2. Sources of Carbohydrates
Dietary sources rich in Carbohydrate: table sugar,grains, tubers
Dietary sources low in Carbohydrate: meat and egg
Dietary available carbohydrates (metabolised /utilised /can be
digested and assimilated to give energy): glucose , fructose ,
lactose , maltose ,sucrose, starch and sugars
Carbohydrate may provide about 60-65% of total calories (chief
source of energy).
Dietary unavailable carbohydrates (not utilised/cannot be
digested , assimilated and constitute only as the dietary fibre):
cellulose, hemicellulose, pectins,gum
3. Dietary Sources of carbohydrates
Carbohydrate Source Average daily intake(g) Relative sweetness
Sucrose Cane sugar 50-100 100
Lactose Milk 10-15 30
Maltose Malt Traces
Fructose Fruit,honey 2.5 170
Glucose Fruit,honey 2-5 50
Starch
Cereals,
pulses, and
tubers
200-300 0
Glycogen Meat Traces 0
Dextrin
Along with
starch
Traces 0
5. Starch as a source of energy
Digestion of Starch:
Starch Maltose Glucose (enzymatic hydrolysis of starch)
Function of Glucose : the major source of fuel for most organs and tissues ,
excess converted to fat and stored.
Properties of starch : bland taste, more soluble , accessible for digestible
enzymes, slow digestion and absorption ,satiety value .
On cooking Starch is made more soluble and accessible to digestive enzymes.
Major Dietary sources of starch : cereals ,pulses, tubers ,Germinating seeds
Partial breaking of starch from germinating seeds increases Serotonin
(calming chemical in brain).
Amylase Maltase
6. Dietary sources of sucrose : cane sugar,Jaggery (good source of Iron)
Sucrose Glucose + Fructose
Function of Glucose : major source of energy, excess converted to fat
and stored.
Adverse effects of Excessive sucrose intake: large quantity of refined
sugar (sucrose)increases blood sugar and plasma lipids (aggravate
many associated health complications).Therefore, Diabetic patients
should avoid sucrose(table sugar) intake.
Sucrose is sweetening agent excessive intake fermented by
bacteria damage enamel dental caries (tooth decay)
Sucrose as a source of energy
sucrase
7. Requirement of Carbohydrate food sources for vegetarians
and non vegetarians
Food source
quantity /requirement for
vegetarians
quantity /requirement for
non-vegetarians
Cereals 350g 350g
Pulses 75 g 60g
Vegetable oil 40 ml 25ml
Milk 250 ml 150ml
Leafy
vegetables
200g 200g
Sugar 25g 25g
Fish /meat none 60g
8. Sources of Dietary fibres in Nutrition
• Dietary fibres are complex carbohydrates that are not digested by
human enzymes .They are unavailable or indigestible carbohydrates
in diet.
• Soluble fibres : dissolve in water and form gels. e.g. Pectins , gums ,
Mucilage . Pectins and gums are digestible by bacterial enzymes.
• Sources of soluble Dietary fibres: fruits and legumes
• Insoluble fibres : adsorb water and swell up. e.g. Cellulose,
Hemicellulose, Lignin
• Dietary Sources of insoluble Dietary fibres: fresh fruits ,leafy
vegetables, whole wheat/grains , rice bran and grains
• Recommended daily intake of dietary fibres / indigestible
carbohydrates to reduce intake of refined carbohydrates : 30g
9. Biochemical nature of dietary fibres
Dietary fibre Chemical constituents Functions of dietary fibre
Cellulose polymer of Glucose
retains water in faeces , promotes
peristaltic action, increases bowel
action
Hemi-cellulose
pentoses ,hexoses ,
uronic acid
retains water in faeces,increase bile
acid excretion
Ugnin aromatic alcohols
Antioxidant , increase bile acid
excretion , decrease serum
cholesterol levels
Pectin
Partially esterified
rhamnogalacturonan
absorbs water ,slows gastric
emptying ,binds bile acids,
increases their excretion
Mucilage
branched Arabinose
glycan
binds bile acids thereby decrease
serum cholesterol levels, improve
glucose tolerance
Lignin Aromatic alcohols
Antioxidant , increase bile acid
excretion
10. Activity of dietary fibres along the entire gastro-intestinal tract
Stool after inclusion of dietary fibres in food : softens ,bulky
site of GI tract Activity of dietary fibre
Mouth stimulates saliva secretion
Stomach Delays gastric emetempting
Small intestine Delays absorption
Large intestine Traps water , binds cations
11. Importance of dietary fibres in Nutrition
• Importance of dietary fibres:
1. increase bowel mobility of gastrointestinal tract therefore prevents
constipation by absorbing 10 times its own weight water.
