Fiber

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Fiber
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Dietary Fiber(s) is comprised of indigestible
carbohydrate polymers and lignin (phenolic
polymers) that, for the most part, come from the
cell walls of plants. Humans cant digest the
fiber because we dont have the enzymes to do so
(although some of the bacteria in our gut may).
Our enzymes either cant recognize the type of
carbohydrate in the polymer or cant hydrolyze
the bond. Example Cellulose is comprised of
glucose polymers where the glucose molecules are
joined by a ß-1,4 link as opposed to the a-1,4
link recognized by amylase. Functional Fiber(s)
is comprised of dietary fibers that have been
purified or synthesized or modified and added to
human foods. Functional fibers also have some
physiological benefits. Some
Some Dietary Fibers Functional
Fibers Cellulose Cellulose Hemicellulose Pe
ctin Pectin Lignin Lignin Gums Gums Ch
itin ß-glucans Chitosan
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Because some of the functions have definite
health-benefits, the IOM has established an AI
for total fiber g fiber Adult
Male 38 Adult Female 25 Really old
men (gt50) 31 Really old women (gt50) 21 and
somewhat lesser amounts for boys girls and
small children
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Function of the different fibers is dependent on
their water-soluble properties as well as their
ability to bind particular compounds and
digestibility by the bacteria in the gut. Water
Soluble Insoluble Some hemicelluloses Lignin P
ectin Cellulose Gums Some
hemicelluloses ß-glucans
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Some General Effects Soluble Fibers - Can
absorb some nutrients - bile acids fecal bile
acids - lipids lipid absorption serum
lipids - Can cause gel formation nutrient
absorption transit time digestive
function gastric emptying Some Soluble
Insoluble Fibers - Can bind water fecal
volume transit time frequency of defecation -
Can be fermented growth of beneficial bacteria
acid in colon bile acid
synthesis short-chain fatty acids lactate
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Some specific examples Lignins, gums, and
pectins absorb bile acids, fatty acids,
cholesterol - conversion of bile acids to
secondary bile acids by microflora may contribute
to carcinogenesis - decrease in lipid
absorption decreases serum levels and enhances
liver uptake of LDL Pectins, gums, some
hemicelluloses high water-binding -
increases fecal bulk and decreases transit time
- decreases transluminal concentration of
carcinogens / precarcinogens - decreases
time for production of toxins and
carcinogens Pectin, ß-glucans, gums
prebiotics that stimulate growth of helpful
bacteria - appears to inhibit initiation
proliferation of tumor cells - appears to
attenuate production of carcinogens -
appears to enhance production of butyric acid
which reduces proliferation and differentiation
of cancer cells Lignin can bind carcinogens to
enhance elimination through feces
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Major Dietary Sources Lignins seeds of fruits
vegetables, wheat bran, root vegetables
(carrots) Pectins strawberries, apples,
citrus fruits, some in legumes and
nuts Gums mostly as food additives with some
in oatmeal, barley, and legumes Hemicelluloses
bran, whole grains, nuts legumes ß-glucans cere
al bran Cellulose bran, legumes, nuts, root
vegetables, seeds, apple peels Obviously the
food groups that include whole grains, nuts,
seeds, and vegetables are the major sources of
fiber consumption of which is sadly lacking in
the average American diet!