7: Lipids Flashcards
Types of Lipids:
Structure and Composition of Triglycerides
- main dietary lipid
- glycerol backbone with three fatty acids attached to it
- Fatty acids differ in degree of saturation, length, or geometric organization
Types of Lipids: Triglycerides
Degree of Saturation of Fatty Acids
- saturated fatty acids = no double bonds (saturated with hydrogens)
- unsaturated fatty acids = one (mono)or more (poly) double bonds
- polyunsaturated fatty acid are named according to where double bond is (counting from omega end)
Types of Lipids: Triglycerides
Essential fatty acids
- human body cannot synthesize PUFAs with the double bond before the ninth position, therefore essential
- two essential fatty acids: alpha-linoleic acid (omega-3) and linolenic acid (omega-6) - can be used to synthesize other omega-3/-6s
- used to synthesize signalling molecules called eicosanoids
Types of Lipids: Triglycerides
Length of Fatty Acids in Food
Found in:
- Long-chain fatty acids: variety of animal products, some plants
- Medium-chain fatty acids: tropical oils
- Short-chain fatty acids: made by bacteria when they ferment indigestible carbs
Types of Lipids: Triglycerides
Lengths of Fatty Acids
LCFAs: 14+ carbon atoms
MCFAs: 6-12 carbon atoms
SCFAs: 2-4 carbon atoms
Types of Lipids: Triglycerides
Geometric Structure of Fatty Acids
- fatty acids are named based on their geometirc organization
- Unsaturated fatty acids can be either cis- or trans-fatty acids
Types of Lipids: Triglycerides
Fatty Acids - Hydrogenation
- food industry converts cis-fatty acids into trans-fatty acids (resemble saturated fatty acid)
- done because trans-fatty acids are more stable and therefore have a longer shelf life
- artificial/industrial trans fats significantly increase risk of CVD
Geometric structure differences between a cis- and trans-fatty acid
Location of where hydrogens lie in space around the double bond
Cis-: hydrogens on same side of the double bond - produces a kink
Trans: hydrogen atoms are on opposite sides of double bond - no kink
Types of Lipids: Triglycerides
Structure, function, source of Sterols
- hydrocarbon chain arranged in a ring formation
- variety of structural and functional roles in the body (cell membrane structure, hormone formation)
- source from both plant/animals
Types of Lipids: Triglycerides
Animal-Derived Sterols
Cholesterol: most common animal-derived sterol
Types of Lipids: Triglycerides
Animal-Derived Cholesterol
- a third of human cell membrane is composed of cholesterol
- Precursor for vitamin D
- Precursor for estrogen, testosterone
T/F: Cholesterol is not considered an essential nutrient
True, liver and other body tissues can synthesize their own cholesterol, so it is not needed from the diet
Types of Lipids: Triglycerides
Plant-Derived Sterols
- AKA plant sterols, phytosterols
- Slightly different molecular structure than animal-derived sterols
- Found in unrefined vegetable oils, nuts, seeds, fruits
•May limit the absorption of animal-derived sterols when consumed
Types of Lipids: Triglycerides
Structural differences of Phospholipids vs Fatty Acids
- share many structural similarities
- both have fatty acids attached to a glycerol backbone
- triglyceride has 3 fatty acids, while the phospholipid has 2 fatty acids; in the place of the third fatty acid there is a phosphate group
Types of Lipids: Triglycerides
Phospholipids
- amphiphilic nature (hydrophilic and a hydrophobic end) gives them special properties and functions
- form bilayer when immersed in water
- act as emulsifiers
- carry lipids around body (lipoproteins)
T/F: Triglycerides are completely hydrophobic, whereas phospholipids are not
True, phospholipids are amphiphilic. Fatty acid groups are hydrophobic, while phosphate group is hydrophilic
Types of Lipids: Triglycerides
Phospholipid Bilayer
phosphate heads facing the watery environment and fatty acid tails facing each other
- Only water and non-polar substances (fats) can readily pass through this membrane. Most other molecules and ions are not able to pass through the bilayer unless there is a transporter
What nutrients require a protein transporter to move from one side of the cell to the other
Carbohydrates, amino acids, minerals and water-soluble vitamins require a protein transporter (and potentially energy)
Lipid Digestion Process
Mouth: lingual lipasae chemically digests MCFAs/SCFAs, mechanical digestion separates FA from 3glerceride
Stomach: gastric lipase digests MCFAs/SCFAs
