Lipids Flashcards
1
Q
Lipid
Characteristics
A
Triacylglycerols, phospholipids, and cholesterol.
Caloric content mainly in fatty acids.
Metabolized to acetyl CoA to generate ATP.
Nutritionally categorized into 3 groups:
-
Saturated (SAT)
- warm blooded animals
- Monounsaturated (MUFA)
-
Polyunsaturated (PUFA)
- plants grown in cooler climates
- cold water fish
2
Q
Trans Fatty Acids
A
-
Sources:
- Modest amount in meat and dairy products due to bacterial fermentation
- Significant amount in partially hydrogenated oils (PHOs)
- Formed via catalytic hydrogenation of polyunsaturated vegetable oils
- Baked and fried foods
-
Effects:
- ↑ plasma cholesterol
- ↑ LDL
- ↓ HDL
- ↑ risk of CAD
3
Q
Essential Fatty Acids
A
Linoleic acid (18:2 𝜔-6)
𝛼-Linolenic (18:3 𝜔-3)
-
Dietary recommendations:
- EFAs should be ≥ 1% total energy
-
During pregnancy or lactation, ≥ 3% total energy (3 en%)
- Especially 𝛼-Linolenic (18:3 𝜔-3)
- Accounts for most of the EFAs in brain
- Further desaturation and elongation forms:
- arachidonic acid
- eicosapentaenoic acid (EPA)
- docosahexaenoic acid (DHA)
4
Q
Essential Fatty Acid (EFA)
Deficiency
A
All cells require EFAs for proper function.
Deficiency results in numerous symptoms including scaly and dry skin.
Condition quite rare.
Normally, EFA → eicosanoids (20:4) ⇒ a tetraene.
With deficiency, oleate → closest product (20:3 𝜔-9) ⇒ a triene.
Triene/Tetraene ratio above 0.2 suggestive of EFA deficiency.
EFA deficiency associated with:
-
geriatric patients with poor diets
- especially those with PAD
-
fat malabsorption syndromes
- especially after surgical bowel resections
- prolonged parenteral alimentation when formula EFA deficient
5
Q
Dietary Lipids
A
-
Triglycerides are 90% of dietary lipids
- digestion/absorption virtually complete
-
Phospholipids important for digestive process
- some secreted in bile along with bile acids
-
Sterols tag along
- RDA < 300 mg/day
- normal intake 200-600 mg/day
- digestion/absorption incomplete
- endogenous secreted in bile
6
Q
Lipid Digestion
A
-
Lingual lipase (oral phase) and gastric esterases (gastric phase) start digestion.
- Active at low pH of the stomach
- Minimal in newborns due to poor gastric acid secretion
- Minimal effect on LCFA esters
- Active at low pH of the stomach
-
Intestinal lipolysis ⇒ hydrolysis of fatty acid esters
-
Triglycerides → FFA + diglycerides → monoglycerides (2-MG) + FFA
-
Pancreatic lipase + colipase mainly
- Colipase binds lipase + TAG droplet
- Displaces bile salts + phospholipids
- Allows lipase to work at max rate
- Intestinal lipases help
- Max activity @ pH > 7
-
Pancreatic lipase + colipase mainly
-
Phospholipids → FFA + other products
- Phospholipase
-
Cholesteryl oleate → cholesterol + oleic acid
-
Esterase (Cholesterol ester hydrolase)
- Activated by bile salts
-
Esterase (Cholesterol ester hydrolase)
-
Triglycerides → FFA + diglycerides → monoglycerides (2-MG) + FFA
- Bile salts, phospholipids, FFA, 2-MG, sterols, and other lipids incorporated into mixed micelles.
- Mixed micelles brought to enterocytes for absorption.
