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what are the functions of lipids in food?
- essential fatty acids
- econcetrated energy
- carry fat soluble vitamins
- falvour, texture, aroma
- satiety
- emulsification (PLs)
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what are the metabolic functions of food?
- adipose tissue = energy storage
- cell membranes
- nerve impulse transmission
- eicosanoid synthesis
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what is a monounsaturated fatty acid (MUFA)?
- contains 1 double bond between carbons
- ex. oleic acid C 18:1, n-9
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what is a polyunsaturated fatty acid (PUFA)?
- contains 2 or more double bonds between carbons
- ex:
- linoleic acid C18:2, omega 6
- common food sources = sunflower, safflower, corn and soybean oils
- alpha linolenic acids C18:3, omega 3
- common food sources = soybean and canola oils, flaxseed, walnuts
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what is hydrogenation?
- chemical process that adds H to monounsaturated or polyunsaturated fatty acids to reduce the double bonds
- make sit more saturated and resistant to oxidation
- more solid
- protects against rancidity
- produces trans fatty acids
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what is a cis fatty acid?
- has hydrogens on the same side of the // bond
- most naturally occurring unsaturated fatty acids in foods are -cis
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what is a trans fatty acid?
- has H on opposite sides of the // bond
- more linear
- occur in partially hydrogenated foods when H atoms shift around some // bonds to change from cis to trans
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what are the 2 essential fatty acids?
- linoleic acid = C18:2 n-6
- alpha linolenic acid = C18:3 n-3
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what are the functions of eicosanoids?
- n-6 family (linoleic)
- ↑ blood clotting
- ↑ platelet aggregation
- ↑ blood pressure
↑ CVD RISK
- n-3 family (alpha linolenic) (fish oil)
- ↓ blood clotting
- ↓ platelet aggregation
- ↓ blood pressure
↓ CVD RISK
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what doe the gall bladder do?
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how is fat emulsified by bile?
- 1. in the stomach, the fat and the water GI juices are separated
- the enzymes in the GI juices cannot get to the fat
- 2. when the fat enters the small intestine, the gall bladder secretes bile
- bile has an affinity for both water and fat so it acts as an emulsifier to bring fat into the water
- 3. bile converts the large fat globules into small droplets that repel one another
- 4. after emulsification, more fat is exposed to the enzymes in the GI juices, making fat digestion more efficient
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how is a triglyceride digested via hydrolysis?
- the triglyceride and 2 H2O molecules are split
- hydrolysis beaks the ester bonds
- its leaves 1 monoglycerides and 2 fatty acids
- the monoglycerides and 2 FAs are what is going to be absorbed in the intestinal cells
- sometimes the mono glycerol is split to give a 3rd fatty acid + glycerol
- FAs, mono glycerols and glycerols are absorbed into the intestinal cells
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how is fat absorbed?
- 1. glycerol and small lipids like short- and medium chain FAs can move directly into the bloodstream
- 2. large lipids like monoglycerides and long chain FAs combine with bile, forming micelles that are sufficiently water soluble to penetrate the watery solution that bathes the absorptive cells.
- the lipid content of the micelles diffuse into the cells and the free FAs and monoglycerides re-form "new" triglycerides
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what is the composition of a lipoprotein?
- contains an interior of triglycerides and + cholesterol and an exterior of phospholipids
- arrangement of hydrophobic molecules on the inside and hydrophilic molecules on the outside allows lipids to travel through the watery fluids of blood
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what are the different sizes of lipoprotein?
- chylomicron = biggest, more triglyceride /less protein, least dense
- vldl = 1/2 triglycerides
- ldl = 1/2 cholesterol (bad)
- hdl = 1/2 protein (good cholesterol)
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how doe slipped transport work via lipoproteins?
- 1. the liver cells can receive the small lipids directly from the intestine
- 2. intestinal cells form chylomicrons from dietary lipids
- 3. chylomicron deliver dietary lipids (triglycerides) to most of the cells in the body
- 4. cells all over the body (muscle, fat cells) remove triglycerides from the chylomicron as they pass by, so the chylomicrons get smaller and smaller and become chylomicron remnants.
- 5. liver cells remove chylomicron remnants from the blood
- 6. liver cells make lipids (cholesterol, fatty acids)
- 7. liver cells that make lipids with the chylomicron remnants are packaged with proteins that make vldl
- 8. vldl is shipped to other parts of the body (muscles, fat cells)
- 9. as vldl travels in the body, cell remove triglycerides causing vldl to shrink into ldl
- 10. ldl delivers cholesterol to the liver or to body cells (muscle)
- 11. liver cells make hdl, which pick up cholesterol form the body cells
- 12. hdl deliver cholesterol for recycling or excretion
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how do we get rid of cholesterol?
- by biliary excretion
- make more efficient by taking dietary fibre because body cannot break it down
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what is an adipose cell?
- newly imported triglycerides frist form small droplets at the periphery of the cell, then merge with the large, central globule
- as the central globule enlarges, the fat cell membrane expands to accommodate its swollen contents
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what happens in the fed state? (anabolic)
- ↑ insulin
- ↑ chylomicrons
- ↑ fat synthesis = lipogenesis in the liver from glucose and amino acids
- ↑ VLDL released
- lipoprotein lipase on adipose cells captures circulating TGs for storage
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what happens in the fasted state? (catabolic)
- ↓ insulin
- ↑glucagon
- ↑ hormone sensitive lipase in adipose cells hydrolyses TGs (lipolysis) and releases FAs and glycerol
- cells oxidize FAs (B-oxidation to acetyl CoA)
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what are the steps in arteriosclerosis?
- Healthy
- smooth walls
- elastic with heart beat
- wide = smooth muscles can expand
- Inflammation
- can produce ulcers / blood clots
- rough
- rigid
- narrow
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what are some risk factors for arteriosclerosis?
- gender (premenopausal)
- age
- genetics
- Modifiable risk factors
- smoking
- stress
- sedentary
- obesity - visceral
- hypertension
- high LDL/ low HDL
- homocysteine (take some vit.B)
- glucose intolerance
- chronic inflammation
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what are some high risk dietary characteristics?
- high energy (calories) = promotes obesity
- high fat = saturated fat
- high alcohol = ↑ inflammation
- low complex CHO/fiber
- low (high) vitamins/minerals = ↑ oxidative stress
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how do we monitor cholesterol status?
- cholesterol synthesis
- ↑ by sat. fat
- ↓ by MUFA and PUFA
- statins inhibit the enzyme HMG-CoA reductase
- ezetimibe inhibits the absorption of cholesterol
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DRI summary for fat
- no AI or UL = insufficient date to link level with prevention of chronic disease
- intake should be 20-35% of energy for adults (up to 40% for toddlers)
- saturated fat = low as possible
- trans fat = low as possible
- N-6 PUFA - 5 to 10% of energy (12-17g)
- N-3 PUFA - 0.6-1.2% of energy (1.1-1.6g)
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