Dietary Fibre

Question 1

What is functional fiber?

Answer 1

•Non-digestible carbohydrates that have been isolated, extracted and manufactured are known as “functional fiber”

Question 2

What is fiber?

Answer 2

•Non-digestible carbohydrates and lignin that are intrinsic & intact in plants

Question 3

What is the recomended intake of fiber? How much do we actually consume? How can we get enough?

Answer 3

Adequate intake of fiber is 14g per 1000kcal of energy consumed or 38g per day for men and **25g per day for women **

Average actual consumption is 17g/day for men and 13g/day for women –> this is too low

Adequate daily dietary fiber intake can be achieved by eating fiber rich legumes as the main protein source, a minimum of 5 servings of fruits & vegetables and a minimum of 2-3 servings of whole grain.

Question 4

What are the classifications for Fiber?

Answer 4

1. Chemical classification
2. a) Classification based on solubility b) Classification based on water-holding capacity
3. Classification based on Fermentability

Question 5

What are the main types of fiber?

Answer 5

•Major botanical categories of fiber are:
**–Cellulose
–Hemicellulose
–Pectin
–Gums
–Mucilage
–Lignin **

Question 6

What are the properties and classifications of Cellulose?

Answer 6

• Most abundant and found in plant cell wall
• striaght chain of β 1-4 linked glucose units
• water insoluble
• poorly digestible by colon bacteria
• some cellulose is fermentable but mostly it is **unfermentable **

Question 7

What are the properties and classifications of Hemicellulose?

Answer 7

• Made of heterogenous polysaccharide units
• made of sugars like xylose, mannose, galactose (main chain) and arabinose, glucuronic and arabinose (side chain)
• Fermentability of hemicellulose is affected by type of sugars and their position –> some hemicellulose is fermentable
• some hemicellulose is water soluble and some insoluble

Question 8

What are the properties and classifications of Pectin?

Answer 8

• made of polysaccharides known as galacturonoglycans
• Galacturonic acid is the main constituent of pectin
• It is water soluble, gel forming and stable at low pH
• highly fermentable in the colon
• comercial pectin added to foods
• source of pectins are apples, citrus fruits, strawberries, and legumes

Question 9

What are the properties and classifications of Gums?

Answer 9

• Gums are secreted by plants in response to an injury (ex: arabic gum) and also produced from some seeds (ex: guar gum)
• gums are water soluble
• gums are highly fermentable in the colon

Question 10

What are the propeties and classifications of Mucilage?

Answer 10

• mucilage is a glycoprotein made by most plants
• rich sources include cactus, flaxseed, and okra
• Mucilage is not water soluble
• Mucilage is highly fermentable by microflora in the colon

Question 11

What are the properties and classification of Lignin?

Answer 11

• phenolic compounds associated with the cell wall
• water insoluble
• highly indigestible (unfermentable) by colonic microflora
• mature root veggies are a good source of lignin
• greatly affects the fermentation of other cell components

Question 12

What are some other dietary fibers?

Answer 12

1. β-glucans (found in oats)
2. Fructans, oligofructose, fructooligosaccharides
3. Resistant starch (ex: starch in cell wall)
4. Psyllium (psyllium seeds) –> high water holding capacity (viscous)

Question 13

What are the fibers that are insoluble?

Answer 13

1. Cellulose
2. Lignin
3. Mucillage
4. Some Hemicellulose

Question 14

What are the fibers that are soluble?

Answer 14

1. Pectins
2. Gums
3. ß-glucans
4. some hemicellulose

Question 15

Soluble fiber has a ______ Water holding capacity than insoluble fiber.

Answer 15

Soluble fiber has a HIGHER water holding capacity than insoluble fiber. Insoluble fiber does not absorb water.

Question 16

Some water soluble fibers that form viscous gel in the G.I tract are… ?

Answer 16

Psyllium and Pectin (also ß-glucans)

Viscous gel–> traps enzymes –> less interactions

if animal feed has lots of dietary fiber, then the animal will have less meat on it and the producers will lose money.

