What is fibre?
- non-digestible portion of plants
- animal fibre -> collagen and keratin
- food additives
Plant cell wall = 95% of dietary fibres - primary and secondary wall
- cellulose and hemicellulose
- lignin -> structural support
- pectins -> intracellular cement, btw and around the cell walls
Dietary fibre
consists of non-digestible carbohydrates and lignin that are intrinsic and intact in plants
Functional fibre
consists of isolated, non-digestible carbohydrates that have beneficial physiological effects in humans
Cellulose
- dietary and functional fibre
- B 1-4 linked glucose units
- main component of plant cell walls
- water-insoluble
- poorly fermented by colonic bacteria
- ex. bran, legumes, nuts, peas, root veggies
Hemicellulose
- dietary fibre; component of cell walls
- B 1-4, a 1-2; a 1-3 glycosidic bonds
- sugars in side chains determine characteristics
- water soluble or insoluble
- fermentability varied
Pectin
- a 1-4 galacturonic acid
- dietary and functional fibre
- part of plant cell wall
- water soluble with ion-binding potential, gel-forming
- completely metabolized by bacteria
- citrus fruits
Ligning
- phenol units
- dietary and functional fibre
- a structural component of plants
- insoluble in water, poorly fermented
- metabolized or enterolactone
- strawberry
Gums
- B 1-3 galactose, B 1-6 galactose
- dietary and functional fibre
- secreted at the site of plant injury
- water double and highly fermented by bacteria
- uses as a gelling, thickening agent
- oatmeal, barley
Beta-glucans
- B-D-glucopyranosyl (B 1-4 and 1-3 linkages)
- dietary and functional fibre
- water-soluble
- reduce serum cholesterol, postprandial blood glucose
- highly fermentable
- forms viscous gels w/in the GI tract
- oat products
Resistant Starch (RS)
- cannot be easily enzymatically digested and absorbed by humans
RS1 = whole or partially milled grains and seeds
RS2 = potato, unripe banana, maize, some legumes ‘
RS3 = cooked/cooled starchy foods (growth of beneficial bacteria, improved glycemic response)
RS4= chemical modification of starch
Fructans
(insulin, oligofructose, fructooligosaccharides)
- fructose units
Promotes growth of bifidobacteria (prebiotic)
- Dietary fibre
- artichokes, onions, chicory, wheat
Chitin and Chitosan
- B 1-4 glucose units
- insoluble functional fibre
- bind dietary lipids in the stomach
- binds unesterified cholesterol and phospholipids promoting their exception in the feces
- reduce serum cholesterol
- immune enhancing function
Psyllium
- binds water = adds viscosity
- function fibre
- promote a reduction in serum lipids
What are the major physiological effects of fibre?
- Some fibres form a gel:
- delay and lower nutrient absorption
- earlier satiation - other fibres
- speed up and digestion
What are the factors affecting physiologic and metabolic properties?
- Solubility in water
- Water Holding Capacity
- Adsoprtion or binding ability
- Degradability or fermentability
Solubility in water
Soluble:
- delay gastric emptying
- inc., transit time (slower movement)
- dec., nutrient absorption
Insoluble:
- inc. fecal bulk
- dec. transit time (speed up movement)
- dec., of nutrient absorption
Water Holding Capacity
the ability of fibre to bind water as it moves through the GI tract
- describes how much fibre can act as a sponge
Impact:
- pH of GI tract/bolus/chyme
- size of particle
- level of food processing
1. delayed gastric emptying
- slows down movement
2. Reduced missing chyme with digestive enzymes
- gel acts as a ‘physical barrier’ preventing digestive enzymes from assessing the foods
3. Reduced enzyme function
4. Decreased nutrient diffusion
- thickness of the water layer on the surface of enterocytes
- dec. peristaltic movements
5. transit time
Adsorption or binding ability
ability to bind inorganic and organic molecules, for ex., enzymes or nutrients
A. Diminish absorption of lipids
- Type of fibre: soluble fibres
- interact w/ fatty acids, cholesterol, bile acids -. prevents the formation of micelles
B. Increased fecal bile exertion
- Type of fibre: soliuble fibre
- absorbs bile acids preventing recirculation and use of formation of micelles
C. lowered serum cholesterol concentration
- Type of fibre: Psyllium, B-glucans
- 1) inc., bile/cholesterol exertion -. dec. cholesterol in the liver -> more LDL
- 2) bile commotion changes -> inhibits HMG CoA reduction -> synthesis of cholesterol
- 3) production of short-chained fatty acids -> inhibits cholesterol and fatty acids synthesis
D. Altered mineral, carotenoid, and phytochemical
- Type of fibre: hemicellulose, pectins, gums,
- enhance or inhibits mineral absorption -> degree of fermentatively
- slows fermentable fibre -> inhibitory effect
- rapidly fermentable -. enhancing effect