2. elimination of bacterial toxins : fibres adsorbs water detoxify toxic
compounds produced by intestinal bacteria increase fecal mass easy
expulsion(prevent haemorrhoids and diverticulosis)
3. decrease gastrointestinal cancer : Lower incidences of colon and rectum
cancers in vegetarians compared to non-vegeterians.
4. improve Glucose tolerance : by decreasing glucose absorption from
intestine (hypoglycaemia).
5. reduce plasma cholesterol level :by reducing absorption of dietary
cholesterol from intestine (hypolipidemic) . Fibres bind with bile salts and
reduce their enterohepatic circulation. Thus, there is elevation in
degradation of cholesterol to bile salt and its disposal from the human body
as bile salts .
6. Satiety value : Dietary fibres absorb water thereby increase weight of
ingested foodstuff and give a sensation of stomach fullness giving satiety
without consumption of excess calories (helpful weight reduction).
12. Adverse effects of dietary fibres in Nutrition
The harmful effects of dietary fibres are observed in people
consuming their large quantities .
Adverse effects of dietary fibres in nutrition include :
• Decrease digestion and absorption of proteins
• Decrease intestinal absorption of certain minerals
(e.g.Calcium ,Magnesium, Phosphorous)
• Fibres increase flatulence (anaerobic oxidation of carbohydrates
by intestinal bacteria produce gases such as sulphur
dioxide ,methane)and often cause discomfort.
Drinking plenty of water along with fibres is advocated to reduce
adverse effects of fibres.
13. Nutritional importance of carbohydrates:1
• Major source of energy : 60-80% of energy /metabolic need of
human body fulfilled by carbohydrates.
• Protein sparing effect : Proteins performed specialised functions of
body building and growth. carbohydrates come to rescue and spare
proteins from being misused for calorie purpose. The wasteful
expenditure of proteins to meet energy needs should be curtailed.
• Absolute requirement of brain : brain and other parts of central
nervous system are dependent on Glucose for energy .Prolonged
hypoglycemia may lead to irreversible brain damage.
• Required for oxidation of fat : “FAT BURNS IN A FUAL OF CARBOHYDRATE”.
TCA Acetyl CoA + Oxaloacetate Citrate
Excess fat utilisation leads to deficiency of carbohydrate and ketosis.
from carbohydrate metabolism
from fatty acid oxidation
14. Nutritional importance of carbohydrates:2
• Energy supply for muscle work:
Glycogen Lactic acid
• Synthesis of pentoses:Ribose is constituents of nucleic acids,coenzymes.
Ribose Nucleic acids (DNA /RNA) , Coenzymes ( NAD
+
,FAD)
• Synthesis of non -essential amino acids using intermediate of carbohydrate
metabolism:
e.g. Pyruvic acid Alanine Oxaloacetic acid Aspartic acid
• Synthesis of fats / lipids :
Excess consumption carbohydrate formation of lipids (e.g.Triacylglycerol )
stored in the adipose tissue
• Integration of metabolism in Liver: carbohydrate integrate all metabolisms
• Importance of non-digestible carbohydrates : not utilised by body but they improve
bowel motility , lower cholesterol ,prevent constipation , improve glucose tolerance
energy
muscle contraction
15. High fructose corn syrup(HFCS)
• Production of HFCS: from glucose by employing enzymatic
process that convert glucose into fructose.
• Composition of HFCS: equal amount Glucose and Fructose.
• Metabolism & composition of HFCS:similar to sucrose(except
HFCS is injected as a mixture of monosaccharides).
• Post-prandial glucose and insulin response of HFCS: not
significantly different from sucrose.
• Application of HFCS:substitutes for sucrose in beverages ,soft
drinks and processed food items.
16. • There are variations in the increase and fall of blood glucose
levels after ingestion of different carbohydrates containing
food items.
• These quantitative differences are assayed by glycemic index.
