Lecture 11 Flashcards Preview

Digestive System Module > Lecture 11 > Flashcards

Flashcards in Lecture 11 Deck (32):

Adult fat intake

Adult fat intake varies from 25g/day (12% of calories) in riceHbased diets to as much as 140H160 g/day (40% of calories) when some meat and dairy produce are readily available such as in the NZ diet.


What are the lipids of our diet?

triacylglycerol (TAG)
cholesterol and cholesterol esters
fat soluble vitamins


Fat digestion and milk

Fat digestion is also important in milk dependent neonates, when fat provides some 40% of the calories (fat is 3H4% w/v in milk), and the milk fat composition is different from plant or meat fats


What are the Key concepts of Fats

• Major energy store and fuel source. (largest energy per/gram out of all macronutrients-alcohol, protein, carb. More calories)
• Required for transporting fat soluble vitamins (A, D , E , K, in dietary fat, tranporting and stroging vitamins)
• Provide Essential Fatty acids Linoleic and alpha linolenic acid (cannot manufacture in our body. important for production of cell membranes, CNS and brain development)
• Important for insulating and protecting the body (below certain body fat % more likely to die/damage vital organs)


What is fat?

The chemical structure of fat (lipids) is diverse.
Triglycerides (fats and oils-Fatty acids) are the most common type of lipid found in the body and in food (dietary fats) Methyl end + acid end
Each triglyceride molecule consists of 3x fatty acids bonded to glycerol.
Phospholipids and sterols (including cholesterol) are also classified as lipids but their structures can be quite different.


Fatty Acids

Dependant on chain length + position of double bonds (give them their properties)
Fatty acids are found in the main form of lipids – triglycerides.
• Long chain fatty acids are found primarily in meat, fish and vegetable oils.
• Medium and short chain fatty acids are found in dairy products.


Chemistry and State of Fatty Acis

The chemistry of a fatty acid – whether it is short or long, saturated or unsaturated and location of
double bond – influences the characteristics of foods and the health of the body.
• Polyunsaturated fats are liquid at room temperature.
• Shorter fatty acid chains are softer at room temperature than longer chains.
• Monounsaturated fat is slightly less susceptible to spoilage.
• Polyunsaturated fat spoils most readily.


Saturated fats

-no double bonds makes them solid at room temp
-more resistant to oxidation (longer shelf life + more useful to keep/store (at room temperature))
Coconut Oil
Beef Tallow
Palm Oil
Lard (meat fats)


Monosaturated Fatty acids

Olive Oil
Canola Oil
Peanut Oil
-liquids at room temperature
-slightly less susceptible to spoil
-hydrogenation (double bonds unstable at high heats and H's add) -protects against oxidation (more saturated fats like/trans) (therefore prolonging shelf life) + alters texture


Polyunsaturated fatty acids

Safflower oil
Flaxseed oil
Walnut oil
Sunflower oil
Corn oil
Soybean oil
Cottonseed oil
-liquids at room temperature
-spoils most readily
-predominantly contains omega 6>omega 3



Multiple ring structure + some other fatty acids
A well known sterol is cholesterol.
Found in plant and animal foods.
Cholesterol is found in animal foods only – meat, eggs, fish, poultry and dairy products (exogenous). (make more
Plant based sterols can interfere with cholesterol absorption.
Material for bile acids and hormones (steroid hormones (vit D- essential for health))
- Examples include Logicol and Flora Proactiv.


Role of Sterols

• Starting material for bile acids(digestion), sex hormones, adrenal hormones and vitamin D.
• Structural component of cell membranes.
• Liver produces 800 to 1500 mg cholesterol per day (endogenous).
• Atherosclerosis is a disease that causes heart attacks. It occurs when cholesterol forms
deposits in the artery wall.


Fat Digestion

In the stomach some TAG digestion occurs in gastric juice due mainly to the gastric lipase.
The fatty acids (FAs) released partly control gastric emptying.
In the small intestine, the pulses of chyme from the stomach are immediately neutralised in the duodenum by bicarbonate from the pancreatic juice and bile.
The food fat is further emulsified (droplet size decreased and surface area increased).


Major Emulsifying agents

major emulsifying agents are the 1. bile salts (from liver by way of gallbladder storage),
2. lecithin (phospholipid present in bile and in food membranes) and
3. monoacylglycerol (2HMAG; breakdown product from TAG).


