Dietary fibers are classified as soluble or insoluble based on how they function in the body. Sources of soluble fiber include oats, fruits, vegetables, and nuts, while insoluble fiber sources are whole grains, legumes, and vegetables. Fibers promote health by bulking stool, increasing viscosity, and fermenting in the gut to feed beneficial bacteria and produce short-chain fatty acids. A diet high in fiber can reduce disease risk and support a healthy microbiome. Recommendations are 25-38 grams per day for adults depending on age, gender, and calorie needs.

1. Fiber

2. 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
5. Explain the impact of fiber on obesity and
weight reduction

3. 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.

5. 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

6. 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.

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

8. 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

9. 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 fermented in
the large intestine by gut
bacteria, producing short chain
fatty acids and gases.

10. Sources

11. 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 in
dietary fiber

12. Sources

13. 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
• the skins of some fruits, including
kiwifruit, grapes and tomato

14. Source

15. • 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.

16. • 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)
• Insoluble fiber- reduced risk of diabetes. Resistant starch, may increase insulin
sensitivity in healthy people.

17. • 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.

18. 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

20. 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)

21. • 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
7 g or more per day of soluble fiber from psyllium seed husk

22. Thank you