7
Q
Lipid Absorption
A
- Mixed micelles brought to enterocytes
- SCFA and MCFA absorbed directly into blood via portal vein
- LCFA + apolipoprotins form chylomicrons
- Chylomicrons absorbed via intestinal lymphatics ⇒ thoracic duct
- Transported in the blood as part of plasma lipoproteins
- Chylomicrons, VLDL, LDL, HDL
8
Q
Sterol Absorption
A
-
Cholesterol esters must be de-esterified by pancreactic cholesterol esterase to be absorbed
- Includes dietary sterols and endogenous cholesterol from bile
- Rate of hydrolysis much less than TAGs
-
Intestinal free sterols (mainly cholesterol) only absorbed after solubilization in bile salt micelles
- Overall absorption incomplete
- 2/3 dietary cholesterol excreted in feces
- Increased dietary intake ⇒ ↑ plasma cholesterol levels
- large individual variation
- Unexplained specificity of sterol absorption
- only ~ 5% of plant sterols absorbed (ex. 𝛽-sitosterol)
- high intake of dietary plant sterols interferes with cholesterol absorption
9
Q
𝛽-sitosterolemia
A
- Rare genetic storage disease
- ~ 1/3 dietary sitosterols are absorbed (plant sterol)
- 𝛽-sitosterol deposits found in many tissues & tendon xanthomas
- plasma cholesterol levels normal
10
Q
Malabsorption Syndromes
A
Effects:
- Serious nutritional consequences
- Fat-soluble vitamin deficiency
- Steatorrhea
-
Interferes with divalent cation absorption (Ca2+, Mg2+, Zn2+)
- unabsorbed fat digestion products form metal soaps with cations
- because Ca2+ bound to FAs, plant oxalate absorption ↑
- major source of kidney stones
Treatment
- Remove most dietary fats
- Replace with medium chain triglycerides (MCT)
- more readily digested
- can be absorbed without hydrolysis by pancreatic lipase
- lipolysis releases octanoic and decanoic acids (C8/C10)
- absorbed directly via portal vein
- improves absorption efficiency
11
Q
Causes of Steatorrhea
A
- Pancreatic disease
-
Insufficient bile
- gallbladder or cystic duct obstruction
- liver dysfunction
- Loss of large segments of small intestine
-
Damage to intestinal villae
- Celiac disease
- (non-tropical) Sprue
-
Failure to synthesize chylomicrons
- Abetalipoproteinemia (rare)
12
Q
Celiac Disease
A
-
Fragment of gluten resistent to proteolytic degradation
- found in wheat, oats, and rye but not rice or corn
- Autoimmune response leads to destruction of intestinal villous structure
- Common disorder
- prevalent in Caucasians and East Asians
- 72-hour fecal fat test used for dx
-
Symptoms include:
- deficiency of lipid soluble proteins
- steatorrhea
- lactose intolerance
- hypocalcemia
- weight loss
13
Q
Cystic Fibrosis
&
Malabsorption
A
- Cystic fibrosis results in impaired salt and water transport due to CFTR channal dysfunction
-
Secondary conditions include:
-
Exocrine pancreatic insufficiency (PI) in 90% of CF patients
- Results in subsequent fat malabsorption by 1 year of age
- Detected by:
- 72-hr fecal fat balance study
- fecal elastase immunosorbent assay
- CF-related diabetes (CFRD)
- distal intestinal obstruction syndrome (DIOS)
-
various hepatobiliary diseases
- cholelithiasis
- fibrosis
- cirrhosis
-
Exocrine pancreatic insufficiency (PI) in 90% of CF patients
-
Nutritional considerations:
- pancreatic enzyme replacement therapy (PERT)
- attempts to stimulate pancreatic enzyme release
-
lipase deficiency of > 10% normal results in fat-soluble vitamin malabsorption
- steatorrhea
- poor growth
- may require gastrostomy tubes for feeding
- nutritional conseling
- caloric intake of 120-150% of normal for age and gender
- 40% of diet from fat intake
- female CF patients with PI have increased BEE during puberty
- requires special nutritional attention
- pancreatic enzyme replacement therapy (PERT)
14
Q
Fats & Atherosclerosis
A
-
↑ dietary fat and cholesterol ⇒ ↑ atherosclerosis
- dietary fat most important
- main source of cholesterol synthesized from FA metabolites not dietary sterols
- foods with high cholesterol but low fat have little effect on lipid profile (ex. shrimp)
- dietary fat most important
-
Manifestations of diet effect
- ∆ lipoprotein profile
- ↑ LDL & ↓ HDL
- ∆ susceptibility to thrombosis
- ∆ lipoprotein profile
-
Effects on fatty acid composition by dietary fats:
- SAT & trans-unsaturated FA more atherogenic
-
PUFA & MUFA (mainly oleic acid) less atherogenic
- diets analyzed via P/S ratio (PUFA:SAT)
- 𝜔-3 PUFA (fish oils) most antiatherogenic
15
Q
American Heart Association
Dietary Recommendations
A
-
Overall healthy eating pattern
- balanced diet from all major food groups
- more fruits, vegetables, grains
- fish > meat
- Healthy body weight
-
Desirable cholesterol level
- total blood cholesterol > 200 mg/dl risk factor for CAD
- total blood cholesterol > 240 mg/dl requires vigorous intervention
- Desirable BP level
-
Limit trans fats
- hard margarines worse than soft
AHA does not recommend antioxidant supplements, very low fat diets, or 𝜔-3 supplements currently.
