Lipids Flashcards
(83 cards)
1
Q
What are the three major groups of dietary lipids?
A
- triglycerides
- phospholipids
- sterols
All of these are insoluble in water.
2
Q
What is the predominant type of dietary lipid?
A
- Most lipids (~95%) are consumed as mixed triglycerides
- FA can be 2 to 24 carbons in length: 18C = most commonly consumed
3
Q
What are the two groups of triglycerides/fatty acids?
A
Saturated fat (all carbon saturated with Hydrogen)
Unsaturated fat
4
Q
What are saturated fatty acids?
A
- all carbons (except acid end) are saturated with hydrogen atoms
- linear, pack well, solid at room temperature
- higher amounts in animal foods, tropical oils, chocolate, milk fats
5
Q
What happens when 1 fatty acid is hydrolyzed off a triglyceride?
A
A DIGLYCERIDE (DG) results
6
Q
What happens when 2 fatty acids are hydrolyzed off a triglyceride?
A
A MONOGLYCERIDE (MG) results
7
Q
What are the two major groups of unsaturated fatty acids?
A
Monounsaturated and Polyunsaturated
8
Q
What are mixed triglycerides?
A
- major fuel source for body
- ~95% of lipids in diet and in body are mixed TG
9
Q
What are Monounsaturated FA?
A
- 1 double bond in carbon chain
- cis double bonds occur in nature – hydrogens are on the same side of the double bond – creates a bend in the molecule
- MUFA don’t pack as tightly as SFA
- semi-solid at room temperature
- Omega-9
10
Q
What are some food sources for monounsaturated fatty acids?
A
- Olive oil
- Canola oil
- Avocado oil
- Peanut oil
- Almond oil
- Sunflower oil
11
Q
Where do you find oleic acid?
A
monounsaturated fatty acids
12
Q
What are polyunsaturated fatty acids?
A
- greater than 1 double bond in C chain
- multiple cis bonds, multiple bends in molecule, liquid at room temp.
- Linoleic acid
- Linolenic acid (α-LnA)
13
Q
Where do you find Omega-6 EFA, linoleic acid?
A
Polyunsaturated fatty acids
14
Q
What are dietary sources of Linolenic acid (α-LnA) Omega-3 EFA?
A
- Flaxseed oil
- Walnut oil
- Canola oil
- Hemp oil
- Wheat germ
- Fish oil
15
Q
What are food sources for linoleic acids?
A
- Corn oil
- Soybean oil
- Sunflower oil
- Sesame oil
16
Q
Is Linoleic acid essential?
A
Yes!
17
Q
What can linoleic acid be elongated into?
A
LA can be elongated & desaturated to longer chain Omega-6 FA - Arachidonic acid, C20:4
Linoleic acid is essential but Arachidonic acid is not!
18
Q
Where do long-chain omega-3 fatty acids accumulate, where are they active, when are they essential, and where are they found?
A
- DHA is active in the retina of the eye and cerebral cortex of the brain
- ~ half accumulates in human brain before birth
- lipids are essential during pregnancy & lactation for growth and development of the fetus/infant
- EPA and DHA are found in human milk, shellfish, fish/oils, algae
19
Q
What can linoleic acid be elongated into?
A
Linoleic acid can be elongated & desaturated to longer chain Omega-6 FA – Arachidonic acid, C20:4
20
Q
What can linolenic acid be elongated into?
A
α-LnA can be elongated & desaturated to longer chain w3 FA
- Eicosapentaenoic acid, C20:5 (EPA)
- Docosahexaenoic acid, C22:6 (DHA)
21
Q
How does chain length override the effects of saturation?
A
- Chain length overrides the effects of saturation with SFA only
- Expect all lipid sources that are predominantly SFA to be solid at room temperature
- Exceptions are tropical oils: palm oil (C10:0) and coconut oil (C12:0) – both semi-solid at room temperature – firmer than most oils, softer than most animal fat, less likelihood for SC-SFA to pack together due to shorter chain length
22
Q
What are they essential fatty acids?
A
Polyunsaturated fatty acids
- Linoleic acid (Omega-6)
- Alpha-linolenic acid (Omega-3)
23
Q
What are the dietary recommendations for the essential fatty acids?