Small Intestine: Majority lipid digestion - bile emulsifies lipids, and pancreatic lipase digests remaining lipids
Large Intestine: minimal lipid digestion and absorption
Lipid Digestion: Micelle
Lipid Digestion: what can be found in Micelle
Sterols, fat-soluble vitamins (A,D,E,K), glycerol, FA, and other hydrophobic structure
Lipid Absorption
- Micelle breaks down. Lipid contents absorbed into small intestine cells through passive diffusion
- Lipids wrapped in phospholipids and exit small intestine cell and enter centre of villus. Resulting in structure called chylomicron (lipoprotein)
- Chylomicrons are too large to enter blood so they enter lacteals
Lipid Absorption:
What is a Lipoprotein
Specific lipoprotein is a Chylomicron
- lipid components exiting small intestine, wrapped in membrane composed of phospholipids
Lipid Transport
- Transporting lipids requires a series of lipoprotein molecules
- hydrophobic nature of lipids makes them incapable of dissolving in the watery environments of the small intestine lumen, blood and lymph
What nutrient is most dense and least dense
Most dense - protein
Least dense - lipids
Lipoproteins - lipid transport of VLDL
“Very Low Density Lipoprotein”
- made in liver —> body cells —> becomes LDL as it looses TGL
- mainly delivers triglycerides
Lipoproteins - lipid transport of Chylomicron
From small intestine villus → lymph → blood → body cells → liver
- mainly delivers TGL
Lipoproteins - lipid transport of LDL
“Low Density Lipoprotein”
From VLDL → delivers cholesterol to body cells OR returns to the liver OR gets deposited in artery walls
- Mainly delivers cholesterol; AKA ‘bad cholesterol’ because it can build up in artery walls
Lipoproteins - lipid transport of HDL
“High Density Lipoprotein”
Made in liver → picks up cholesterol from body cells → returns it to the liver
- Mainly removes cholesterol from blood, body cells; AKA ‘good cholesterol’ because it lowers the build of cholesterol in artery walls
What lipoprotein have the most triglyceride
very low-density lipoproteins (VLDL) have the most triglycerides
high-density lipoproteins have the least triglycerides
Lipoprotein: Chylomicrons (CM)
- transport lipids between small intestine and liver
- contain lipids too large to enter blood vessels of villi so are absorbed into lacteals - one-way lymphatic vessels found within the villi
- Once deposited into bloodstream from the lymphatic vessels, they circulate through body, dropping off lipids to body tissues as needed
Define lipoprotein lipase (LPL) and its location
An enzyme at Blood vessels near lipid-desiring tissues (muscle, fat tissue)
- promotes uptake of lipoprotein contents, particularly fatty acids, into cells
Lipoproteins transport and deliver lipids
- CM = largest lipoprotein. Deliver TGLs from small intestine to body cells
- Tissues: enzyme LPL break TGLs into FA and glycerol to absorb out of CM and into tissue. CM becomes smaller
- Remaining CM returns to liver breaking down into its components
- Liver reassembles TGLs, chol, pro, PPL into VLDL. VLDL is main TGL delivery system from liver to tissues
- Tissues: LPL break down TGLs, allowing components to enter cells
- VLDL become smaller since lose TGLs = more dense to form LDL , main chol delivery system
- 3 fates of LDL: a. Cells take LDL
B. LDL returns to liver, to break down
C. LDL levels too high, sticking to artery walls - Liver makes HDL. HDL high in pro, low in TGL. HDL picks up chol from body cells/lipoprotein and return to liver
What is Atherosclerosis and its cause
Heart attacks / strokes
- LDL levels too high becoming oxidized, sticking to artery walls, narrowing them and increasing risk of atherosclerosis
What is bad/good cholesterol
Bad: LDL (primary chol delivery), chronically high levels become reactive and build up in artery walls, promoting CVD
Good: HDL pickup chol as it travels through bloodstream, return it to liver, thus lowering amount of chol circulating in blood. Higher levels lower risk of CVD
Lipid Functions:
Energy Provision
- provides 9 kcal/g
- adequate carbs: TGLs metabolize, products enter citric acid shovel and electron transport chain yield ATP
- inadequate carbs in diet: ketones form
Lipid Function:
Lipid storage vs lipid metabolism
- energy surplus, extra energy is stored as lipid in adipose tissue
- energy deficit, lipids are retrieved from adipose tissue - metabolized to capture energy as ATP to fuel body’s needs
Lipid Function:
Membranes
