Lecture 11 Flashcards
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)
phospholipid
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
Butter
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
Sterols
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),
- lecithin (phospholipid present in bile and in food membranes) and
- monoacylglycerol (2HMAG; breakdown product from TAG).
Catalysation of Lipid digestion
Lipid digestion in the adult small intestine is catalysed by three enzymes
- 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.
- 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).
- 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.
