functions of lipids
TRANSCRIPT
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This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike License. Your use of this material constitutes acceptance of that license and the conditions of use of materials on this site.
Copyright 2006, The Johns Hopkins University and Benjamin Caballero. All rights reserved. Use of these materials permitted only in accordance with license rights granted. Materials provided “AS IS”; no representations or warranties provided. User assumes all responsibility for use, and all liability related thereto, and must independently review all materials for accuracy and efficacy. May contain materials owned by others. User is responsible for obtaining permissions for use from third parties as needed.
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Lipids
Benjamin Caballero, MD, PhDJohns Hopkins University
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Section A
Definitions
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Some Definitions
Lipids —Generic name, may include lipoproteins, phospholipids, etc.Fats —Also a generic name, but applied mostly to fats that are solid at room temperatureOils—Liquid at room temperatureFatty Acids—Basic building blocks for fatsTriglycerides—Esters of fatty acids with glycerol (may also be mono- or di-glyceride)
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Fatty Acids
COOH
[ C
C
C
C
C
] nH2
H2
H2
H2
H3
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Fatty Acids
COOH
[ C
C
C
C
C
] nH2
H2
H2
H2
H3
Carboxyl end∆ numbering system
Methyl endn ( ω ) numbering system
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Glycerides
H2
H2
H2
HO-C
HO-C
HO-C
Glycerol
C -C -[C -C -CO-O-C
C -C -[C -C -CO-O-C
C -C -[C -C -CO-O-C
Triglyceride
H2
H2
H2
H3
H3
H3
H2
H2
H2
H2
H2
H2
H2
H2
H2
]n
]n
]n
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Other Lipids
Phospholipids− Phosphatidylcholine− Phosphatidylethanolamine
Sphingolipids, glycolipidsSterols− Sex hormones− Cholesterol− Bile acids
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Unsaturated Fatty Acids
COOH
[ C
CH
CH
C
C
] nH2
H2
H3 Methyl endn ( ω ) numbering system
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Structural Notation
COOH
C
COOHC
Palmitic acid, 16:0
Oleic acid, 18:1, n-9
2 4 6 8 10 12 14 16
13 5 7 9 11 13 15
2 4 6 8 11 13 15 17
13 5 7 9 10 12 14 16 18
H3
H3
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Functions
Energy storage, mobilization, and utilizationProstaglandin, cytokine synthesisCell differentiation and growthCell membrane structure, myelinationSignal transmissionHormone synthesisBile acid synthesis
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Essential Fatty Acids
Humans cannot synthesize double bonds within the last nine carbons of the methyl end (n) of any fatty acid chainFatty acids with double bonds in those locations must therefore come from the diet—and are considered essentialThus, EFA are (poly)unsaturated− There are no essential saturated fats
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Essential Fatty Acids
Only two fatty acids are essential:− Linoleic and alpha-linolenic acids (ALA)
Both are (poly)unsaturatedTherefore, absolute requirements for fat in the diet applies only to unsaturated fat
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Linoleic Acid: Cottonseed, Sunflower, Soybean, Corn
C18:2, n-6,9
COOH
C
2 4 6 8 10 12 14 16
3 5 7 9 11 13 15 17
18
H3
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Alpha-Linolenic Acid: Soybean, Mustard, Linseed, Walnut
C18:3, n-3,6,9
COOH
C
2 4 6 8 10 12 14 16
3 5 7 9 11 13 15 17
18
H3
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Each EFA Heads a Powerful Family
18:3, n-3 (ALA)
20:5, n-3 Eicosapentaenoic (EPA)
22:5, n-3 Docosapentaenoic (DPA)
22:6, n-3 Docosahexaenoic (DHA)
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Each EFA Heads a Powerful Family
18:3, n-3 (ALA)
20:5, n-3 Eicosapentaenoic (EPA)
22:5, n-3 Docosapentaenoic (DPA)
22:6, n-3 Docosahexaenoic (DHA)
18:2, n-6 (Linoleic)
20:4, n-6Arachidonic acid (AA)
ProstaglandinsLeukotrienes
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Trans- Fatty Acids
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Trans- Fatty Acids
Naturally present in small amounts (<1% of total calories) in animal food sources, including human milkMainly introduced in the food chain by the industrial process of hydrogenationThis process is used to make oils solid at room temperature
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Composition of Some Edible Oils
% 16:0 18:0 18:1 18:2n6 18:3n3
Olive 12 2 72 11 1
Palm 42 4 43 8 0
Canola 5 1 56 24 10
Sunflower 6 6 33 53 0
Butter 28 16 26 1 2
Beef 28 13 43 2 1
Chicken 27 7 41 14 1
Salmon* 19 4 23 1 1
*EPA=8%, DHA=11%
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Section B
Fat Metabolism
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Overview of Fat Metabolism
Modern Nutrition in Health & Disease 10th Ed.
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Key Lipid Molecules 1
Chylomicrons− Formed in the intestine to carry fatty acids into the
circulation after a meal is consumed− Disappear from the blood in the fasting state, degraded
in the liverVLD− TG-rich lipoprotein made in the liver− Releases TG to tissues and give origin to LDL
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Key Lipid Molecules 2
LDL− Cholesterol-rich lipoprotein made from remnant VLDL,
carries about 70% of blood cholesterolHDL− Made both in liver and intestine, carries cholesterol from
the periphery to the liverAll lipoproteins are eventually captured and degraded in the liver via a receptor system
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Section C
Recommendations and Guidelines
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Fat in the Human Diet
Fat is an efficient way to pack more calories in less volume and, thus, fat is important for feeding infants and young childrenAfter the first year of life, there is no particular advantage in using fat to provide caloriesHowever, flavor and texture of foods are highly dependent on their fat content
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Total Fat: Infants and Children
Infants fed breast milk consume 50% fatAfter weaning, they should progressively reach the recommended fat intake level for adults, by age 8-10
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Total Fat: Adults
From 20% to 35% of total calories can be derived from fat
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Total Fat: Adults
From 20% to 35% of total calories can be derived from fat Lower limit is set by altered blood lipids ( TG, LDL)
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Total Fat: Adults
From 20% to 35% of total calories can be derived from fat Lower limit is set by altered blood lipids ( TG, LDL)Upper limit is determined by increasing risk of excess energy intake and obesity
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Recommended Intake: Saturated Fat
There is no physiological need for saturated fat; however, it isvirtually impossible to create a healthy saturated fat-free dietThus, the recommendation is to consume no more than 10% of total calories from saturated fatAlso, some fat in the diet is needed to allow absorption of fat-soluble vitamins
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Recommended Intake: Unsaturated Fat
Essential Fatty AcidsLinoleic acid—5-10% of total caloriesAlpha-Linolenic acid—0.2-1.2% of total caloriesDiet should contain certain amount of preformed PUFAs (DHA, EPA)− This can be achieved by consuming fatty fish twice a
week
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EFA Deficiency
Clinical− Dermatitis− Thrombocytopenia− Increased susceptibility to infections− Failure to thrive− History of low fat intake
Laboratory− Serum Triene:Tetraene ratio > 0.4
Copyright 2005, Benjamin Caballero and The Johns Hopkins University. All rights reserved. Use of these materials permitted only in accordance with license rights granted. Materials provided “AS IS”; no representations or warranties provided. User assumes all responsibility for use, and all liability related thereto, and must independently review all materials for accuracy and efficacy. May contain materials owned by others. User is responsible for obtaining permissions for use from third parties as needed.