A
- DRI-AI: recommended EFA intake ratio ~10:1 (Omega-6 : Omega-3)
- Males: 17:1.6 g/day
- Females: 12:1.1 g/day (10.9:1 g/day)
24
Q
Which essential fatty acid do we get a lot of easily, and which do we need to focus on increasing our intake?
A
We typically get a lot of Omega-6 and need to focus on increasing intake of Omega-3
We’re looking for a ratio of about 10:1 (Omega-6:Omega-3)
25
What happens if you heat an oil to its smoke point?
Peroxides form, which can act as free radicals
26
What is the chain length of a short chain fatty acid?
* \<6 carbons in length
* ex., 2C = acetic acid, 3C = propionic acid, 4C = butyric acid
* liquid at room temperature
* SCFA that are 4C in length are found in dairy foods
* SCFA are produced by our gut bacteria as they digest dietary fibre.
27
What is the chain length of a medium-chain fatty acid?
* 6-12C in length
* ex., palm oil (C10:0), coconut oil (C12:0)
* MCFA also found in dairy products
28
What is the chain length of a long-chain fatty acid?
* 14-24C in length
* if SFA, then solid at room temperature (ex., meat)
* if un-SFA, then semi-solid or liquid at room temperature (ex., oleic acid in olive oil (C18:1); alpha-linolenic acid (C18:3) or linoleic acid (C18:2) in canola or camelina oil)
29
How do food manufacturers extend the shelf-life of fat-containing products?
* Fats going rancid is a problem in food manufacturing
* Hydrogenation (partial) of inexpensive plant oils extends the shelf life of fat-containing products (e.g., crackers, cookies)
* Hydrogenation produces **trans FA** and increases the degree of saturation in the FA
* partially hydrogenated oil banned in Canadian food supply, effective fall 2020
30
What is hydrogenation?
* bubble hydrogen gas under pressure using a metal catalyst into inexpensive plant oil (e.g., soybean, corn)
* extends shelf-life by saturating the fatty acids
31
What are the functions of fatty acids?
1. Integrity and fluidity of cell membranes
* FA (as part of phospholipids) provide structural and functional capacity to cell membranes
2. Participate in functionality of the immune system andvision
* Enhanced white blood cell response to foreign substances
* Visual problems with deficiency of essential FA (EFA)
3. Essential FA (EFA) precursors to LC-PUFA
* Conversion to LC-PUFA inefficient (~10%), more efficient to consume LC-PUFA in diet
* EPA, DHA (Omega-3)
* Arachidonic Acid (Omega-6)
4. EFA precursors to EICOSANOIDS
* Hormone-like substances using 20C FA derived from EFA
32
How are eicosanoids derived?
Formed using Omega-6 or Omega-3 essential fatty acids as a precursor.
33
What are the regulatory effects of ecosanoids?
Ecosanoids will have different effects depending on the precursor.
* **Prostaglandins (PG)** – constrict/dilate blood vessels; affect blood pressure – immune assistance – transmission of nerve impulses – smooth muscle contraction, required in childbirth
* **Thromboxanes (TX)** – affect blood clotting
* **Leukotrienes (LK)** – mediators of many inflammatory or hypersensitivity reactions (e.g., asthma)
34
List the six main reasons to consume triglycerides.
1. Fuel source
2. Energy storage
3. Insulation/protection
4. Absorption of fat-soluble vitamins (A, D, E, and K)
5. Satiety
6. Flavour/Texture/Palatability of food
35
Describe the role of triglycerides as a fuel source.
* concentrated source of energy (compared with CHO, PRO)
* Muscles: major fuel at rest and during light-moderate activity
* FA from TG can be mobilized from various sites: blood lipoproteins, adipose, muscle, and dietary fat
* when the body needs energy, hormone-sensitive lipase: inside adipose cells breaks down TG to glycerol & free FA – free FA cross the cell membrane and enter the bloodstream
* albumin (protein) in blood binds to free FA for transport to other cells (e.g., muscle) to be used for energy
* ß-oxidation of FA occurs inside mitochondria of cells
36
Describe the ß-oxidation of fatty acids.
