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The new normal-Globe and Mail- 30 September 2012parents do not recognise when they and/or others
including kid(s) is/are overweight or obese
Fat is the new normal
Lecture 4a- 29 September 2014
Fibre metabolism and regulation
Most of this lecture derived from Chapter 4 of
Gropper
Outline of lectures 4a,b
Definition of Dietary Fibre
Plants and Fibre
Dietary Fibre
Outline of lectures 4a,b
Some Properties-dictate physiological and
metabolic effects of fibre
a) Water Solubility
b) Water Holding/Hydration Capacity as
well as viscosity
Slowed Gastric emptying
Reduced mixing of gastrointestinal
contents with digestive enzymes
Reduced enzyme function
Decreased nutrient diffusion rate
Altered small intestine transit time
Outline of lectures 4a,b
Some Properties-dictate physiological and
metabolic effects of fibre
c) Absorption or Binding Ability
Diminished absorption of lipids
Increased faecal bile excretion
Lowered serum cholesterol
Altered mineral balance
Outline of lectures 4a,b
Some Properties-dictate physiological and
metabolic effects of fibre
d) Degradability or fermentability
Fermentable fibres
Increased water and sodium absorption
in colon
Mucosal cell proliferation
Provision of energy
Acidification of luminal environment
Non-fermentable fibres
Detoxification
Increased faecal bulk
Outline of lectures 4a,b
Recommended Intake of Fibre
Implications in Disease Prevention and
Management
Fibre-Based Herbal Medicines
Outline of lectures 4a,b
Summary
More detailed information
Definition of Dietary Fibre
-not a single entity and therefore no universal
definition
-one attempt at definition- "plant
polysaccharides and lignin which are
resistant to hydrolysis by the digestive
enzymes of man"- Trowell et al quoted in
Chapter 5, Gropper 3rd edition
-however, there are problems with this
definition
Problems with definition-direct quote
from Gropper, Chapter 5
“fails to include all the digestible residue
from food that may reach the colon.
It uses the ability to be digested as the basis
for the definition when undigested food
reaching the colon does not necessarily lack
the ability to be digested
nor is it necessarily unavailable to the body”
Health Canada-2010 definition (most recent)
Dietary Fiber Consists of naturally occurring edible
carbohydrates (DP > 2) of plant origin that are not digested and
absorbed by the small intestine and includes accepted novel
dietary fibers.
Novel Dietary fiber is an ingredient manufactured to be a source
of dietary fiber. It consists of carbohydrates (DP > 2) extracted
from natural sources or synthetically produced that are not
digested by the small intestine. It has demonstrated beneficial
physiological effects in humans and it belongs to the following
categories:
a) Has not traditionally been used for human consumption to any
significant extent, or
b) Has been processed so as to modify the properties of the fiber,
or has been highly concentrated from a plant source
Includes resistant oligosaccharides, resistant starch and resistant
maltodextrins
Plants and Fibre
-fibre is derived from plant cells
-plant cell wall contributes more than 95
percent of dietary fibre
-figure 5.1 –Gropper
-figure 5.3-Gropper
Plants and Fibre
Plants and Fibre
Fibrewater insoluble and water soluble
Fibrewater insoluble
-cellulose-bran, legumes, peas, root vegetables,
cabbage family veggies, apples, outer
covering of seeds
-poorly fermented generally
Fibrewater insoluble
-hemicellulose-not water soluble if do
NOT have acid side chains
-bran and whole grains(not clear if water
or water insoluble or both)
-fermentability depends on sugar and acid
composition-eg hexose and uronic acid are
more accessible to bacterial enzymes
Fibrewater insoluble
lignin-a non-carbohydrate component of fibrewheat,
fruits with edible seeds (eg strawberries) ,
mature root veggies (eg carrots)
-poorly fermented
Fibrewater soluble
-water soluble-refers to hot water
Fibrewater soluble
-water soluble-refers to hot water
-hemicellulose-water soluble if have acid
side chains
Fibrewater soluble
-pectin-gel forming
-apples, strawberries
and citrus fruits
-easily fermented
Fibrewater soluble
-gums
-oatmeal, barley and legumes
-eg: gum arabic
-easily fermented
Fibrewater soluble
-mucilages
-similar in structure to gums
-synthesised by plant secretory cells
-carrageenan and agar-dervived from
seaweed and algae
-used as stabilisers in ice cream
for example
-degraded by colonic bacteria
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
a) Water Solubility
-generally water soluble
-delay gastric emptying
-increase transit time
-decrease nutrient (glucose
absorption)
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
a) Water Solubility
generally water insoluble
-decrease transit time
-increase faecal bulk
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
b) Water Holding/Hydration Capacity as well as
viscosity
-ability of fibre in food to bind water-ie
sponge effect
-water soluble fibres have greater hydration
capacity than?
