bichem

1. Dietary fibers- Objectives
1. Classify the dietary fibers and list their
sources
2. List their function and prevention of diseases
3. State the daily RDA and provide a
presciption
4. Explain the relationship of fiber to the
microbiome

2. 1. Classify the dietary fibers and list their sources
• Non-digestible form of carbohydrates
• Amount of dietary fiber varies based on the type of food.

4. Function and prevention of diseases
• Bulking fibers – absorb and hold water, promoting
regularity.
– Eg: cellulose and hemicellulose (including psyllium)
• Viscous fibers – thicken the fecal mass.
– Eg: beta-glucan and psyllium
• Fermentable fibers –feed the bacteria and
microbiota of the large intestine
– Eg: resistant starch, xanthan gum, and inulin

5. Function and prevention of diseases
Soluble fiber (fermentable fiber or prebiotic fiber)
– fermented in the colon into gases and physiologically
active by-products, such as short-chain fatty acids produced
in the colon by gut bacteria.
Examples are beta-glucans (in oats, barley, and
mushrooms) and raw guar gum
Psyllium
– a soluble, viscous, nonfermented fiber – is a bulking fiber
that retains water as it moves through the digestive system,
easing defecation.

6. • Soluble fiber
-viscous and delays gastric emptying
-feeling of fullness.
-lowers LDL
-Eg: beta-glucans from oats or barley

7. Insoluble fiber:
• does not dissolve in water
• is inert to digestive enzymes in the upper gastrointestinal
tract.
• Examples are wheat bran, cellulose, and lignin.
• Coarsely ground insoluble fiber -providing bulking.
• Some forms of insoluble fiber, such as resistant starches,
can be fermented in the colon

8. British Nutrition Foundation- DF
• Dietary fibre refers to a
group of substances in
plant foods which cannot
be completely broken
down by human digestive
enzymes.
• This includes waxes, lignin
and polysaccharides such
as cellulose and pectin.
• Some fibre can be

9. Sources

10. Sources of Soluble fiber:
• legumes (peas, soybeans, lupins and
other beans)
• oats, rye, chia, and barley
• some fruits (including figs, avocados,
plums, prunes, berries, ripe bananas,
and the skin of apples, quinces and
pears)
• certain vegetables such as broccoli,
carrots, and Jerusalem artichokes
• root tubers and root vegetables such
as sweet potatoes and onions (skins
of these are sources of insoluble fiber
also)
• psyllium seed husks (a mucilage
soluble fiber) and flax seeds
• nuts, with almonds being the highest

11. Sources

12. Sources insoluble fiber
whole grain foods
• wheat and corn bran
• legumes such as beans and
peas
• nuts and seeds
• potato skins
• lignans
• vegetables such as green
beans, cauliflower, zucchini
(courgette), celery, and nopal
• some fruits including avocado,
and unripe bananas

13. Source

14. • Humans lack the necessary enzymes to split the
glycosidic bond and they reach the large intestine. Many
foods contain varying types of dietary fibers, all of which
contribute to health in different ways.
• Dietary fibers make three primary contributions: bulking,
viscosity and fermentation.
• cellulose and wheat bran - bulking effects; minimally
fermented.
• psyllium - bulking + viscosity.

15. • Bulking fibers can be soluble (e.g. psyllium) or insoluble (e.g.
cellulose and hemicellulose).
• They absorb water and can significantly increase stool weight
and regularity.
• Viscous fibers thicken the contents of the intestinal tract-->
reduce sugar response after eating, and reduce lipid absorption.
Their use in food formulations is often limited to low levels, due
to their viscosity and thickening effects. Some viscous fibers
may also be partially or fully fermented within the intestinal tract
(guar gum, beta-glucan, glucomannan and pectins), but some
viscous fibers are minimally or not fermented (modified
cellulose such as methylcellulose and psyllium)

16. • Fermentable fibers are consumed by the microbiota within
the large intestines, mildly increasing fecal bulk and
producing short-chain fatty acids as byproducts with wide-
ranging physiological activities.
• This fermentation influences the expression of many
genes within the large intestine, which affect digestive
function and lipid and glucose metabolism, as well as the
immune system, inflammation and more.

17. Microbiome
• bacterial fermentation
of some dietary fibers
• thereby an increase in
bacterial mass
• an increase in bacterial
enzyme activity
• changes in the water-
holding capacity of the
fiber residue after
fermentation

19. Dietary Recommedations:
• European Food Safety Authority
–dietary fibre intakes of 25 g per day -Normal laxation in
adults
• United States Academy of Nutrition and
Dietetics
–Adult men (Age 19 to 50)- 38g DF/day (age>50, 30g)
–Adult Women (Age 19 to 50)- 25g DF/day (age>50,
21g)

20. – United States Academy of Nutrition and Dietetics
Median of 14 g DF/ 1,000 Calories- lowest risk of coronary
heart disease
• The United States FDA
1.7 g per serving of psyllium husk soluble fiber or
0.75 g of oat or barley soluble fiber as beta-glucans to
claim that regular consumption- reduce the risk of heart
disease
3 g or more per day of beta-glucan soluble fiber from
either whole oats or barley, or a combination of whole oats
and barley