Carbohydrates Flashcards
What percentage of the energy in our diet does carb make up?
45-65% total calories
What are carbs made of?
Carbon
Hydrogen
Oxygen
How can simple carbs be classified?
Monosaccharide (one sugar)
Disaccharide (two sugars)
Oligosaccharide (more than 3, less than 10)
Polysaccharide (more than 10)
What are the 3 monosaccharides?
Glucose
Fructose
Galactose
What are the 3 disaccharides
Maltose
Sucrose
Lactose
What are the 3 complex carbs?
Starch
Glycogen
Fiber
What is glucose commonly known as?
Blood sugar
Essential energy source for all body’s activity
What is fructose?
Sweetest sugar
Occurs naturally in fruits
In desserts/soft drinks, etc
Does galactose naturally occur in foods?
No, rarely as a single sugar
How do disaccharides form?
Putting together two monosaccharides through condensation (water removed)
Hydrolysis (water added) will cause them to seperate again
What is maltose made of
2 glucose
Produced when starch breaks down (human digestion of carbs, fermenting alcohol)
what is sucrose?
One fructose, one glucose
Table sugar
What is lactose?
Galactose and glucose
Principle carb of milk/milk products
How much should complex carbs form your plate
50%, should be the majority of what you eat
What is glycogen?
Human body stores glucose unit as glycogen in highly branched chains
Arrangement permits rapid hydrolysis
Can only store 24hrs of it
Found in limited meats, not plants
How is glucose released?
When message to release energy arrives as glycogen storage sites (liver, muscles), enzymes respond by attacking branches to make surge of glucose avaliable
What is a starch?
Long chains of thousands of glucose molecules linked, stored in plant cells
Molecules packed side by side, body hydrolyses into glucose for energy
Wheat, grains, rice, tubers, root crops
What is the difference between an alpha and beta bond starch?
Alpha - easily digested (amylose)
Beta - are not broken down (amylopectin)
What is dietary fibre made of?
Non-starch polysaccharides - cannot be broken down by enzymes in body
What is the difference between soluble and insoluble fibre
Soluble - dissolves in water to forms a gel, lowers blood cholesterol, fermentable in colon, balances blood sugar levels, lowers risk of diabetes, satiety
Insoluble - fibres that do not dissolve in water, not very fermentable, adds bulk and soften stools, alleviates constipation and increases transit time
What are resistant starches and where are they found?
Starch that escapes digestion and can be fermented by bacteria to produce short chain fatty acids
- physically enclose (trapped) starch, found on coarse
- un-gelatinised (uncooked) starch (raw potatoes, green bananas)
- retrograded amylose (starch polymers) form after starchy foods have been cooked and left to cool
What is physic acid?
Found accompanying dietry fibre
Close bonds make it impossible to determine whether dietary fibre, physic acid or both that binds with minerals, preventing their absorption
Binding - risk of mineral deficiency, lessened if fibre/mineral intake is reasonable
What is the goal of carb digestion?
Breaking down sugars and starches into small molecules (chiefly glucose) for body to absorb and use
What happens in the mouth in carb digestion?
Salivary enzyme (amylase) hydrolysis starch to shorter polysaccharides
What happens in the stomach in digestion?
Stalled bolus mixes with stomach acid and enzymes, inactive salivary amylase
Dietary fibre lingers in stomach, delays gastric emptying (satiety)
Stomach acid doesn’t contain enzymes to digest carbs
What happens in the small intestine in carb digestion?
Major carb-digestive enzyme - pancreatic amylase - enters via pancreatic duct
Breaks down polysaccharides to shorter glucose chains and maltose
Goes to outer membranes of intestinal walls, where specific enzymes break down specific disaccharides
What enzymes does maltese, sucrose and lactase break down?
Maltese - Breaks maltose into two glucose molecules
Sucrose - breaks sucrose into one glucose and one fructose molecule
Lactase - breaks lactose into one glucose and one galactose molecule
What happens in the large intestine during carb digestion?
Dietary fibre remains in tract, attracting water, which softens stool for passge
Bacteria in GI tract also ferment some dietary fibre (forms water, gas, short-chain fatty acids)
Colon uses these fat molecules for energy
between 1-4 hours after meal, mostly digested
How are glucose and galactose absorbed?
Glucose and galactose - traverses cell linking of small intestine by active transport
Requires energy in form of ATP - transport protein is loaded with sodium, then glucose/galactose
How is fructose absorbed?
Absorbed by facilitated diffusion, which slows entry and produces smaller rise in blood glucose. It is ‘passive’ absorption
How are carbs digested?
