Macronutrients

1. MACRONUTRIENTS

3. Fibre Occurrence Chemical Nature Source
Insoluble fibre Cell wall
constituents
• Polysaccharide
• ꞵ-glucose
• 1-4 linkage
• Amylase
Whole wheat flour,
Bran, Root, Vegetables,
Legume, Peas, Outer
covering of seeds, Apples
Cellulose
Hemicellulose Secretions,
Cell wall
material
• Polysaccharide
• Pentose, Hexoses, Uronic acid
• Hydrolysis: dilute acids,
digestive juices
• Fermentability by intestinal
micro flora is influenced by
structure and type of sugar
Bran
Whole grains
Lignin Woody parts of
plants
• Part of plant cell wall and
contributes to the structural
rigidity of plants
• Function: Resistance of cell
wall to microbial degradation
• Insoluble in water
• Not digested by colonic bacteria
Mature root vegetables such
as carrot,
fruits with edible seeds,
strawberries
COMPONENTS OF DIETARY FIBRES

4. Fibre Occurrence Chemical Nature Source
Soluble fibres Intracellular
cementing
material
• Galacturonic acids – anhydro
galacturonide residues
• Hydrolysis: Galacturonic acid
+ Galactose + Arabinose
• Water soluble
• Gel: In presence of sucrose and
citric acid
• Completely metabolised by
colonic bacteria
Apple,
Guavas,
Citrus fruits,
Carrots,
Strawberries
Pectins
Gums Secreted at the
cite of plant
injury by
specialised
secretory cells
and can be
exuded from
the plants
• Sugar and sugar derivatives
• Galactose, glucuronic acid and
uronic acid
• Highly fermented by colonic
bacteria
Gum Arabic,
Oatmeal,
Barley,
Legumes
COMPONENTS OF DIETARY FIBRES

5. SOURCES OF DIETARY FIBRE
Soluble dietary fibre: Green leafy vegetables (100g/day) and majority of fresh fruits (30%)
Grain: Whole grains and bran
Pericarp (Insoluble fibre) and aleurone layer (insoluble and soluble fibre)
Low amount of dietary fibre: Refined and processed foods
No dietary fibre: Sugar, Oil, Milk and Meat
Soluble dietary fibre: Mango, orange, papaya, sweet lime (rich source)
THERE IS NO
EFFECT OF
COOKING ON
DIETARY FIBRE
CONTENT

6. PROPERTIES OF DIETARY FIBRE
1. Water-holding capacity and viscosity:
Depends on pH of GIT, solubility, size of the fibre particles and degree of processing foods
Pectins, gums and hemicelluloses – high water-holding capacity
Delayed gastric emptying:
Viscous gel or hydrate form
Release of chyme from stomach is delayed
Nutrients remain in the stomach longer
Slows down digestion process
Post prandial satiety
Reduced mixing:
Presence of viscous gels in the GIT can impair the ability of the nutrients in the food to interact
with the digestive enzymes

7. PROPERTIES OF DIETARY FIBRE
Reduced enzyme function:
Viscous gel-forming fibers interfere with enzymatic hydrolysis
Hydrocolloids may inhibit intestinal peptidases and pancreatic lipase.
Fibre directly may decrease the activity of these enzymes or act by reducing the rate
of enzyme penetration into the food.
Decreased nutrient diffusion rate:
Absorption of nutrients: Lumen of the small intestine through glycoprotein
(mucin) rich water layer lying on top of the enterocytes
The hydrated gel increases the thickness of the water layer and decreases the
diffusion rate of nutrients; consequently, maximal absorption is reduced.

8. PROPERTIES OF DIETARY FIBRE
Altered small intestine transit time:
Soluble fibres with decreased diffusion rates, with increased transit time may result
in decreased nutrient absorption.
This is due to insufficient time for the nutrients to be in contact with enterocytes.
Soluble fibres with the viscosity increasing property slow down passage and
delay gastric emptying.
A high intake of dietary fibre generally causes reduced transit time in the colon
and faster bowel emptying.
This is attributed to accelerated colonic mobility by increased intraluminal mass.
Higher the faecal bulk, lower will be the transit time in the large intestine.

9. ADSORPTION OR BINDING CAPACITY
Lignins, gums, pectins and hemicelluloses have the ability to bind substances such as
enzymes and nutrients in the gastrointestinal tract.
The ability of these fibres to adsorb substances depends in part on gastrointestinal pH,
particle size, food processing and fermentability.
Mucilaginous fibres such as guargum, pectin and psyllium delay glucose absorption,
lower blood glucose concentration and affect hormonal response to the absorbed nutrient.
Such effects reduce post prandial blood glucose concentration and insulin needs and
beneficial for diabetic patients.

10. DIMINISHED ABSORPTION OF LIPIDS
Soluble and insoluble fibres may affect lipid absorption by adsorbing fatty acids,
cholesterol and/or bile acids within the digestive tract.
Fatty acids and cholesterol that are bound to fibre cannot form micelles and
cannot be absorbed in this bound form.
 Fibre bound lipids are typically not absorbed in the small intestine and pass into
the large intestine, where they will be excreted in the faeces or degraded by intestinal
bacteria.

11. INCREASED FAECAL BILE ACID
EXCRETION
Adsorption of bile acids to fibres prevents the use of bile acids for micelle formation.
Like fibre bound fatty acids, bile acids bound to fibre cannot be reabsorbed and recirculated
and excreted or undergo colonic microflora degradation.

12. LOWERED SERUM CHOLESTEROL
CONCENTRATION
Psyllium, guar gum, oat and pectin lower serum cholesterol.
Oat bran and soyabean fibres have intermediate effects.
Corn, wheat and rice bran appear to be ineffective.
Fruits and vegetables decrease serum cholesterol concentration.