined Not Determined

Children 1-3 yrs 19 19Children 4-8 yrs 25 25Children 9-13 yrs 31 26

Adolescents 14-18 yrs 38 26Adults 19-50 yrs 38 25Adults 51 yrs and older 30 21

Pregnancy All ages 28Breast feeding All ages 29

Adverse effects & Safety MeasuresDIETARY FIBERSome people experience abdominal cramping, bloating or flatulence on abruptly increasing the DF intake. These can be minimized by increasing the DF intake gradually & increasing the fluid intake to at least 2 liter/day

ISOLATED FIBERS & FIBER SUPPLEMENTS▪ Gastrointestinal symptoms: Use of guar gum, inulin, FOS, RS & psyllium can cause

gastrointestinal distress. Guar gum containing supplements for weight loss have been associated with esophageal & small bowel obstruction

▪ Colorectal Adenomas: Supplementation with 3.5g/day psyllium for 3years can result in significant increase in colorectal adenomas

▪ Allergy & Anaphylaxis: People with shellfish allergies should avoid supplements with chitin/chitosan in it. Intravenous administration of inulin as well as ingestion of margarine containing inulin extracted from chicory can lead to Anaphylaxis

Marketed Products

Amway Nutrilite Fiber (0.2kg)

Acacia Fiber (Ayurvedic Digestion Support)

NutriCology Dietary Fiber Cellulose

Apple Fiber with Apple Pectin

Marketed Products

Psyllium Husk Caps Fiber Choice Weight Management Tablets

BarnDad’s Fober DX- German Chocolate Shake

Oat Bran (250 tablets)

Yummi Bears Fiber (60 gummies)

References▪ (Food Science and Technology) Susan Sungsoo Cho-Handbook of Dietary Fiber Food Science and Technology-CRC Press (2001)▪ (GWUMC Department of Biochemistry Annual Spring Symposia) D. A. T. Southgate (auth.), George V. Vahouny, David Kritchevsky

(eds.)-Dietary Fiber in Health and Disease-Springer US (1982)▪ Role of Dietary Fiber in the Bio accessibility and Bioavailability of Fruit and Vegetable Antioxidants by Hugo Palafox Carlos, Jesus

Fernando Ayala-Zavala, Gustavo A. Gonzalez- Aguilar (Concise Reviews in Food Science)▪ Dietary Fiber in foods: a Review by Devinder Dhingra, Mona Michael, Hradesh Rajput, R.T Patil in J Food Sci Technol (May- June

2012) 49(3):255-266, DOI 10.1007/s13197-011-0365-5▪ Dietary Fiber and mineral Bioavaialbility by Barbara F. Harland, Department of Human Nutrition and Food, School Of Human

Ecology, Howard University, Washington DC, 20059, USA (Nutrition Research Reviews (1989), 2, 133-147)▪ Handbook of Nutraceuticals and functional Foods, 2nd edition, Edited by Robert C. Wildman▪ Jan Willem van der Kamp_ Julie Jones_ Barry McCleary_ David Topping-Dietary fibre_ New frontiers for food and health-

Wageningen Academic Publishers (2010)▪ Robert R. Selvendran, A. Verena F. V. Verne (auth.), David Kritchevsky, Charles Bonfield, James W. Anderson (eds.)-Dietary Fiber_

Chemistry, Physiology, and Health Effects-Springer US (1990)▪ Dietary fiber and its interaction with Drugs by A. González Canga, N. Fernández Martínez, A. M.ª Sahagún Prieto, J. J. García

Vieitez, M.ª J. Díez Liébana, R. Díez Láiz and M. Sierra Vega▪ TheVitaminShoppe for various marketed goods