13 - Carbohydrates Flashcards
Carbohydrates make up … of energy in NZ diets
40-60%
… is the primary metabolic fuel in humans is stored as . in … and …
Glucose is the primary metabolic fuel in humans and is stored as glycogen in liver and muscle
… … is highly regulated. It’s regulation is dependent on … and ….
blood sugar. its regulation is dependent on nutrition and hormonal status
3 key function of carbohydrates?
- Supplies energy
- Is protein sparing (if there is enough carbohydrates then we don’t break down lean body tissue)
- Prevents ketosis - in abscence of glucose we start . to utilise fats, lean body mass and eventually our own fat and become ketotic
Carbohydrates are … …, …. and … intermediates
Fuels, energy stores and metabolic intermediates
… and … …. are part of the structural framework of DNA/RNA
Ribose and deoxyribose sugars
…. makes up plant cell walls
cellulose
Carbs are often linked to … and ….
proteins and lipids
… … is used in blood glucose regulation especially in …
Glycaemix index is used in blood glucose regulation especially in insulin dependent diabetes
Staple foods
For centuries/thousands of years foods that contain carbs have been used as staple foods in most cultures and ethnicities
Examples of staple foods
asian - rice
european - wheat and potatoes
pacific - casava
native american - corn/maize
Once digested ALL carbs become … the … … …
glucose - the metabolically active unit
Starches are
long chain lengths of glucose (Plant version of glycogen)
Fibre is
The part of the carb we can’t digest that the bacteria in our large bowel ferment
Examples of sources of insol and soluble fibre?
Insoluble - bran or branflakes
soluble .- lentils, beans, oatmeal
Carbohydrates consist of … and …
ketones and aldehydes
What are the smallest possible units of sugar and give examples
monosaccharides - fructose (fruit), glucose (major source of E for a cell) galactose (dairy)
Disaccharides
Two mono joined via dehydration reaction
All have glucose backbone
lactose - galactose and glucose (natural sugar. Makes up all the carbs in milk)
maltose - glucose and fructose (fermentation of alcohol and browning reaction)
sucrose (table sugar and processed foods) - glucose and glucose
What are carbs
Long units of glucose
Oligosaccharides are … glucose units long
3-10
Polysachharides are .. units long
Chains of 2 or more monosaccharides
Starches are
The storage form of glucose/polysaccharides in plants. Starches are glucose polymers made up of amylose (not branched) and amylopectin (branched) - NOT water soluble
What is the most branched glucose polymer?
glycogen in order to pack into cells
How does cooking affect structure of starches?
structure changes - bonds break and so they become softer i.e. potatoes
What is another name for dietary fibre?
Non-starch polysaccharides
Non-starch polysaccharides?
dietary fibre - like polysaccharides but their glucose links can’t be broken by enzymes so they are not digested and contributes NO monosaccharides and little energy
Soluble fibre?
Dissolves in water, forms a gel and is easily digested/fermented by the bacteria in the colon
Insoluble fibre?
Does NOT dissolve in water or form a gel and is LESS readily fermented
Does digestion of carbs occur in the stomach?
Not chemical - the acid inactivates salivary amylase
How do glucose, galactose and fructose enter the blood?
Galactose and glucose require active transport to be brought into cells via the SGLT 1.
Fructose enters the cell by Facilitated diffusion
All exit the cell into the blood by facilitated diffusion to the liver where galac and fruc are isomerised into glucose
What does lactose intolerance occur?
Malabsorption due to lactase enzyme deficiency
Where is the gene for lactase expressed?