• Glycemic index measures the time course of post-pandrial
glucose concentration from a graph(glucose tolerance curve/
glycemic response).
• Definition of Glycemic index: as the area under blood glucose
curve after ingestion of a food item compared with the area
under blood glucose curve after ingestion of same amount of
a reference carbohydrate such as glucose . It is expressed as
percentage .
Glycemic index
17. Glycemic Index curve
Plasmaglucosemg/dL
Meal
I I
Reference meal(glucose)
Test meal
1 2
Hours
Glycemic Index is lowered when dietary carbohydrates are
mixed with protein / lipid / fibres.
Glycemic
index=
Schematic diagram
area under glucose tolerance curve after 50 g test meal x100
area under glucose tolerance curve after 50 g reference meal
18. High and low Glycemic Index
Glycemic Index : is assessed by Glucose tolerance test (Glycemic response) after
dietary intake of 50g test meal(always glucose) comparing it with a reference meal.
High Glycemic index : simple carbohydrates Glucose ,cane sugar(refined sugar)
Low Glycemic index :complex carbohydrates i.e.starch (as slow digestion and
absorption of complex carbohydrates therefore they will not increase in blood
sugar levels to the same extent).
Glycemic Index is lowered when carbohydrate is combined with protein ,fat and
fibre (preferably at least two of the three) in the diet.
Ice cream contains sugar but it has relatively lower glycemic index (as its high
fat content lowers glucose absorption).
incremental area under Glucose tolerance curve after 50 g of reference meal(Glucose)
incremental area under Glucose tolerance curve after intake of 50 g of test mealGlycemic
Index=
X100
19. Glycemic Index of carbohydrate rich food items
Food with high fibre content and low glycemic index should be preferred
for consumption.
food item Glycemic Index
Glucose 100
Carrots 90-95
potato chips/Honey 80-90
Bread/White rice (polished ) 70-80
Parboiled rice(brown) 60-69
Bananas/potato 60-69
Sweet potato 50-60
Beans/peas 40-49
Oranges /apples 40-45
Legumes /peanuts 35-40
ice cream/milk 35-40
Fructose 20-25
soya bean 15-20
20. Nutritional importance of Glycemic index
• Nutritional importance of a Glycemic index is controversial.
• This is due the fact the food with low glycemic index need not be good
for health.
• Food with low glycemic index usually have higher satiety value
(creating sense of stomach fulness) and thus may be helpful in limiting
the calorie intake.
• Food with high fibre content and low glycemic index (e.g. vegetables,
whole grains ,fruits) should be preferred for consumption.
21. Diet for patients with Diabetes Mellitus :1
• avoid sugar ,sweets and refined carbohydrates
• increase intake of green leafy vegetables
• increase intake of fibre content
• restrict intake of tubers
• fixed quantity of fat intake(30% of total kcal as fat)
• increase intake of Polyunsaturated Fatty acids(30% of fat
intake)
• reduce dietary intake of cholesterol rich food
• frequent small meals with distribution of calories intake
22. Diet for patients with Diabetes Mellitus :1
• avoid sugar ,sweets and refined carbohydrates
• increase intake of green leafy vegetables
• increase intake of fibre content
• restrict intake of tubers
• fixed quantity of fat intake(30% of total kcal as fat)
• increase intake of Polyunsaturated Fatty acids(30% of fat
intake)
• reduce dietary intake of cholesterol rich food
• frequent small meals with distribution of calories intake
23. Diet for patients with Diabetes Mellitus:2
• Management of diabetes : dietary control and exercise
to keep blood glucose levels near the normal values,
for as many hours as possible in a day.
• Post-pandrial hyperglycaemia is reduced by :
1. Giving diet with low glycemic index, so that elevation
glucose is minimal.
2. Giving the total calories in small divided doses so
that small quantity of food to be taken at frequent
intervals (2hrs) between 6am and 8pm.
24. Small meals with distribution of calorie intake for Diabetic patients
The calorie requirement of diabetic patients is distributed into proximate
principles i.e.carbohydrate(60-70%): fat(15-25%): proteins( 15-20%).
Small meal % calorie intake
Midmorning(snack) 5
Bedtime snack 5
Evening tea 10
Breakfast 15
Lunch 30
Dinner 35