Catalysation of Lipid digestion

Lipid digestion in the adult small intestine is catalysed by three enzymes
1. Pancreatic lipase digests triglycerides (triacylglycerols or TAGs) to glycerol and free FAs, and requires an additional protein colipase from the pancreas (activated from proHcolipase) to become active.
2. Pancreatic non-specific esterase (cholesterolesterase) removes FAs from cholesterol esters, 2HMAGs, TAGs containing short and medium chain fatty acids, and fat soluble vitamin esters (Vit A, D3, E).
3. Phospholipase A2 removes an FA from the 2 position of phospholipids (eg. lecithin is degraded to lysolecithin).
-In addition, there is a lipase in human milk called human milk lipase (not present in ruminant milk) which is important in breast fed human neonate nutrition. This lipase from the mother’s milk is stable during passage through the acidic conditions of a baby’s stomach, and it only becomes active in the small intestine, as this activity is bile saltHdependent.


Lipase in milk

there is a lipase in human milk called human milk lipase (not present in ruminant milk) which is important in breast fed human neonate nutrition. This lipase from the mother’s milk is stable during passage through the acidic conditions of a baby’s stomach, and it only becomes active in the small intestine, as this activity is bile salt dependent.


Stearic acid

18 carbon
Saturated fatty acid
-found in meat
-no double bonds as all are saturated


Oleic acid

18 carbon
monounsaturated fatty acid
-found in olive oil
-1x double bond


Linoleic acid

18 carbon
polyunsaturated fatty acid
-an essential fatty acid
multiple double bonds


Plant oils

the polyunsaturated fats are heated to high levels/
hydrogenation occurs and H's are added to the double bonds
become more saturated/trans fat like in out body
-not good for health
-but good for shelf life


Coconut Oil

Highest content of saturated fat
-but not all saturated fats are equal


Dairy product fat

Saturated fats from dairy products/whole milk doesnt have a lipid profile with that high of a risk of CDV
vs palm oil etc
-where controversy lies


Flaxseed oil

Largest proportion of Polyunsaturated fats
different to most Poly-uns-fats as has larger omega 3>6
-best oil sources of omega 3
-oily fish + slamon



20% from food we eat. Foods contianing cholestrol are MEat, Eggs, FIsh, poultyr, dairy products
but 80% is Endogenous cholesterol, far more is made/manufactured in the liver/body (than eaten exo)
-plant based sterols- similar to cholesterol. interfere with cholesterol absorption. about 300mg daily.
-more plant matter = more plant based sterols consumed
-block bile acid reabsorption in bowel = intrahepatic circulation of bile acids = cholesterol not taken up by liver = liver has to produce its own cholestrol


Digestion of Fat in the mouth

Some hard fats begin to melt as they reach body temperature
the sublingual salivary gland in the base of the tongue secretes lingual lipase
+ some enzymes are released


Digestion of fat in the stomach

The acid-stable lingual lipase initiates lipid digestion by hydrolyzing one bond of triglycerides to produce diglycerides and fatty acids.
The degree of hydrolysis by lingual lipase is slight for most fats but may be appreciable for milk fats
The stomach's churning action mixes fat with water and acid
A gastric lipase accesses and hydrolyses (only a very small amount of )fat


Digestion of fat in the Small intestine

Bile flows from gall bladder (via common bile duct)
Fat -Bile--> Emulsified fat
Pancreatic lipase flows in from the pancreas (via pancreatic duct)
Emulsified fat (triglycerides) ---Pancreatic(and intestinal) lipase --> Monoglycerides, glycerol, fatty acids (absorbed)


Digestion of fat in the Large intestine

Some fat and cholesterol, trapped in fiber, exit in feces



very difficult to digest fat w/o bile (people w/o gallbladder prescribed low fat diets)
"washing liquid"
-breaks down fat into smaller particles.
-now more able to be picked up and acted on by enzymes (to be further broken down)


Action of Bile

Helps emulsify fat
once enzyme begins to attack, helps for into drops lefts and become hydrophobic.
-by being hydrophobic repels one another, stops attracting eachother, keeps them into individual small droplets
-also ensures that droplets become smaller,
-smaller droplets= easier for enzymes to break down -lipase attach onto fatty acids and break down into small components (which can then be absorbed)


Intrahepatic reabsorption of bile

continue to recycle bile
stored in gallbladder
secretes into SI (where emulsification of fat occurs)
Bile reabsorbed into blood
Bile is then made from cholestrol in liver
-Sterols (natural consume) block uptake of bile salts into liver/gall bladder
- due to interaction with soluble fibres, some bile is lost in the feces
-consuming large amounts of plants sterols, larger loss of bile in feces. Used with statins (medication for CDV) to reduce LDL cholesterol (cholesterol of risk in CDV)



Displipidemia currently associated with CVD
-more than just concentrating on fat and LDL