ONLY in the small intestine enterocytes which they then express at the brush border
Describe how lactose intolerance has occurred
- young have a lot of expression of lactase. Milk is their only food source
- after weaning expression usually down regulates
- in some ethnicities especially caucasian people continue to have elevated lactase expression into adulthood (lactase persistence)
- thought to be because they domesticated cows and consumed milk into adulthood so by natural selection lactase persistence was selected for
- if gene was inherited then most of the lactose ingested is not digested and absorbed and continues into the SI and LI where it is fermented by gut bacteria > methane, CO2, H2 causing the symptoms of gas and bloating as well as an excess amount of short chain fatty acids that don’t get absorbed and stay in the gut lumen
- the unabsorbed lactose and fermented products cause an increase in osmotic pressure and cause an osmotic diarrhoea
2 ways lactose intolerance can occur (via lactase deficiency)
- congenitial - autosomal recessive
- temporary lactose intolerance after infection and damage of villi where the enz is expressed (antibiotics can also cause this)
Lactose intolerance treatment?
Remove from diet. Many alternatives and lactose reduced milks
2 types of sugars?
intrinsic and added (don’t provide nutrients like the natural sugars do)
What can a high fibre diet assist in?
Maintaining healthy body weight
How does a high fibre diet assist in maintaining healthy body weight?
Normally fibre rich foods are bulky so take time to chew and fills us up without yielding excessive energy (aren’t digested so don’t contribute any monosaccharides and so little energy)
Soluble fibre
- inhibits absorption of cholesterol (along with plant sterols) as binds cholesterol esters so reduces LDL and total cholesterol
- when bacteria ferment soluble fibre they produce bi-products that are beneficial for bowel health including short chain fatty acids. These are good for the health of the enterocyte and reduce the risk of cancer
- soluble fibre binds fatty acids
- prolongs gastric emptying time so you feel full for longer
- regulates blood sugar by slowing transit time and so more time to uptake glucose
Where would you get soluble fibre from?
Skin of apple, lentils, beans, oatmeal, chickpeas, strawberries
What kind of fibre do we want in our body?
BOTH - they have different roles in the body but are both important for bowel health
What is metamusilin?
An example of something you would describe as a soluble fibre substitute. A husk that you add to water and thickens to a gel. Helps constipation
Insoluble fibre?
- plant fibres attract water producing a large and soft stool, giving mass to stool and making it easier to eliminate
- if you don’t have enough insoluble fibre you can get constipation leading to haemorrhoids due to exertion of excessive pressure in the LI during defecation
- INCREASES bowel transit time so aids in bowel peristalsis also important for constipation
Where do you find insoluble fibre?
Wholegrain complex carbohydrates
Bread, wheat, bran, potatoes
What do we want to change our intake of simple sugars to?
5% from 10-15% (due to obesity epidemic)
45-65% of total energy intake
How are they trying to decrease simple sugar intake?
Population guidelines
Less added sugars, fruit juices and syrups to 25g a day (6 tsp a day) currently it is 45g!
Hard to talk about specific amounts so try to reduce sweetened beverage intake at a POPULATION level
Why is oral health important?
- sugar decays
- poor oral health makes it difficult to eat good food!
- some places do not have fluoridated water
- sugary foods usually have a low pH as well
Describe a high glycemic index diet
- high sugar intake so spike in insulin response, sugar into cells, so blood glucose drops after quickly peaking
- get steep peaks and troughs of blood glucose and insulin
- hungry fast so snack and same thing happens
- peaks and trough not good for INFLAMMATION and health
Describe a low glycaemic index diet
- complex carbs/low sugar
- the break down and uptake of sugar is slower so blood glucose plateaus and insulin response isn’t as high
- less steep curve
- blood glucose is sustained for a longer time and you don’t get hungry
- this is important in health and in maintaining blood glucose but also in controlling hunger
How does exercise impact insulin?
Has a similar effect to a low sugar diet - sustained release/plateau, no peaks
Why is this important in type 1 and 2 diabetes?
Don’t want peaks and troughs of BG levels as this negatively impacts blood vessel integrity and long term METABOLIC health
Summary of what I should know for the carbs lecture
- carbs are an important food staple for many cultures
- carbs are the number our source of energy
- all carbs abs as monosacchs at enterocyte
- Food sources have different health effects
- Dietary fibre is important in maintaining bowel health
- Excessive simple sugars in the diet can have adverse effects on health