Membranes of cells and membranes of cellular organelle are composed of phospholipids
- regulating what can pass into and out of that cell
Lipid Function:
Transport/Storage of Fat Soluble Vitamins
Vitamins A,D,E,K are fat-soluble
- packaged, absorbed, transported with other dietary lipids within micelles (small intestine) and lipoproteins (blood)
- no immediate need, stored in adipose
- hydrophobic, requires lipoprotein transport
Lipid Function:
Cholesterol-derived molecules include
Steroid hormones, bile salts, vitamin D, estrogen, testosterone
Lipid Function:
Essential fatty acid-derived molecules include
Omega-3, omega-6 FAs used to synthesize a wide range of eicosanoids
eicosanoids, endocannabinoids
- effects on blood vessels, blood clotting and inflammation
Lipids and Health:
Lipids and CVD
CVD compromises cardiovascular systems ability to deliver cellular needs (oxygen, nutrients) and removes waste (CO2)
- certain lipids can increase/decrease risk of developing atherosclerosis
How do decrease risk of CVD
- not smoking, consistent exercise, maintaining a healthy weight and managing stress levels
- Consuming a diet rich in whole foods with lots of vegetables and fruits
- certain lipid and non-lipid dietary factors can affect the risk
Lipids and Health:
Trans Fatty Acids and CVD
Known to increase:
-ratio of LDL to HDL
- risk of CVD (mortality)
- minimize consumption of NOVA 3/4 especially hydrogenated foods
Lipids and Health:
Saturated Fatty Acids
Diets high in saturated fat:
- Increase LDL → increases risk of CVD = lipid hypothesis (direct link between saturated fat and CVD has not been established)
- Replacing saturated fats (mainly found in animal products) with unsaturated fats (mainly found in plant products) may lower potential risk
Lipids and Health:
Polyunsaturated Fatty Acids
- When PUFAs replace saturated fat, LDL levels decrease
- whole foods-based diet rich in plants Ex: nuts, seeds, vegetable oils, fatty fish, salmon, trout = higher in PUFAs
Lipids and Health:
Essential Fatty Acids
Omega-3 fatty acids:
- several cardioprotective effects (decreasing inflammation, blood cholesterol, vasoconstriction, blood clotting)
- supplementation of omega-3 not been shown to decrease cardiovascular events
Omega-6 fatty acids:
- increase risk of CVD because they Increase inflammation/blood clotting
- results of RCTs have been mixed
Both omega-3 and omega-6 fatty acids have protective effects on the brain
- being studied for potential to improve brain health, reduce risk of Alzheimer’s, etc.
Lipids and Health:
Cholesterol
Dietary chol has minimal effect on increasing LDL / cardiovascular risk
- body makes less chol when more is consumed, LDL levels don’t rise
- However, 25-30% of people are believed to be chol hyper-responders = LDL go up when more cholesterol is consumed
T/F: To reduce LDL cholesterol, less dietary cholesterol must be consumed
False, We do not eat LDL; the liver makes it from available lipids.
- most people, dietary cholesterol has a minimal effect on increasing LDL and cardiovascular risk
Lipids and Health:
Eggs and Cardiovascular Health
- extremely nutrient dense (75 kcal/egg = high in protein, fat, vitamins, minerals)
- May also be high in omega-3 fatty acids if chickens are fed flaxseeds
- Chickens converts alpha-linoleic acid to DHA
- Eggs are also high in chol (225 mg/egg)
- most people, higher chol consumption does not increase LDL
- In moderation (1-3 eggs per day), they do not seem to increase risk of CVD
Lipids and Health:
Plant Sterols
- Reduce LDL levels by competing with chol for absorption and altering chol metabolism
- Whether this leads to a reduction in CVD risk/mortality has not been established
Lipids and Health:
Effect on Cardiovascular Health - Omega-3 Fatty Acids
Cardioprotective: reduce inflammation, blood cholesterol and blood clotting, while promoting vasodilation
Ex. flax seeds, chia seeds, fatty fish, fish oil
Lipids and Health:
Effect on Cardiovascular Health - Omega-6 Fatty Acids
Increase inflammation and blood clotting, which may compromise cardiovascular health
Ex: soy, corn, vegetable oil
Food sources with Cholesterol
Eggs, shellfish, animal products
Lipids and Health:
Lipids and Obesity
- No single nutrient causes obesity
- total energy consumed which affects likelihood for fat gain (energy surplus) or fat loss (energy deficit) from body
Recommendations for Lipid health
- AMDR recommends that 20–35% of calories come from lipids
- Consume most lipids from whole sources