* (occurs inside cells; differs from digestion of dietary fat in small intestine)
* fatty acids broken down into 2C fragments (at ß-carbon)
* each fat fragment (acetyl-CoA) combines with a fragment from the breakdown of GLU (pyruvate -\> oxaloacetate) before being completely oxidized in the TCA cycle (Kreb’s cycle) and electron transport chain to yield energy (ATP), CO2 and H2O
* if adequate CHO is lacking, fat fragments (acetyl-CoA) are not completely oxidized and join together to form ketone bodies
* **“FAT burns in a fire of CHO”**
37
Describe the role of triglycerides as energy storage.
* virtually limitless storage of energy
* non-bulky storage system of energy
* energy-dense @ 9 kcal/g
* mostly stored in adipose tissue
* fat cells increase in size, HYPERTROPHISM, then increase in number, HYPERPLASIA
38
Describe the development of adipose.
* During growth, fat cells increase in number.
* When energy intake exceeds expenditure, fat cells increase in size. **HYPERTROPHISM**
* When fat cells have enlarged and energy intake continues to exceed energy expenditure, fat cells increase in number again. **HYPERPLASIA**
* *With fat loss, the size of the fat cells shrinks, but not the number.*
* Fat cells are capable of increasing their size by 20-fold and their number by several thousand-fold.
39
Describe the role of triglycerides as insulation.
* subcutaneous fat layer (TG) helps insulate against temperature extremes
* acts as a cushion – protects against shock and injury
40
Describe the role of triglycerides regarding satiety and food palatability.
* TG stimulate hormone secretion that delays gastric emptying
* don’t cut too much fat from diet, or lose satiety effect
* many flavours dissolve in fat and improve taste of foods
* smooth, creamy texture (e.g., chocolate, nut butter)
41
Describe the role of triglycerides regarding vitamin absorption.
* FS-vitamins carried with dietary TG for absorption via chylomicrons
* any fat malabsorption condition decreases FS-vitamin absorption
42
List the four main functions of phospholipids.
1. Cell membranes
2. Neurotransmitter
3. Emulsifier
4. Micelle formation during digestion process
43
Describe the role of phospholipids in membranes.
* major structural component of cell membranes
44
Describe the role of phospholipids as neurotransmitters.
* Choline (part of lecithin PL) used with acetyl-CoA to synthesize acetylcholine, required in memory centre of brain
* in later stages of Alzheimer’s disease, see lower activity of enzyme that synthesizes neurotransmitter, acetylcholine
* supplementation with choline or lecithin does not affect memory or progression of disease
45
Describe the role of phospholipids as an emulsifier.
* Amphipathic - can act as emulsifiers of fat
* Lecithin used as emulsifier by food manufacturers to prevent separation of fats and water in products (e.g., chocolate bars, salad dressings)
* **Bile** – body’s emulsifier – contains lecithin (+ bile salts, acids and pigments, cholesterol & water)
46
Describe the role of phospholipids in micelle formation during digestion.
* During digestion of TG and PL, the products, which include: free FA, MG, lyso-PL, as well as cholesterol, fat-soluble vitamins & bile, reach a critical mass and organize to form a micelle
* hydrophobic regions of particles are pulled into the centre
* hydrophilic regions of particles are found on the surface
* Micelles allow the diffusion of larger products of digested dietary lipids across the intestinal cell membrane for further metabolism inside the intestinal cell (bile recycled through distal ileum)
47
Where is bile recycled?
bile recycled through distal ileum
48
What are the main sources of phospholipids?
1. Endogenous Source
* liver can synthesize all the PL the body needs
2. Exogenous Sources
* Food Sources:
* egg yolks, liver
* soybeans, wheat germ, peanuts
* chocolate bars, salad dressings
* Lecithin Supplements - hydrolyzed by lecithinase in small intestine, so very little, if any, gets absorbed intact, adds 9 kcal/g to energy intake - claims: proper cell functioning, healthy cell membranes, better memory
* excessive intake: GI upset, diarrhea, sweating, loss of appetite
49
What is the structure of cholesterol.
* multiple ring structure differs from other 2 categories of lipids
50
Discuss the function of cholesterol as a precursor to vital body compounds.
1. Hormones:
* sex hormones – estrogen, testosterone
* cortisol (stimulates gluconeogenesis during starvation)
2. Vitamin D - critical for calcium and phosphorus absorption
3. Bile:
* water, cholesterol, PL, bile acids/salts/pigments
* liver uses cholesterol to synthesize bile, and stored in gall bladder until needed in small intestine to emulsify dietary lipids
51
Discuss the role of cholesterol regarding cell membrane integrity.
