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Macronutrients - CARBOHYDRATES (Fibre (Benefits (Prevents constipation -…
Macronutrients - CARBOHYDRATES
Complex CHO
Polysaccharide - thousand of mono linked together
3 important ones polymers of D-glucose - starch, glycogen & dietary fibre
Broken down into simple sugars
Starch
Found in plant foods
Amylopectin - branched chains. 1-4 & 1-6
Amylose - unbranched 1-4
Glycogen
Formed within body tissues then converted as needed to glucose
Similar to amylopectin - shorter branches and more highly branched
Body store glucose as glycogen - branches attacked making surge of glucose available
Small amounts in meat by hydrolysed after slaughter
Not found in plants
Fibre
Fruits, vegs, legumes and grains
Can't be digested so vital for health
Indigestible Polysaccharides
Beta glycosidic bond
Cannot be broken into single sugar unit so does not raise blood glucose
Two types
Insoluble fibres - cellulose, many hemicellulose, lignin
Soluble fibres - gum, pectin, mucilage some hemicellulose.
Benefits
Prevents constipation - insoluble
Protects against colorectal cancer - insoluble
Preventing diverticulitis - insoluble
Reduce serum cholesterol - soluble
Weight management - insoluble
D-glucose exist as 2 forms - alpha and beta. Differ in direction of -H and -OH groups on carbon 1. Alpha = starch. Beta = Cellulose
Adult can store 500g/2000kcal of CHO. - 400g stored as muscle glycogen. 14-18g liver glycogen. 2-3 grams as blood glucose
Whole grains - inner layer of germ, middle layer endosperm and outer layer bran
When processed the germ and bran are removed and starchy endosperm is left
Whole grains higher in fibre, vitamins, minerals and beneficial compounds
Low GI - pulses, peas, bean legumes, oats, raw fruit, milk & plain yoghurt
Intermediate GI - new potatoes, granary bread, rice
High GI - bread, corn, wheat cereals, honey, fruit juice
Functions
Conserving protein during energy production
Quick source of energy - glucose
Normal function of intestines (fibre)
Laxative action - absorption of calcium - lactose
Energy supply to the cell - synthesis of ATP - fuel for the cell
Contribute to cellular structure and synthesis of cellular products
Form structure of DNA & RNA molecules
CHO should be kept as 47% - 50% total calories - maintain body weight and reduce risk of disease
The brain and the nervous system and blood only use CHO for fuel
High intensity exercise muscles use most energy from CHO
May be converted to non-carb fractions, such as glycoproteins to form structural components of the cell
Digestion
Begins in the mouth - food broken down into smaller particles
Chyme (food mass) moved into small intestines - most carb digestion occurs
Pancreatic amylase breaks down complex carb into disaccharides
Disaccharide enzymes (maltase, sucrase and lactase) breakdown into monosaccharides - only form body can form
Absorption
Monosaccharides - glucose, fructose and galactose absorbed through intestinal mucosa. Travel into the liver through portal vein. Small amounts of starch and fibre that not digested as excreted.
Soluble fibre slows the absorption of glucose - delays rise in serum glucose that occurs after eating.
Metabolism
Anabolism and catabolism keep carbs supply in constant flux