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Lipids

Types of Lipids (fat)

• Triglycerides– Fatty acids

• Phospholipids• Sterols

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Triglycerides

Most common lipid in food and body

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Fatty Acids Are Carbon Chains of Varied Length

• Long chain fatty acids– 12 or more carbons

• Medium chain fatty acids– 6-10 carbons

• Short chain fatty acids– Less than 6 carbons

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Fatty Acids Vary in Saturation

• Saturated fatty acids (SFA)– No double bonds

• Monounsaturated fatty acids (MUFA)– One double bond

• Polyunsaturated fatty acids (PUFA)– Many double bonds

Saturation

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The Carbon Chain Shape Varies with Saturation

• Unsaturated cis fatty acids– Bent (kinked) carbon chain

• Trans and saturated fatty acids – Straight carbon chain

• Hydrogenation– Adding hydrogen to make an unsaturated fat

more saturated: results in trans fatty acids

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Food Sources of Triglycerides• Animal fats and vegetable oils

– described by the predominate fatty acid• Dairy

– Low-fat products are available• Grains

– Naturally low in fat, except when fat is added (e.g. pastries, pancakes)

• Fruits and Vegetables– Low in fat except avocados and coconuts

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Functions of Triglycerides

• Provide Energy• Provide Compact Energy Storage• Insulate and Protect the Body• Aid Fat-Soluble Vitamin Absorption and

Transport• Essential Fatty Acid Functions

– Eicosanoids

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Phospholipids

• Hydrophobic and Hydrophillic Ends• Functions

– Components of cell membranes– Emulsifiers (e.g., bile)

• Sources– Synthesized by the body– Food: egg yolks, wheat germ and peanuts

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Sterols• Carbons arranged in rings• Most well-known sterol is cholesterol• Functions

– Steroid hormones, bile, cell membranes, lipoprotein shell (e.g., chylomicrons)

• Sources– Synthesized by the body– Foods of animal origin (cholesterol) and plants

(plant sterols such as sitostanol)

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Recommended Fat Intakes

• No RDA• AMDR: 20-35%• Dietary Guidelines 2010:

– Limit saturated and trans fat• AHA recommendations for those at risk for

heart disease:– Limit saturated fats to 7% of total calories– Limit cholesterol intake to less than 200 mg

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Fat Intake

• North American fat intake has doubled in the last century

• Omega 6 intakes are plentiful• Omega 3 intakes are usually low

– Food sources: cold-water fish, walnuts, flaxseeds, soybeans.

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Fat Digestion

• Mouth– Lingual lipase

• Stomach– Gastric lipase

• Small Intestine– CCK triggers bile– Bile emulsifies fat micelles are formed

acted upon by pancreatic lipase and colipase

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Fat Digestion in the Small Intestine

• Triglycerides are broken down into monoglycerides and free fatty acids

• Phospholipids are broken down into free fatty acids, glycerol and phosphoric acid

• Cholesterol esters are broken down into cholesterol and free fatty acids

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Fat Absorption

• 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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Cardiovascular Disease (CVD)• Major killer of North Americans• Development of CVD

– Atherosclerotic plaque– Heart attack and stroke

• Risk factors for CVD– age, gender, race and genetics (cannot change)– blood cholesterol and triglyceride levels,

hypertension, smoking, physical inactivity, obesity, diabetes and other diseases (can change or prevent)

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Preventing CVD• 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

• Include 2 grams plant stanols/sterols daily

• Soluble fiber intake of 20-30g

• Moderate sugar intake

• Keep body weight at a healthy level

• Increase physical activity