CHAPTER 6

LIPIDS

LEARNING OUTCOMES

• Explain the basic chemical structure of fatty acids and how they are named• Describe the functions of triglycerides, fatty acids,

phospholipids and sterols in the body• Classify and evaluate the different fatty acids based

on their health benefits or consequences• Identify food sources of triglycerides, fatty acids,

phospholipids and sterols

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LEARNING OUTCOMES

• Describe the recommended intake of lipids• Identify strategies for modifying total fat, saturated

fat, and trans fatty acids intake• Explain the digestion, absorption and transport of

lipids in the body• Discuss health concerns related to dietary fat intake• Describe dietary measures to reduce the risk of

developing cardiovascular disease

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TRIGLYCERIDES

• Most common lipid in food and the body• Make up 95% of what

we eat and what is in our bodies• FA can all be the same

or all be different, the fatty acids are long chains of carbons with hydrogens attached

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FUNCTIONS OF TRIGLYCERIDES

• Provide energy• Provide compact energy source• Insulate and protect the body• Aid fat-soluble vitamin absorption and

transport• Essential fatty acid functions

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FOOD SOURCES OF TRIGLYCERIDES

• Fruits and Vegetables• Low fat except avocados and coconuts

• Dairy• Low fat products are available

• Grains• Low-fat except when fat is added e.g. pastries, pancakes

• Fats• Usually a combination of many-described by the

predominate fat

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STRUCTURE

• Esterification• Joining 3 fatty acids to a glycerol unit

• De-esterification• Release of fatty acids-results in free fatty acids

• Diglyceride• Loss of one fatty acid

• Monoglyceride• Loss of two fatty acids

• Re-esterification• Reattaching a fatty acid to a glycerol that has lost a fatty acid

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CARBON CHAIN LENGTH

• Long chain fatty acids• 12 or more carbons (ex. Beef, lamb, plant oils)

• Medium chain fatty acids• 6-10 carbons (ex. coconut and palm oils)

• Short chain fatty acids• Less than 6 carbons (ex. dairy products)

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SATURATION

Each molecule wants to form as many bonds as it can•Carbon- 4•Oxygen- 2•Hydrogen-1

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SATURATION

• Saturated fatty acids• This 18 carbon fatty acid is fully saturated with hydrogen

atoms.• No double bonds• Increase blood levels of cholesterol• Example: red meat, high fat dairy, coconut and palm oil- solid at

room temperature.

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SATURATION

• Monounsaturated fatty acids• One double bond• Decrease blood levels of cholesterol• Example: olive oil, canola oil, peanut oil

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SATURATION

• Polyunsaturated fatty acids• Many double bonds (at least 2)• Decrease blood levels of cholesterol• Example: Vegetable oils and fish oil

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SHAPE

• Cis fatty acids• Bent carbon chain

• Trans fatty acids• Straight carbon chain• Hydrogenation: Adding

hydrogen to make an unsaturated fat more saturated-yields: trans fatty acids

• Solidifies the lipid, increases shelf life of product (tub margarine, baked goods)

• Increases cholesterol even more than saturated fat

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TRANS FATS

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TRANS FATS

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1902- Scientist Wilhelm Normann finds that liquid oils can be hydrogenated to form trans fatty acids. 

1911- Procter & Gamble introduces Crisco vegetable shortening in grocery stores. 

1937- As World War II progresses, the use of margarine (yellow colored vegetable shortening) rises sharply due to butter rationing.

1984- Consumer advocacy groups campaign against using saturated fat for frying in fast-food restaurants. In response, most fast-food companies begin using partially hydrogenated oils containing trans fat instead of beef tallow and tropical oils high in saturated fats.

TRANS FATS

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1990s there were several studies correlating trans fatty acids and increased LDL (bad) cholesterol levels and a higher incidence of heart disease. 

1993- Health advocacy groups call for fast-food restaurants to stop using partially hydrogenated oils in their deep fryers.

1999- The U.S. government proposes a law requiring food manufacturers to list trans fat amounts on nutrition labels.  The proposal is not passed as law.

TRANS FATS

2002- The government agrees with researchers for the first time on record: that there is likely no safe level of trans fat and that people should eat as little as possible.

2003- The FDA passes a law requiring that trans fat be listed on the Nutrition Facts label on food products; food manufacturers have three years to comply. 

2006- Trans fat labeling becomes mandatory in the United States. 

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SHOULD TRANS FATS BE LEGAL?

Illegal•Denmark, 2003•Banned in almost all foods•Heart disease has fallen by 20% between 2001 (before the ban) and 2006 (two years after the ban)

•NY City, 2006•Restaurants/food service establishments

•Switzerland, 2008•Banned in almost all foods

Legal or limited•Some restrict the amount of trans fat in foods (Canada, Boston)•Others mandate labeling•Others have no laws concerning trans fat

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TRANS FAT LABELING LOOPHOLE

Any food that contains 0.5 grams or less of trans fat can be listed as zero grams on the Nutrition

Facts label. It may seem like a small amount, but there is no safe amount and all those half grams

can add up.

