Fats Flashcards
Unsaturated fats
Mono- one double bond. Found in avocado, peanut oil, most nuts eg. C18:1n-9
Poly- more than one double bond- least stable, found in sesame, soybean oils etc eg. C18:2n-6
Sterols (eg cholesterol)
Endogenous cholesterol-Made by the liver, not an essential nutrient
Exogenous cholesterol- from the diet, only found in food of animal origin
Phospholipid
Solubility in fat and water Non essential as liver can manufacture own Constitutes all cell membranes Component of bile Used as emulsifier
Plant sterols and Stanols
Interfere with cholesterol absorption by competing with cholesterol for uptake into micelles
Has cholesterol lowering properties
Eg. Leaves, nuts, veg oils
Lipid digestion
Goal is to dismantle triglycerides to form counterparts so that hydrophobic fat can be broken down by hydrophilic enzymes
Mouth- lingual lipase
Stomach- strong muscle contractions, gastric lipase hydrolyses fat into diglycerides and fatty acids.
Small intestine- cholecystokinin, gall bladder releases bile, bile acts as emulsifier. - pancreatic lipase. -hydrolysis of triglycerides and phospholipids. - bile routes, blood cholesterol levels
Large intestine- some fat and cholesterol trapped in fiber, exit in faeces.
Lipid absorption
Directly into blood stream
- glycerol and short and medium chain fatty acids
Lymphatic system
- micelles diffuse into intestinal cells
- reassembly of triglycerides
- packed with proteins - chlyomicrons
- bypass liver at first
Lipid transport
- chlyomicrons Largest and least dense Transport diet derived lipids Liver removed remnants from blood - very low density lipoproteins (VLDL) Made in the liver Proportion of lipid shift - low density lipoproteins (LDL) Cell needs Liver regulation -high density lipoproteins (HDL) Remove cholesterol from cells Carry cholesterol to liver for recycling Anti inflammatory properties
Role of triglycerides
Provides cells with energy Adipose tissue secretes hormones Skin insulation Shock absorption Cell membranes Cell signalling pathways
Lipid metabolism
Adipose cells store fat after meals
- lipoprotein lipase hydrolyses triglycerides
- triglycerides reassembled inside adipose cells
Using fat for energy
- protein soaring
- energy deprivation- fasting and ketone bodies
Hydrogenation of fat
Chemical process used to harden fats to prevent unsaturated fats from rancidity eg margarines
Problems:
No control over which db are broken
Formation of trans fatty acids (isomers) naturally found in very small amounts in nature
Lipid recommendations
15% of total energy
Considering essential fatty acids and fat soluble vitamins
UL:
Health effects of lipids
Heart disease- elevated blood cholesterol by saturated fats, monounsaturated can reduce this,
Cancer- promotion of certain types of cancers
Obesity- too many k- calories in fat
Ketogenic diet
High fat, adequate protein, low carb diet
Medically used to treat epilepsy in children
If there is very little CHO in diet, the liver converts fag into fatty acids and ketone bodies to provide brain with fuel. Leads to a reduction in the frequency of epileptic seizures
Ketosis
Elevated ketone bodies in the body
When glycogen stores are not available in the cells, fat (triglycerol) is cleaved to provide 3 fatty acid chains and 1 glycerol molecule in a process known as lipolysis
Most of the body is able to use fatty acids as an alternative source of energy in a process called beta oxidation
One of the products of beta oxidation is Acetyl CoA which can be further used
In the citric acid cycle.
During prolonged fasting or starvation, Acetyl coA in the liver is used to produce ketone bodies instead,
Leading to a stage of ketosis. The ketone body acetoacetate will slowly decarboxylate into acetone, a volatile compound that is both metabolised as an energy source and lost in the breath and urine. Ketone bodies are acidic and so, when in excess can lead to ketoacidosis which can potentially be fatal.
Structure of free fatty acids
Organic acid- chain of 4-24 carbon atoms with hydrogens attached
Acid group at one end, and methyl group at other
Foods contain a mixture but 18 carbon length is most common
Length and chemical structure affects stability of fat in foods and solid or liquid state at room temp - short chain solid at 25 degrees.
