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5Lipids: Essential

Energy-Supplying Nutrients

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What Are Lipids?

• Lipids• Diverse group of molecules that are insoluble in

water

• Fats• The lipid content of diets and foods

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What Are Lipids?

• Three types of lipids are found in foods and in body cells and tissues:• Triglycerides• Phospholipids• Sterols

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Triglycerides

• Triglycerides (triacylglycerides) contain:• Three fatty acid molecules• One glycerol molecule

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Triglycerides

• Fatty acids are classified by: • Carbon chain length• Saturation level• Shape

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Triglycerides: Chain Length

• Short-, medium-, or long-chain fatty acids• Carbons can be numbered• Carboxyl end (COOH): -carbon (alpha—first)

• Methyl end (CH3): Ω-carbon (omega—last)

• Determines method of lipid digestion, absorption, metabolism, and use

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© 2011 Pearson Education, Inc.

Triglycerides: Saturation

• Saturated fatty acids have hydrogen atoms surrounding every carbon in the chain

• Monounsaturated fatty acids lack one hydrogen atom (one double bond)

• Polyunsaturated fatty acids have more than one double bond

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© 2011 Pearson Education, Inc.

Triglycerides: Shape

• Determined by the saturation of the carbon chains

• Saturated fatty acids pack tightly together and are solid at room temperature• Animal fats, butter, and lard are high in saturated

fatty acids

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© 2011 Pearson Education, Inc.

Triglycerides: Shape

• Unsaturated fatty acids do not stack together well and are more liquid at room temperature

• Hydrogen atoms at the unsaturated part can be arranged in different positions:• Cis: same side of the carbon chain• Trans: opposite sides of the chain

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© 2011 Pearson Education, Inc.

Triglycerides

• Hydrogenation: hydrogen atoms are added to unsaturated fatty acids• Make oils more solid and more saturated• Create trans fatty acids• Reduce oxidation; resist rancidity• Increase risk of cardiovascular disease

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Triglycerides

• Essential fatty acids: cannot be made by the body and must be obtained from food

• Linoleic acid (omega-6 fatty acid)• Found in vegetable and nut oils

• Alpha-linolenic acid (omega-3 fatty acid)• Found in vegetables, soy, flaxseeds, walnuts

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© 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc.

Triglycerides

• Omega-3 fatty acids found in fish and fish oil• Eicosapentaenoic acid (EPA)• Docosahexaenoic acid (DHA)

• Reduce risk of heart disease• Stimulate prostaglandins and thromboxanes that

reduce inflammatory responses • Reduce blood clotting and plasma triglycerides

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Phospholipids

• Phospholipids contain• Glycerol backbone, two fatty acids, phosphate

• Soluble in water• Transport fat in the bloodstream• Manufactured in our bodies (not required)

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© 2011 Pearson Education, Inc.

Sterols

• Sterols contain multiple rings of carbon atoms• Plant sterols appear to block the absorption of

dietary cholesterol• Cholesterol is made in our bodies and

therefore is not necessary in the diet• Sex hormones, vitamin D, bile

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© 2011 Pearson Education, Inc.

Digestion of Fats

• Fat digestion begins in the small intestine• Cholecystokinin (CCK) and secretin: gallbladder

contractions release bile• Bile is produced by the liver and stored in the

gallbladder• Bile emulsifies fat into small droplets• Pancreatic enzymes break fat into two fatty acids

and a monoglyceride

Fat Digestion

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© 2011 Pearson Education, Inc.

Absorption of Fats

• Lipoprotein transports lipids for absorption• Chylomicron: lipoprotein produced in intestine

to transport lipids from a meal• Composed of fatty acids surrounded by

phospholipids and proteins• Soluble in water

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Absorption of Fats

• Chylomicrons are absorbed by cells of the small intestine, then:• Travel through the lymphatic system• Transferred to the bloodstream

• Short- and medium-chain fatty acids are absorbed more quickly since they are not arranged into chylomicrons

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Absorption of Fats

• Triglycerides in the chylomicrons must be disassembled by lipoprotein lipase before they can enter body cells

• In body cells, triglycerides can be:• Used immediately for energy• Used to make lipid-containing compounds• Stored in muscle and adipose tissues

Lipid Absorption

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© 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc.