Question 17

What are the effects of viscous gel on the G.I tract??

Answer 17

1. delays gastric emptying. fiber forms gel like substance in your stomach and you feel full (ex: PG-X weight loss)
2. Produces a physical barrier that may reduce interactions between enzymes and nutrients
3. Reduces enzyme function (trapped in gel therefore cannot interact as much)
4. Decreases nutrient absorption (ex:glucose + fatty acids) by thickening the unstired water layer of the glycocalyx

Question 18

What are the effects of delayed nutrient absorption? (caused by the viscous gel)

Answer 18

1. Delayed absorption of glucose results in less glucose in your blood and therefore less insulin is released
2. The more viscous the fiber, the less absorption of glucose and the greater the effect in lowering the blood glucose level. High blood glucose concentration promotes cholesterol biosynthesis
3. Fiber may reduce plasma cholesterol level via its effect on glucose tolerance (lowering of blood glucose levels)
4. reduces lipid absorption by absorbing fatty acids, cholesterol and bile acids and interferring with micelle formations ( soluble fibers –>pectin, B-glucans, gums and insoluble fibers –>lignin)

Question 19

What are the hypercholesterolemic properties of dietary fiber?

Answer 19

• Dietary fiber reduces levels of glucose in blood
• interfers with micelle formation –> less micelles and less cholesterol, bile acids, in blood system
• Lipid compounds adsorb to dietary fiber are not absorbed and will be excreted or degraded by colonic bacteria
• Fiber binds to bile acids causing them to not be reabsorbed, and they are excreted in feces or degraded by colonic bacteria
• fiber prevents the formation of more cholesterol and therefore more bile acids like cholic acid

Question 20

What are some fermentable fibers?

Answer 20

Pectin, Gums, Mucilage, some hemicellulose, some cellulose

Question 21

What are the products of fermented fiber??

Answer 21

1. short chain fatty acids ( propionic, acetic, & butyric)
2. Lactic acid
3. gases such as CO₂, CH_4,H₂

Question 22

What are some examples of nonfermentable fiber?

Answer 22

Cellulose & lignin

Question 23

What are the benefits of short chain fatty acids?

Answer 23

1. Stimulates water & Na absorption (in the glycocalyx)
2. Stimulates mucosal cell proliferation (butyrate is the preferred energy source for colonocytes)
3. Provision of energy (mainly propionate & acetate)
4. Propionate inhibits 3-hydroxy-3-methylglutaryl CoA reductase (key enzyme in cholesterol synthesis)
5. Acidification of luminal environment and affects bacterial reactions in the colon. Ex. Bacteria forming secondary bile acids from primary bile acids

Question 24

What are the benefits of Nonfermentable fiber?

Answer 24

1. Stimulates proliferation of microbes in the colon who have a detoxification role as:

• Scavengers
• Inhibit tumor growth
• Inhibit conversion of procarcinogens into carcinogens (Lignin side chains)

2. Increases fecal volume:

• Fecal bulk increases as fermentability of dietary fiber decreases (unfermentable fiber are still in colon –> not broken down fecal bulk increased)
• Other effects of slowly fermentable fibers include higher frequency of defecation, reduced intestinal transit time and decreased intra-luminal pressure

Question 25

How might dietary fiber prevent colon cancer??

Answer 25

Dietary fiber may prevent colon cancer by :

• absorbing bile acids and therefore reducing the concentration of free bile acids (free bile acids are converted to secondary bile acids which promote colon carcinogenesis)
• Short chain fatty acids reduce luminal pH and therefore decrease synthesis of secondary bile acids
• Fibers increase fecal bulk and therefore reduce interaction of carcinogens with colonic mucosa
• Butyric acid reduces proliferation of cancer cells
• Insoluble fibers bind carcinogens (Lignin)
• Fermentable fibers provide substrates (SCFA) for normal colonocyte metabolism