Lecture 12: Fat nutrition, digestion and absorption Flashcards
What are the lipids in the diet?
- Triglycerides
- Phospholipids
- Cholesterol
- Cholesterol esters
- Fat soluble vitamins
How much energy does fat supply?
37Kj/g i.e double rest
What does a triglyceride consist of?
3 FA bonded to glycerol
Where are long, medium and short chain FA found?
Long = Found primarily in meat, fish and vegetable oils.
Medium and short chain FA found in diary products
What influences the characteristics of fats?
- Short or long chain
- Saturated, mono-unsaturated, polyunsaturated, CIS/TRANS
What are sterols?
Multiple ring shaped structures
What is cholesterol found in?
Animal foods only. (Is a sterol)
Plant based sterols can interfere with cholesterol absorption i.e logical and flora proactiv.
What are ring sterols used for?
- Starting material for bile, sex hormones, adrenal hormones and Vit D
- Structural component of cell membranes
How much cholesterol is produced daily?
Liver produces 800-1500mg of cholesterol daily
What can cholesterol cause?
Atherosclerosis when Cholesterol forms deposits on the vascular walls.
Describe fat digestion;
1) Lingual lipase (acid stable)
2) Gastric lipase
3) Stomach muscle contractions disperse fat into smaller droplets.
4) CCK stimulates bile release and fat emulsification
5) Pancreas releases pancreatic lipases
6) SI absorbs fats after they are digested / emulsified.
During this process fats form mixed micelles which are important in the absorption process.
What are the 3 pancreatic enzymes?
Pancreatic lipase
- (TAG->Glycerol and FA), (require pancreatic enzyme colipase to be active.)
Pancreatic cholesterase,
- remove FA from; cholesterol esters, 2-MAGS, TAG containing short / medium chain FA, fat soluble vitamins (A, D3 and E).
Phospholipase A2;
- Removes FA from 2 pos. on phospholipids.
What happens to bile salts during digestion?
Stored in the liver between meals, Absorbed mainly in the terminal ilium and re-used via the enterohepatic circulation
What are the four roles of bile during fat digestion?
1) Emulsification of fat droplets
2) Form mixed micelles (Removing the products of fat digestion from lipid droplets i.e 2-MAG, cholesterol etc)
3) Cofactors for lipase activity
4) Aid absorption (Mixed miscelles increase the delivery rate of FA digestion products across the enterocyte membrane)
Describe fat absorption;
Fat digestion results in the formation of glycerol, FAs, cholesterol which with the emulsification effect of bile form micelles, micelles get near the apical membrane and allow the diffusion of the digestion products into the cells.
Once in the cell the FAs and glycerol are resynthesised into TAG which are packaged into chylimicrons and delivered into the lymphatic system.
i.e in the gut lumen fats must be broken down into their basic units with the help of lipases and bile salts. These can freely diffuse into the cells, but are repackaged into TAG / cholesterol and then chylimicrons for delivery into lacteals
What is packages into chylomicrons?
Cholesterol, fat soluble vitamins (A,D,E and K), Apolipoproteins
What are micelles?
Monoglycerides and long chain fatty acids combine with bile forming micells that are sufficiently water soluble to penetrate the watery solution that bathes the absorptive cells. There the lipid contents diffuse into the cells.
How much of cholesterol is made by the liver?
80%
How are fats transported in the blood?
Lipoproteins, of which the largest are chylomicrons.
- Very low density lipoproteins (VLDL) (primarily of triglycerides)
- Low density lipoproteins (LDL) (Compose primarily of cholesterol)
- High density lipoproteins (HDL) (Composed primarily of proteins)
What are the general recommendations for fat?
- Limit saturated and trans fats (<10% total)
- Choose lean healthy foods
- Low fat, trim visible fat and cook without oils
- Avoid low fat high sugar foods
- Mediterranean diet
What are the essential fats?
Alpha-linolenic acid (Omega 3) Linoleic acid (Omega 6)
Why are fats important?
- Major energy source and fuel store
- Required for transporting fat soluble vitamins
- Provide essential fatty acids - Linoleic acid and alpha linolenic acid
- Important for insulating and protecting the body
Why are linoleic acid and alpha linolenic acid important?
- They share enzyme pathways to eventually produce eicosanoids which have roles in pro-inflammation and anti-inflammation.
The essential FA are polymerised. The intermediates can be consumed and gained in diets.
Whats the implication of sharing an enzyme system?
Over consumption of one FA will prevent the other essential FA from accessing the enzymes and forming its products.
Omega 6 = Proinflam
Omega 3 = Anti-inflam
Thus long term will shape these profiles if diet imbalance and change risk for conditions.