* incorporated as structural component in cell membranes, especially rich in brain, spinal cord and neural cells
* Cholesterol acts as a **bidirectional regulator** of membrane fluidity because at _high temperatures_, *it stabilizes the membrane and raises its melting point*, whereas at _low temperatures_ *it intercalates between the phospholipids and prevents them from clustering together and stiffening.*
52
Discuss the role of cholesterol in the myelin sheath.
* composite of myelin – insulating coating that surrounds axons of nerve cells – facilitates efficient conduction of nerve impulses
53
Is cholesterol beneficial or harmful?
Both!
* there is only ONE molecule called cholesterol
* be careful to note: dietary cholesterol or blood cholesterol
* different transport vehicles (lipoproteins) shuttle cholesterol around in the blood
* how much of each lipoprotein and the location of cholesterol in the body (i.e., in blood, in cells) will determine if cholesterol is beneficial or harmful
54
What are the main sources of cholesterol?
1. Endogenous Sources
* liver can synthesize all the cholesterol the body needs (~800-1500 mg/day compared with average dietary intakes of ~300mg/day)
* liver up- or down- regulates synthesis depending on dietary intake
2. Exogenous Sources
* Food Sources – ANIMAL foods ONLY:
* organ meats ~300mg/100g serving
* 1 large egg yolk ~200mg (none in egg whites)
* lean meats ~90-100mg/100g serving
* fish ~50mg/100g serving
*NOTE: No Supplements exist - thankfully!*
* Read Labels
* be wary of cholesterol-free claims on food products – if it contains no animal fats, then it will be cholesterol-free by default (e.g., peanut butter)
55
Describe the emulsification of fat.
PROCESS:
1. Emulsification - bile from gall bladder
2. Digestion - pancreatic lipase
3. Micelle - formed in lumen
4. Absorption - diffusion
56
How are lipids emulsified prior to digestion?
Bile emulsifies dietary fat (mixed triglycerides)
57
Describe the major hormones and enzymes involved in lipid digestion.
(Lipid digestion occurs mostly in the small intestine)
**Major hormones:**
* Cholecystokinin (CCK) stimulates release of bile from gall bladder into the lumen of the small intestine to emulsify dietary lipids before enzymatic digestion
* Secretin – release of pancreatic juice into small intestine
**Enzymes:**
* pancreatic lipase digests TG MG + 2 free FA
* lyso-phospholipase digests 1 FA from phospholipids (PL)
* cholesterol remains intact, FA hydrolyzed from cholesteryl ester
58
What are small products of fat digestion?
* Glycerol
* Short Chain Fatty Acids
* Medium Chain Fatty Acids
* up to 12C
59
How are small products of fat digestion absorbed?
Absorbed via diffusion and transported to the liver.
60
What are large products of fat digestion?
* PL, lyso-PL = Phospholipids
* F/S = Fat-soluble vitamins
* LCFA = Long Chain Fatty Acids
* MG = monoglycerides
* 14C +
61
How are large products of fat digestion absorbed?
* Micelle forms and diffuses across membrane.
* Inside intestinal cells triglycerides and phospholipids are remade (+ proteins)
* Chylomicrons exit to lymph
62
Discuss the absorption of dietary lipids.
* SCFA, MCFA, glycerol diffuse into intestinal cells unassisted, and leave by entering directly into the bloodstream to portal vein
* LCFA, MG, lyso-PL, PL, dietary cholesterol, F/S vitamins, and bile form a MICELLE for diffusion of the lipids into intestinal cells
* micelles are water-soluble structures to carry non-water-soluble fats into the intestinal cells via diffusion (bile not absorbed here)
* once inside intestinal cells, TG & PL are re-formed then packaged along with proteins synthesized in the intestinal cells and intact cholesterol to form a CHYLOMICRON
* chylomicrons are soluble in water and diffuse out of intestinal cells into lymph (aqueous environment) and eventually enter into the bloodstream at the thoracic duct into the subclavian vein
63
How to chylomicrons enter the blood stream via lymph?
