Carbohydrates Flashcards
(29 cards)
2 main types of carbohydrate
Starch and sugars (4kcal per gram)
Chemical symbol
C6H12O6
Monosaccharides
1 unit of sugar
- Simplest form
- Fructose, glucose, galactose
- Condensation to form disaccharides and polysaccharides
Disaccharides
2 units of sugar
- 2 monosaccharides through condensation with the water removed
- Joined through glycosidic bond
- Sucrose, maltose and lactose
Oligosaccharides
3-9 units of sugar - FOS and GOS
- Fructo-oligo saccharides - Small chains of fructose molecules
- Galacto-oligo saccharides - Small chains of galactose molecules (both 3-10 molecules in length)
- Provide food for colon gut bacteria
Polysaccharides
> 9 units of sugar
- Many monosaccharide molecules joined through condensation
- Includes starches and non-starch polysaccharides (NSP)
- Either straight chain (amylose) or branched (amylopectin)
Glucose
- Readily absorbed and metabolised
- Soluble in water
- Formed through hydrolysis of disaccharides and polysaccharides
Fructose
- Glucose + fructose = sucrose
- Same formula as glucose (different structure)
Galactose
- Glucose + galactose = lactose
- Same formula as glucose (different structure)
Starch
Principle carb in diet
- Digested through amylase
Amylose - Type of starch
- Straight chain of glucose
- Smaller and linear molecules with unbranched chains
- Main source of digestible starch
Less soluble in water and takes longer to digest
Amylopectin - Type of starch
- Branched chain of glucose molecules
- Larger and highly branched polymer
More soluble in water and faster digestion (higher on glycaemic index)
Resistant starch - Type of starch
- Resists digestion in small intestine due to glucose unit formations
Glycogen
- Highly branched polysaccharide (8-14 branches)
- Type of glucose
- Stored in small amounts in the liver and skeletal muscles
Where are carbohydrates digested
Along intestinal tract
Fibre (Non-Starch Polysaccharides – NSP)
- 2kcal/g
- Not digested or absorbed in small intestine
- Insoluble fibre - Adds bulk to stool and helps digestion - cellulose and hemicellulose
- Soluble fibre - Lowers cholesterol and helps digestion - pectin
Unrefined vs refined CHO
Unrefined - Brown and wholewheat versions, pulses, potatoes, nuts, legumes
Refined - White versions, sweets. chocolates, biscuits, crisps
Polyols
- Hydrogenated simple sugars (naturally occurring)
- Sugar replacements and sweeteners
- Doesn’t spike blood sugar
How are carbohydrates broken down
Through hydrolysis which occurs in intestinal tract
Digestion - mouth
Salivary amylase breaks down starches slightly
Digestion - stomach
Low pH inhibits salivary amylase
Digestion - small intestine (main site)
- Pancreatic juice neutralises gastric acid
- Polysaccharides > Disaccharides > Monosaccharides (breaks down by enzymes on brush border)
Digestion - colon
Resistant starches
- Oligosaccharides are fermented by gut bacteria
After absorption
Monosaccharides enter bloodstream through intestinal barrier
- If needed immediately, they pass into cells to be used as ATP
- If not, stored as glycogen until needed