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
b) Water Holding (whc)/Hydration Capacity
as well as viscosity
-water holding capacity dependent on water
solubility, pH of gastrointestinal tract, size of fibre
particles and degree of food processing
-increased pH increases whc
-coarsely ground bran has higher
hydration capacity
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
b) Water Holding/Hydration Capacity as well as
viscosity
-water holding by fibre creates viscous
solutions resulting in:
Slowed gastric emptying-satiety
Reduced mixing of gastrointestinal
contents with digestive enzymesphysical barrier
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
b) Water Holding/Hydration Capacity as well as
viscosity
-water holding by fibre creates viscous solutions
resulting in:
Reduced enzyme function
-eg inhibit -intestinal peptidases
-pancreatic lipase
-mechanism is unclear
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
b) Water Holding/Hydration Capacity as well as
viscosity
-water holding by fibre creates viscous solutions
resulting in:
Decreased nutrient diffusion rate and hence
nutrient absorption
-passage through mucin layer is
reduced
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
b) Water Holding/Hydration Capacity as well as
viscosity
-water holding by fibre creates viscous solutions
resulting in:
Decreased nutrient diffusion rate and hence
nutrient absorption
-reduced convective currents
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
b) Water Holding/Hydration Capacity as well as
viscosity
-water holding by fibre creates viscous solutions
resulting in:
Decreased nutrient diffusion rate and hence
nutrient absorption
-results in decreased absorption of amino
acids and fatty acids due to viscous
fibre
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
b) Water Holding/Hydration Capacity as well as
viscosity
-water holding by fibre creates viscous solutions
resulting in:
Decreased nutrient diffusion rate and hence
nutrient absorption
-pectin, psyllium and viscous
mucilaginous gums (eg guar gum)
lower blood glucose and hence hormonal
response to glucose
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
b) Water Holding/Hydration Capacity as well as
viscosity
-water holding by fibre creates viscous solutions
resulting in:
Altered small intestine transit time
-soluble -increase transit time- good- why?
-insoluble-decrease transit time- bad-why?
-net effect?
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
c) Absorption or Binding Ability
-lignins, gums, pectins and some
hemicelluloses have ability to
bind(adsorb) enzymes, nutrients in gi
tract
-dependent on gi pH, particle size,
food processing and
fermentability
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
c) Absorption or Binding Ability
-lignins, gums, pectins and some
hemicelluloses have ability to
bind(adsorb) enzymes, nutrients in
gi tract
-results in-diminished lipid absorption
-lowered blood cholesterol
-increased faecal bile excretion
-changed mineral balance
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
c) Absorption or Binding Ability
-lignins, gums, pectins and some
hemicelluloses have ability to
bind(adsorb) enzymes, nutrients in
gi tract
Diminished Absorption of Lipids
-pectin, guar gum, oatbran, lignin- adsorb
fatty acids, cholesterol, bile acids
-consequence of such adsorption
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
c) Absorption or Binding Ability
-lignins, gums, pectins and some
hemicelluloses have ability to
bind(adsorb) enzymes, nutrients in
gi tract
Diminished Absorption of Lipids
Increased faecal bile excretion
-similar mechanistic consequence
seen under diminished
absorption of lipid
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
c) Absorption or Binding Ability
-lignins, gums, pectins and some
hemicelluloses have ability to
bind(adsorb) enzymes, nutrients in
gi tract
Lowered serum cholesterol
consequently more plasma cholesterol
is used to synthesise
bile
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
c) Absorption or Binding Ability
-lignins, gums, pectins and some
hemicelluloses have ability to
bind(adsorb) enzymes, nutrients in
gi tract
Altered mineral balance
-fibre containing uronic acid can
form cationic bridges with
minerals
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
c) Absorption or Binding Ability
-lignins, gums, pectins and some
hemicelluloses have ability to
bind(adsorb) enzymes, nutrients in
gi tract
Altered mineral balance
-lignins also thought to play a role
-slower the fermentation the
higher the ability to bind
minerals by bacteria
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
c) Absorption or Binding Ability
-lignins, gums, pectins and some
hemicelluloses have ability to
bind(adsorb) enzymes, nutrients in
gi tract
Altered mineral balance
-more rapidly fermentable fibres eg
pectin may have positive effect on
mineral balance
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
d) Degradability or fermentability
-principal metabolites of fibre and undigested
starch fermentation are lactate and short
chain fatty acids (SCFAs)
-also get some hydrogen, CO2 and methane gases
-pectin, gums, oat and wheat bran and psyllium
produce SCFAs
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
d) Degradability or fermentability
Fermentable fibres
Increased water and sodium absorption in
colon
-SCFA rapid absorption stimulates
water and sodium absorption
Dietary Fibre
Some Properties-dictate physiological and metabolic effects of fibre
d) Degradability or fermentability
Fermentable fibres
Mucosal cell proliferation
-substrates from degradation of
dietary fibre
Provision of energy
-SCFAs
Acidification of luminal environment
-SCFAs-calcium more available to bile and
fatty acids- may be protective against
colon cancer
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
d) Degradability or fermentability
Non-Fermentable fibres
-principally cellulose and lignins-promote
proliferation of colonic microbes
Detoxification
via proliferation of colonic microbes
Dietary Fibre
Some Properties-dictate physiological and metabolic
effects of fibre
d) Degradability or fermentability
Non-Fermentable fibres
Increased faecal bulk-good laxative effect
bulk consists of undigested fibre, salts and
water
-wheat bran and especially rice bran
particularly good at this