You must read the ingredients label: “partially hydrogenated” is in the list, it is a food that contains trans fats and should be avoided.

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NAMING FATTY ACIDS(OMEGA AND DELTA)

• Omega System• Double bond closest to omega (methyl) end• Omega-3 fatty acid is 18:3 ω3• Omega-6 is 18:2 ω6

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OMEGA 6 AND OMEGA 3 FATTY ACIDS

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Eicosanoid “Local hormone”

TWO ESSENTIAL FATTY ACIDS

Alpha-linolenic (Omega-3)•Polyunsaturated•Major source of Omega 3 fatty acids in foods•Used to make EPA and DHA and Eicosanoids

Linoleic (Omega-6)•Polyunsaturated•Major source of Omega 6 fatty acids in foods•Used to make Arachidonic acid, and Eicosanoids

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TWO ESSENTIAL FATTY ACIDS

• Alpha-linolenic• Cold water fish (salmon,

tuna, sardines), walnuts, flax, canola oil• Reduces inflammation,

thins blood, and reduces plasma triglycerides

• Linoleic• Beef, poultry, safflower

oil, sunflower oil, corn oil, mayonnaise• Regulates blood

pressure, can increase blood clotting and inflammation

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ESSENTIAL FATTY ACID NEEDS

• Body unable to synthesize so Adequate Intake has been established• Approximately 2-4 Tablespoons daily• Omega 6 intake usually high, Omega 3 intake usually

too low-this in balance has health consequences• Deficiency• Unlikely• Could result in slowed growth, flaky and dry skin,

delayed wound healing• Toxicity• No upper level set

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3 soft gels=900mg of DHA + EPA

500 mg as ALA 32 mg DHA

3000 mg of DHA+EPA in 6oz

AHA1000mg of DHA + EPA = 2 servings of fish/week

Alpha linolenic acid ALA (flax, mayo), lower cholesterol but no relationship w/heart disease and may increase risk of prostrate cancer

DIETARY FATS

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DIETARY FAT RECOMMENDATIONS

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AMERICAN HEART ASSOCIATION RECOMMENDATIONS

• Limit saturated fats to 10% of total calories• Limit polyunsaturated fats to 10% of total

calories•Minimize trans fat intake• Limit cholesterol intake to less than 300 mg• Eat at least two servings of fatty fish/week

(tuna, salmon, mackerel, lake trout, herring, and sardines)

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FAT INTAKE

•North American fat intake has doubled in the last century• Too high• Saturated fat, trans fat, Omega 6

• Too low• Omega 3

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MEDITERRANEAN DIET

• Up to 40% fat if comprised of monounsaturated fatty acids• Diet is high in• Olive oil, fruits, vegetables, whole grains, beans, nuts

and seeds• Small to moderate amounts of cheese, yogurt and

fish

• Limit eggs and red meat• Exercise

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MEDITERRANEAN DIET

• Breakfast: Greek yogurt topped with berries and walnuts; Coffee or teaLunch: Lentil soup with swish chard topped with taziki sauce; hummus and pitaSnack: Whole grain crackers and cheeseDinner: Roasted cod paired with a wheat berry salad consisting of olive oil vinaigrette, feta, parsley, and tomatoes and a glass of red wineDessert: Fresh fruit drizzled with honey

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FAT REPLACEMENTS

•Water, Protein, Air (soft serve ice cream)• Carbohydrates• Fiber (Ztrim)• Corn syrups, syrup solids, and high-fructose corn

syrups are used as fat replacers in many fat-free and reduced-fat cookies

• Engineered fats• Olestra (Lays's Light, Ruffles Light, Doritos Light,

and Tostitos Light)

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OLESTRA

• Olestra is synthesized from sucrose, it can bond with six, seven, or eight fatty acids, making it too large and irregular to move through the intestinal wall and be absorbed.

• Because olestra is undigested, it inhibits absorption of fat soluble vitamins (fun side effects of this!)

• FDA requires manufacturers to add vitamins A, D, E and K to products made with olestra to counter that effect.

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PHOSPHOLIPIDS

• Hydrophobic and Hydrophilic Ends• Functions• Component of cell

membranes• Emulsifier

• Sources• Synthesized by the body• Food: lecithin in egg yolks,

wheat germ and peanuts

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PHOSPHOLIPIDS

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STEROLS

• Ring structure, most known is cholesterol• Plant sterols block cholesterol absorption sites in the human

intestine, thus helping to reduce cholesterol in humans, but there is some concern that they may block absorption of other important nutrients as well• Functions• Steroid hormones, bile, cell membranes, chylomicrons

• Sources• Synthesized by the body• Food: animal origin (meat, fish, eggs, dairy)• Food additive: Benecol and Take Control

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STEROLS NEEDED TO MAKE STEROID HORMONES