The Roles of Fat

• 9 kcal per gram• Major fuel at rest • Endurance exercise• Stored energy • Essential fatty acids• Fat-soluble vitamins

• Regulates cell function• Maintains membrane • Protects the body• Provides flavors and

textures of foods• Helps us feel satiated

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© 2011 Pearson Education, Inc.

How Much Fat?

• Acceptable Macronutrient Distribution Range (AMDR) for fat: 20−35% of calories

• Minimize saturated and trans fatty acid intake to lower risk of heart disease

• Active people may need more energy from carbohydrates and can reduce their fat intake to 20−25% of total calories

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How Much Fat?

• Dietary Reference Intakes (DRIs) set for essential fatty acids• Linoleic acid: AMDR of 5−10% of energy • Alpha-linolenic acid: 0.6−1.2% of energy• 5:1 to 10:1 ratio of linolenic:alpha-linolenic acid

• Saturated fat: less than 7% of energy• Trans fats: reduced to the absolute minimum

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Food Sources of Fat

• Visible fats• Fats we add to foods• Butter, cream, mayonnaise, salad dressings

• Invisible fats• Fats hidden within foods• Occur naturally or added during processing• Baked goods, dairy, meats, fast foods

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Food Sources of Fat

• Beneficial fats• Omega-3 fatty acids may be low in diets• Fish, walnuts, soy, canola, flaxseed

• Switching to more healthful fats without increasing total fat intake• Use olive or canola oil in place of butter or

margarine• Select low-fat or nonfat dairy products

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© 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc.

Food Sources of Fat

• Fat replacers• Used to lower fat content of foods• Found in chips, cakes, cookies• May cause GI side effects in large amounts• Example: olestra (Olean)

Fats in Food

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© 2011 Pearson Education, Inc.

Cardiovascular Disease

• Cardiovascular disease• Dysfunction of the heart or blood vessels• Can result in heart attack or stroke

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Cardiovascular Disease

• Risk factors for cardiovascular disease:• Being overweight• Physical inactivity• Smoking• High blood pressure• Diabetes mellitus• Inflammation

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Cardiovascular Disease

• Dietary fats increase blood lipids• Highly saturated and trans fat intakes

increase blood cholesterol • Omega-3 fatty acids reduce inflammation and

blood triglycerides

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Cardiovascular Disease

• Blood lipids include:• Chylomicrons—present only after a meal• Very-low-density lipoproteins (VLDL)• Low-density lipoproteins (LDL)• High-density lipoproteins (HDL)

Lipoproteins: VLDL, LDL, and HDL

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© 2011 Pearson Education, Inc.

Cardiovascular Disease

• Diets high in saturated fats• Decrease the removal of LDLs from the blood• Increase blood cholesterol levels• Contribute to the formation of plaques that can

block arteries

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© 2011 Pearson Education, Inc.

© 2011 Pearson Education, Inc.

Cardiovascular Disease

• Diets high in trans fatty acids:• Can raise blood levels of LDL-cholesterol as much

as saturated fat• Are abundant in hydrogenated vegetable oils

(margarine, baked goods, fried foods)

• FDA requires that trans fatty acid content be listed on labels for conventional foods and some dietary supplements

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Cardiovascular Disease

• Lifestyle changes can prevent or reduce cardiovascular heart disease• Total fat intake: 20−35% total calories• Saturated fat: less than 7% total calories• Cholesterol: less than 300 mg per day• Trans fat: reduce to absolute minimum• Increase omega-3 fatty acids• Dietary fiber: 20−30 grams per day• Folate: 400 micrograms/day

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Cardiovascular Disease

• Lifestyle changes can prevent or reduce cardiovascular heart disease• Maintain normal blood glucose level• Eat throughout the day• No more than 2 alcoholic beverages per day for men and

1 drink per day for women• Maintain an active lifestyle• Maintain a healthful body weight• Decrease salt intake (DASH diet)

Fast Food Trends

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Cardiovascular Disease

• Medicines help reduce risk• Endogenous cholesterol synthesis inhibitors:

statins• Bile acid sequestrants• Nicotinic acid