CHO Flashcards
Monosaccharides
Glucose
Fructose
Galactose
Condensation
A carbon on a monosaccharide bond with the oxygen of another –> release one molecule of H2O
Hydrolysis
The disaccharide bond breaks and require one molecule of water to complete the two monosaccharide
Oligosaccharides
3-10 monomeric units
i.e. Raffinose, Stachyose, Verbascose
Fructans (3-50 residues)
Raffinose, Stachyose, Verbascose
short-chain sugars of galactose, glucose & fructose.
- undigestable by endogenous enzymes - fermented by large intestine bacteria
Fructans
- fructose residues attached to single glucose
- insignificant gut hydrolysis
- fermented by large intestine bacteria
Polysaccharides
multiple sugar units
Starch (polymer of D-glucose)
- 2 forms amylose or amylopectin
- major carbohydrate in diet
- found in grains, vegetables, legumes
Glycogen
- Highly branched chains of glucose units
[ a 1-4 , a- 1-6 branching]
- Body’s storage form of carbohydrate
amylose & amylopectin
- Starch granules – semi-crystaline insoluble in water, retarding digestion.
- On heating with water semi-crystaline disrupted
- Random conformation readily assessable
- Cooling recrystalisation
Glucose + glucose
Maltose
α-1,4 glycosidic bond
Cellobiose
β-1,4 glycosidic bond
Glucose + fructose
Sucrose
α-1,5 glycosidic bond
Rapidly digestible starch (RDS)
- found in freshly cooked starch foods
- Rapid digestion
Slowly digestible starch (SDS)
- found in most raw cereals
- Slow digestion
Type of starch
Rapidly digestible starch (RDS)
Slowly digestible starch (SDS)
Resistant starch (RS)
- Physically inaccessible
- Resistant granules
- Retrograded amylose
Physically inaccessible resistant starch (RS)
in raw potato/banana
Resistant granules resistant starch (RS)
Cooked potato cooled
Retrograded amylose resistant starch (RS)
Bread, cornflakes
Resistant starch (RS)
Partly milled grain/seeds
Total Fiber =
Dietary Fiber + Functional Fiber
- Indigestible chains of monosaccharides
- Nonstarch polysaccharides: long chains
- Found in fruits, vegetables, grains, and legumes
Fiber types
[ i.e. cellulose, hemicellulose, pectins, gums, mucilages
Lignins, beta-Glucans, Chitin and Chitosan ]
CHO function in body
- Digestion and absorption
- Normal Use of Glucose
- Using Glucose for Energy
- Storing Glucose as Glycogen
- Sparing Body Protein
- Preventing Ketosis
Carbohydrate Digestion and Absorption
Mouth - Salivary amylase begins digestion of starch
Small intestine - Pancreatic amylase completes starch digestion / Brush border enzymes digest disaccharides
End products of carbohydrate digestion- Glucose, fructose, galactose –> Absorbed into bloodstream
Fibers are not digested- Fermented in gut or excreted in feaces
Pre-stomach Digestion
Salivary amylase : a 1-4 endoglycosidase
- to cleaves internal a1-4 glycosidic bond within a poly or oligosaccharide
Cannot attack a1-4 linkase close to 1-6 branch points.
Break into:
a Limit dextrins/ maltotriose/ maltose/ isomaltose
Stomach Digestion
- Not much carbohydrate digestion
- Acid and pepsin to unfold proteins
- Ruminants have four stomachs with extensive microbial populations to breakdown and anaerobically ferment feed
Small Intestine
has Pancreatic enzymes: a-amylase
cleave amylose –> maltotriose & maltose
cleave amylopectin –> maltotriose & maltose & a Limit dextrins
Break down of a- Limit dextrins involves enzymes:
[6] Glucoamylase (maltase) or a-dextrinase [twice] [4] --> a-dextrinase [3] --> maltase [2] --> sucrase [1 ]
Alpha dextinase
cleaves 1,6-alpha glucosidic linkages
Maltase
specifically removes a single glucose from the non- reducing end of a linear a1-4 glucose chain…breaking down maltose into glucose.