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FAT DIGESTION

• Stomach• Gastric lipase • Triglycerides are broken down into monoglycerides and

free fatty acids

• Liver-makes bile• Gall bladder • CCK triggers bile release from gall bladder

• Pancreas • Pancreatic lipase, phospholipase, cholesterol lipase

into common bile duct, which empties to SI

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FAT DIGESTION

• Small Intestine• Bile emulsifies fat to form micelles (acted upon

by pancreatic lipase)• Phospholipids are broken down into free fatty

acids, glycerol and phosphoric acid by enzymes from the SI and pancreas• Cholesterol esters are broken down into

cholesterol and free fatty acids by enzymes from SI and pancreas• Most digestion in duodenum and ileum

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FAT DIGESTION

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Bile emulsifies fat: breaks it into tiny

droplets called micelles (keeps the fat suspended in the

water-based intestinal contents

FAT ABSORPTION

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FAT ABSORPTION

• The lipid portion of micelles is absorbed by the brush border of the absorptive cells in the duodenum and jejunum• Short and medium chain fatty acids are absorbed via the

portal vein• Long chain fatty acids are re-esterified and enter the

lymphatic system• Bile is recycled via enterohepatic circulation

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TRANSPORTING FAT

• Transporting fat through water based blood and lymphatic system is a challenge• Short and medium chain fatty acids travel via

cardiovascular system to liver• Long chain enter lymph system

• Fat is transported lipoproteins• Lipid core• Shell composed of protein, phospholipid and cholesterol

that allow transportation

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TYPES OF LIPOPROTEINS

• Chylomicrons• Transport of dietary triglycerides from small intestine to

cells• VLDL• Carries mainly triglycerides from liver to cells

• LDL• Made mostly of cholesterol, carries cholesterol to cells

• HDL• Made mostly of protein, pick up and recycle or dispose of

cholesterol

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TYPES OF LIPOPROTEINS

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PATHWAYS FOR CHOLESTEROL UPTAKE

• Receptor Pathway• LDL is removed from

blood by cells via the LDL receptor• In cells the LDL is broken

down and utilized in the body (to do what?)• Excess builds up and

becomes oxidized

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PATHWAYS FOR CHOLESTEROL UPTAKE

High Density Lipoproteins (HDL or good cholesterol)• How does it get its name?• Picks up cholesterol

throughout the body-eventually this leads to excretion of LDL• Blocks oxidation of LDL

“Scavenger” WBC embed in blood vessels and engulf and digest LDL •Can build up over time-plague develops (what is this called?)

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ATHEROSCLEROSIS

• What can you do to prevent plaque buildup?

• What do cholesterol lowering medications do?

• How can you remove an existing plaque to prevent heart attack and stroke?

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CARDIOVASCULAR DISEASE (CVD)

• Development of CVD• Atherosclerotic plaque forms• Result: Heart attack and stroke• Risk factors• Cannot change age, gender, race and genetics• Can change blood triglyceride and cholesterol

levels, hypertension, smoking, physical inactivity, obesity, diabetes and other diseases

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BLOOD LIPOPROTEIN LEVELS

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PREVENTING CVD (LIMIT)

• Total fat 20-35% total calories• Saturated fat < 7 % total calories• Trans fat low• Polyunsaturated < 10% total calories•Monounsaturated < 20% total calories• Cholesterol < 200 mg daily

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PREVENTING CVD (EMPHASIZE)

• Include 2 grams plant stanols/sterols• Soluble fiber 20-30 g• Eat fatty fish 2x/week• Keep body weight at a healthy level• Increase physical activity• Do things to increase your HDL (exercise)• Eat foods that prevent oxidation

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PREVENTING CVD

• Nuts• “scientific evidence suggests but does not prove that eating

1.5 oz of nuts/day as part of a diet low in saturated fat and cholesterol may reduce risk of heart disease.” (almonds, hazelnuts, peanuts, pecans, some pine nuts, pistachio nuts and walnuts)

• Serving sizes: 1.5 oz is ~ 40 unshelled nuts, 1/3 cup, or 1 large handful

• Nutrition info for 1.5 oz almonds: 250 kcal, 9 grams protein, 5 grams fiber, 1.5 grams sat fat, 13.5 g mono fat, 50% of Vit E needs, and magnesium, riboflavin, copper, phosphorus

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PREVENTING CVD

• Supplements • B vitamins like folic acid, B12, and B6 (homocysteine?)• Niacin or Vitamin B3 (raise HDL?)• Vitamin E (antioxidant), may prevent but NOT treat• Garlic (lower cholesterol, less clumping of platelets,

antioxidant) • Fish oil (omega 3, DHA + EPA)- AHA advises 1000 mg of

DHA +EPA for those who have heart disease

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HEALTH CONCERNS

• Dangers of low fat diet?• High polyunsaturated fat intake• Excessive omega 3 fat intake• Imbalances in omega 3 and omega 6 fats• Diets high in trans fats• Diets high in total fat

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MAKING RECOMMENDATIONS

• Breakfast: Everything Bagel w/cream cheese, coffee w/cream and sugar• Lunch: 12 inch Italian sub,

Diet Coke, Baked Lays• Snack: Quaker Granola bar• Dinner: Easy Mac w/hotdogs• Snack: Ice cream

• Changes if you were normal weight but have high cholesterol• Changes if you

were interested in Mediterranean diet

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