Unbranched chains of starch are digested slowly, place for enzymes to attack and release glucose fast
As blood from intestines circulated to lover, cells there take fructose and galactose and convert them (often to glucose)
What is occurring in lactose intolerance?
Intestinal cells do not produce enough lactase (enzyme) to ensure disaccharides are digested and absorbed effectively
When more lactose is consumed than what lactase can handle, molecules remain undigested. Attracts water - causes abdominal discomfort and diarrhoea
Undigested lactose becomes food for intestinal bacteria, which multiplies and produces irritating acid and gas
What is the role of glucose in the body?
glucose is the main source of energy for the central nervous system
Plays central role in carb metabolism
How is glucose stored?
Stored as glycogen in liver, can release glucose into bloodstream when needed
Also stored in muscle cells - used mainly for exercise
Brain - emergency supply
What happens when blood glucose rises?
Liver cells link excess glucose molecules into long branching chains of glycogen
Happens after a meal
What happens when blood glucose falls?
Liver cells break glycogen by hydrolysis reactions into single molecules of glucose, releasing them into bloodstream
Why can glycogen only be stored for short periods of time?
Because it holds water, is therefore bulky and cannot be stored in excess
Long-term energy uses abundant, water-free fat
How is glucose broken down for energy?
Enzymes in cell breaks glucose down to carbon dioxide and water
What is gluconeogenesis?
When glycogen stores become depleted, the body makes glucose from protein
What is protein sparing?
The role of carbs - having an adequate amount of glucose in diet so protein can be stored
How are ketone bodies made?
If less glucose than required for brain’s energy, fat fragments combine
Ketone bodies provide alternative fuel source during starvation
When production exceeds their use, accumulates in blood (called ketosis, disturbing acid-base balance)
How does fat get made from glucose?
After meeting energy needs and filling glycogen stores, body stores the rest as fat
Liver forms glycerol (triglyceride)
Fat travels to fatty tissues for storage
How does the body maintain glucose homeostasis?
Homeostasis: body must maintain blood glucose within limits that permit cells to nourish themselves
If glucose falls - dizzy and weak
If glucose rises - fatigued
Regulated by two hormones from pancreas: insulin and glucagon
How does insulin work?
When blood glucose rises (after meal) pancreas respond by secreting insulin into blood
Insulin contacts receptors to move glucose from blood into cells, or conversion into fat
How does glucagon work?
When blood glucose falls, pancreas secrete glucagon into blood.
Signals to liver to break down glycogen stores to release glucose into blood
Why does adrenaline release glucose?
Adrenaline (fight or flight) signals liver to release glucose, to ensure body has energy to fuel emergencies
Why do complex carbs delay insulin response?
Carbs that digest slowly prolong the presence of foods in the digestive tract, providing greater satiety
What does epinephrine do?
Acts quickly to bring glucose out of storage during times of stress
What is diabetes?
When blood glucose surges after meal, remains above normal levels as insulin is either inadequate or ineffective
What is the difference between type 1 and type 2 diabetes?
type 1 - pancreas fail to produce insulin (genetic predisposition)
Type 2 - cells fail to respond to insulin (consequence of obesity)
What is hypoglycaemia?
When blood glucose falls below normal
Consequence of poorly managed diet - too much insulin, strenuous physical activity, inadequate food intake of illness
Results in weakness, anxiety, hunger, trembling
What is the glycemic response?
How quickly glucose is absorbed after a person eats, how high blood glucose rises and how quickly it returns to normal
Is a low or high glycaemic response required?
Low: slow absorption, modest rise, smooth return to normal
What is the glycemic index?
Classifying food according to their potential to raise blood glucose
Low GI foods also manage blood lipids to lower risk of heart disease
What is a low, medium and high GI?
Low <55
Medium 56-69
High 70>
What are some health effects caused by sugar?
- Obesity/chronic disease
- nutrient deficiencies (supplies energy without nutrients)
- dental caries/tooth decay
What are some alternative sweeteners?
Artificial sweeteners (no energy)
Herbal product (stevia)
Sugar alcohols (occurs naturally, bulk and sweetness)
How many kj (out of 8000) of calories should a person have a day?
3600-5200kj a day
200-325g (dietary fibre 25-30g)
What are the positive impacts of dietary fibre?
Fosters weight management
Lowers blood cholesterol
Enhances health of GI
Protects heart disease
Prevent colon cancer, diabetes, haemorrhoids, etc.
What occurs with excessive intake of dietary fibre?
Displaces energy and nutrient-dense foods
Causes intestinal discomfort and distension
May interfere with mineral absorption