Starches break down to glucose
Starches [α-amylase] –> α-dextrins [α-dextrinase] + Maltose [Maltase] + Glucose
Sucrose break down to glucose
Sucrose [Invertase (Sucrase)] –> Fructose + Glucose
Lactose break down to glucose
Lactose [Lactase] –> Galactose + Glucose
Lactose intolerance
lack of lactase to hydrolysis lactose found in milk and break down in to glucose & galactose
75% adult population have lactose intolerance
Sugar transporters
- GLUT5 - Facilitative (passive) transporters
- GLUT2 - Facilitative (passive) transporters
[move sugars from high to low conc] - SGLT1 – Active transporters
- Na+/K+ -ATPase (work along with SGLT1)
Transportation of sugars in enterocytes
Ability to transport >10kg/day glucose, galactose and fructose
Rare genetic defects which prevents absorption of some sugars
GLUT5
Fructose from Gut into membrane
Facilitative (passive) transporters
[move sugars from high to low conc]
GLUT2
Fructose, glucose, galactose from gut cell into blood stream
Facilitative (passive) transporters
[move sugars from high to low conc]
SGLT1
Glucose, galactose, Na+ from gut lumen into gut cell
Active transporters
[required to move all glucose from low to high concentrations to ensure complete absorption from the intestine]
[Achieved by linking glucose transport to that pf sodium ie sodium moves down a strong concentration gradient carrying glucose with it up a concentration gradient]
High blood glucose
Insulin release:
- stimulate cells to take up glucose from blood
- stimulate liver and muscle to store glucose as glycogen
Low blood glucose
Glucagon release:
- stimulate liver to make glucose from amino acid
- stimulate liver to break down glycogen into glucose
Insulin action
- Uptake and utilisation of glucose in muscle
- Uptake and storage of glucose in liver and muscle
which involves glucose transporters (e.g Glut4 in adipose tissue) & glycogenesis - Induction of lipogenesis
- Protein uptake and biosynthesis in muscle
Glucagon action
- Glucagon released in response to falling plasma glucose
- Induces glycogenolysis - Break down glycogen from the liver into glucose
- Induces gluconeogenesis in the liver and kidneys, to produce glucose from non- CHO precursors
- Induce Lipolysis
Gluconeogenesis
produce glucose from non- CHO precursors
Protein breakdown in muscle & release of amino acids
Using amino acid as substrate: Glutamine and alanine
take up in liver and kidney for gluconeogenesis
Or
Lactate in Cori cycle
Or
Glycerol from Triglyceride breakdown
Glycogenolysis
Glycogen breakdown from Muscle & liver
CHO slide 38
Lipolysis
Breakdown of triglycerides in adipose tissue
Products:
~ Glycerol- glucogenic
~ Free fatty acids - not glucogenic, muscle fuel, ketone bodies
Hyperglyceamia
- Blood sugar >10 mmol/ l
- Common in diabetes
- Sugar toxicity - Diabetic coma
Hypoglycaemia
- Low blood sugar
- Brain has a requirement for glucose, but it can adapt to ketone bodies
Symptoms of short term sugar starvation
Tiredness / Confusion/ Irritability / Sweating
Diminishing Sugar Supply
Fatty acids - Main energy supply
Gluconeogenesis- Amino acids/ Lactate/ Glycogen
Ketogenesis- Liver/ Acetate/ Acetoacetate / hydroxybutyrate
NDNS Adults aged 19-64 years (2003)
Mean intake CHO
275g/day (47.7% eng) men
203g/day (48.5% eng) women
Cereals & cereal products (45% total CHO)
Potatoes & savoury snacks (12% total CHO)
COMA Nutritional Aspects Cardiovascular disease (1994)
Dietary eng derived from CHO increase to 55% total eng
Complex CHO and sugars in fruits & vegetables restore eng deficit in fat reduction.
COMA DRV (1991)
Non-milk extrinsic sugars 10% total eng
Intrinsic & milk sugars & starch 37% total eng
Total CHO 47% total energy
Glycaemic Index
Formula
the blood-glucose raising potential of CHO foods.
Incremental area under blood glucose response curve of 50g CHO portion of test food expressed as % of response of 50g CHO portion from standard food taken by same subject (white bread).
GI (%) = ( IAUC of glucose for test food / IAUC of glucose for reference food) X 100
Moderating extrinsic sugar intake
- Use less added sugar
- Limit soft drinks, sugary cereals, and candy
- Choose fresh fruits or those canned in water or juice
Strategies for Increasing Fiber Intake
- Grains, especially whole grains
- Legumes
- Vegetables
Nutritive Sweeteners
- Natural v. refined
- Sugar alcohols
Non-nutritive Sweeteners
- Saccharin
- Aspartame
- Acesulfame K
- Sucralose
- Other sweeteners
Sugar and Children’s Behavior
In a study designed to determine whether or not sugar truly affects a child’s behavior,
the results indicated that dietary sugar does not cause adverse behavior.
Dental Health
Good dental hygiene, adequate fluoride, and proper nutrition help maintain healthy teeth.
A well-balanced diet contains vitamins and minerals crucial for healthy bones and teeth.
Dental caries and sugar
Population where total sugar
COMA Panel recommendations on sugar
No evidence that intrinsic sugars or lactose in milk have adverse effects on health.
Extrinsic sugars (not lactose) predominantly sucrose contribute significantly to dental caries
Health benefits from apples.
Apples have a high pectin content, a soluble fiber known to be an effective GI regulator.
Dietary fiber
consists of non- digestible carbohydrates and lignin that are intact and intrinsic in plants.
Functional fiber
isolated, nondigestible carbohydrates that have beneficial physiological effects in humans.
Metabolic effects of dietary fiber
High fibre diet associated with
- Prevention of type 2 diabetes
- Decreased inflammatory status
- potential of cancer prevention
- increase energy density/ bulking effects or fulling /
- Regulate gut hormones
Soluble fibre:
- Decrease total & LDL cholesterol/ gastric emptying
Insoluble fibre:
- Increase insulin sensitivity / gut transit time
Type 1 Diabetes mellitus
Uncontrolled blood sugar
Auto immune disorder- Beta cells in pancreas are destroyed, Insulin production is knocked out
Often childhood onset
Management via insulin injections
Type 2 diabetes mellitus
Beta cells overworked
Insulin resistance - Chronic high exposure to insulin renders target cells unresponsive to its action
Associated with high sugar intake, central adiposity and sedentary lifestyles