* chylomicrons are soluble in water and diffuse out of intestinal cells into lymph (aqueous environment) and eventually enter into the bloodstream at the thoracic duct into the subclavian vein
64
Discuss the composition of a lipoprotein.
* protein and phospholipid shell (hydrophilic)
* fats (cholesterol, PL,TG, fat-soluble vitamins) in core (hydrophobic)
65
What type of lipoprotein are chylomicrons?
Dietary lipids
66
What type of lipoprotein are VLDL, LDL, and HDL?
Non-dietary (endogenous) lipids
67
What is the source, composition, and function of chylomicrons?
**Source**: Formed in intestine
**Composition**: mainly triglycerides
**Function**: Transports dietary fat in the lymph, then in the blood to the cells first, and lastly to the liver where it is removed from circulation as a chylomicron remnant
68
What is the source, composition, and function of VLDL?
**Source**: Formed in liver
**Composition**: mostly triglycerides
**Function**: Transports lipids produced in liver and arriving at liver in chylomicron remnants to cells
69
What is the source, composition, and function of LDL?
**Source**: Formed from VLDL
**Composition**: mostly cholesterol
**Function**: Transports endogenous cholesterol from liver to peripheral tissues
70
What is the source, composition, and function of HDL?
**Source**: Formed in liver, intestine
**Composition**: mostly protein
**Function**: Reverse transport of cholesterol from artery walls, cells, and other lipoproteins to the liver for disposal
71
Describe the relationship of LDL and development of atherosclerotic plaque.
72
What are the desired ratios of blood levels of lipids?
Desired LDL : HDL ratio = between 4.5–5 : 1
73
What are the physiological effects of all the different dietary lipids?
74
Where can lipids be found in foods?
75
Why are plant sterols promoted?
Plant sterols promoted to:
* reduce dietary cholesterol absorption
* exert strong anti- inflammatory effects
* result in smaller lesions in arteries (mice model)
* affect gene expression
* Levels at 2% of total caloric intake have produced cardioprotective effects.
76
What are the DRI: Acceptable Macronutrient Distribution Range (AMDR) and absolute values (RDA/AI) for dietary lipids?
NOTE: There is no DRI recommended intake for trans FA, SFA, or dietary cholesterol
77
What are the typical fat intakes in the Canadian diet?
* PUFA: more linoleic (w-6 FA) than linolenic (w-3 FA)
* Goal: increase ratio of w-3 PUFA : w-6 PUFA
78
What are some messages from the Canadian Food Guide regarding lipids?
* Choose vegetables and fruit prepared with little or no added fat, sugar or salt
* Choose grain products that are lower in fat, sugar or salt
* Drink skim, 1% or 2% milk each day
* Select lower fat milk alternatives
* Have meat alternatives such as beans, lentils and tofu often
* Eat at least two Food Guide servings of fish each week
* Select lean meat and alternatives prepared with little or no added fat or salt
* Include a small amount of unsaturated fat each day
* Limit foods and beverages high in calories, fat, sugar or salt
79
What are general health guidelines regarding lipids?
* Reduce dietary cholesterol to ≤300 mg/day
* Reduce total fat intake to \<30% of caloric intake
* Keep SFA fat intake to \<7-10% of caloric intake
* Keep PUFA fat intake to ~10% of caloric intake
* Keep MUFA fat intake to ~10-15% of caloric intake § Aim for 1:1:1 or 1:1.5:1 ratio of P:M:S fatty acids
* Consume ~25-35 g dietary fibre/day
* Have blood pressure checked regularly
80
How do food labels address lipids?
Canadian Nutrition Facts Table lists total, saturated, and trans fat content per serving
81
What are dietary recommendations regarding dietary lipid intake when eating out?
* Choose grilled, broiled or stir-fried entrees
* Choose foods prepared with little or no fat
* Take home part of larger portions
* Ask for sauces on the side so you can use a smaller amount
82
What are lifestyle changes that benefit health effects related to fat intake?
* Follow dietary guidelines for fat intake
* Be physically active to HDL and blood TG
* Maintain a healthy body weight
83
How do you improve your dietary fat proportion intake?
* Include more MUFA (Omega-9) and Omega-3 (vs. Omega-6) PUFA
* Reduce SFA and trans FA
