Fat Digestion Flashcards
What are the key concepts of Fats
1) major energy store and fuel source
2) Needed to transport fat soluble vitamins (A, D, E, K)
3) Provide essential FAs (linoleic acid) that cannot be manufactured anywhere else
4) Insulate and protect the body (as below a certain body % we die!)
What are the properties of FAs dependent on?
- number of carbons
- Placement of double bonds
Can be saturated, monosaturated, polysaturated
What types of fatty acids are solid @ room temp
Saturated FA (no double bonds)
Types of FAs liquid @ room temp
unsaturated FA (mono/polysaturated)
Two types of Lipids
Triglycerides (fats & oils)
Sterols
Most common type of lipid
Triglycerides ( 3 FA bonded to glycerol)
Long-chain FA are found in
meat, fish, vegetable oils
medium and short chain FA are found in
dairy products
Saturated fats
- Solid @ room temp
- more resistant to oxidation
Unsaturated fats
Polyunsaturated : liquid @ room temp, spoil most readily
Mono saturated: less susceptible to spoilage
What does hydrogenation do?
Forced chemical addition of hydrogen.
When heated US FAs become hydrogenated, become to act like saturated fats, eg) margarine
-Protects against oxidation pro-longing shelf life
Which oil has the highest % of saturated fats
Coconut oil, despite its fame within the health industry
Why can we not treat every FA the same?
Because they all have different ratios of FA types within them, there is a huge amount of variability
A well known sterol is _______, ___% is from the food we eat, and ___% is manufactured (endogenous)
A well known sterol is cholesterol, 20% is from the food we eat, and 80% is manufactured (endogenous)
Where is cholesterol found?
In animal foods only.
What do plant based sterols do?
As these are similar in structure, they block and interfere with cholesterol absorption.
We consume 30mg/day of PB sterol
They block the reabsorption of bile acids, disrupt the enterohepatic circulation of bile (which is made from endogenous cholesterol. This lowers cholesterol.
Where are sterols found?
In both plant and animals
Roles of sterols
1) starting material for bile acids, sex hormones, adrenal hormones and vit D
2) Structural component of cell membranes
3) liver produces 800-1500mg cholesterol per day (endogenous)
Athersclerosis
when cholesterol forms deposits in the artery wall. Causes heart attacks.
Fat digestion in the mouth…
Salivary glands release lingual lipase as we chew food. Also warmth of mouth softens fats
Fat digestion in the stomach…
acid stable lingual lipase initiates lipid digestion
a little gastric lipase produced and some enzymatic breakdown
muscle contractions/churning action of stomach- disperses fat into smaller droplets
Chyme begins to leave stomach, enters duodenum
Fat digestion in the small intestine…
CCK is released and signals the gall bladder to release bile (fat > emulsified fat)
secretin stimulates the pancreas to release enzymes eg) pancreatic cholesterase & pancreatic lipase,
Emulsified fat > monoglycerides, glycerol and Fatty acids
What are the actions of bile?
binds to droplets and repels them from each other. Keeps droplets small and makes it easier for enzyme (lipase) to latch on and break the down into smaller, absorbable contents
Recycling of bile in the liver
-bile stored in gall bladder
-emulsifies fat in SI
(if trapped in colon by soluble fibres it is lost as faeces)
-in liver, bile is made from cholesterol
How do sterols affect bile?
interfere with the uptake of bile salts to liver.
Cause us to loss more bile via faeces
Statins
Reduce production of cholesterol
What are plant sterols and statins used for?
To decrease CVD
Variation between absorbtion of FAs
Short and medium chain FA: can be absorbed directly through the enterocytes > blood supply of villi > portal vein
Long chain FA: pass into enterocyte via basolateral membrane (micelles) > ER to get repackaged into chylomicrons > lacteal > lymph system > blood
Chylomicron components are removed during circulation due to what?
Triglyceride hydrolises by lipases released from peripheral tissues
What happens to the chylomicron during circulation
Becomes smaller and denser, chylomicron remnants are endocytosed by the liver
Lipid transport is made possible by a group of vehicles called
lipoproteins
the largest of lipoproteins
Chylomicrons
VLDL are composed primarily of
Half triglycerides (eg chylomicrons)
LDL are composed primarily of
half cholesterol
HDL are composed primarily of
half protein
Structure of a chylomicron (a type of lipoprotein)
interior of triglycerides and cholesterol, surrounded by phospholipids
Hydrophobic tails on inside and hydrophillic heads on the outside allow lipids to travel through the watery fluids of the blood
Why do we want a higher ratio of HDL to LDL?
Because we want more protein and less TG’s and cholesterol
How much of our total energy intake from fat
35%
How much %fat should we be having daily?
20-35%
how much saturated fat, n-6 and n-3 FAs should we have daily
Saturated fats
1980s is relevant to cholesterol why?
its the year info about cholesterol and CVD came out
-strong association between saturated fats & CVD (also smoking)
FI response to reduce fat intake
low fat (high sugar) products. Fat replaced to carbohydrates (simple sugars) and now we have an obesity epidemic
FI response to reduce sat fat and cholesterol
change to vege oils, margarines, trans fats
How do large lipids (LCFA and monoglycerides) get into the enterocytes?
They combine with bile to for ‘micelles’, that are sufficiently water-soluble to enter the watery solution that covers the cell. Enters via BL membrane, diffuses into the cell
