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Lipids: Not Just Fat Chapter 6 Lipids • Essential nutrients • Provide energy • Help transport fatsoluble nutrients • Contribute to flavor and texture of food Photo © PhotoDisc Lipids • What are lipids? – Triglycerides • Stored in adipose tissue • Fats and oils in food – Phospholipids • Plant and animal origin • Body can make them • Soluble – Sterols • Cholesterol Fatty Acids Are Key Building Blocks • Fatty acid – Determines solid or liquid • Chain length – 4 to 24 carbon length Fatty Acids Are Key Building Blocks • Saturation – Saturated fatty acid • All single bonds between carbons – Monounsaturated fatty acid • One carbon–carbon double bond – Polyunsaturated fatty acid • More than one carbon–carbon double bond Fatty Acids Are Key Building Blocks • Cis vs. trans – Cis fatty acids • Occur naturally • Chain is bent – Trans fatty acids • Produced by hydrogenation • Chain is straighter Fatty Acids Are Key Building Blocks • Nonessential and essential fatty acids – Nonessential fatty acids • Can be made in the body • Not “essential” to have in your diet Fatty Acids Are Key Building Blocks • Nonessential and essential fatty acids – Essential fatty acids • Can’t be made in the body • Must come from food • Linoleic acid and alpha-linolenic acid • Used to make eicosanoids Triglycerides • Structure – Glycerol + three fatty acids • Functions – Energy source • 9 kcal/g – Energy reserve • Form of stored energy in adipose tissue – Insulation and protection • Visceral fat – Carrier of fat-soluble vitamins – Sensory qualities in food Triglycerides • Functions – Insulation and protection • Visceral fat – Carrier of fat-soluble vitamins – Sensory qualities in food Triglycerides in Food • Sources of omega-3 fatty acids – Soybean, canola, walnut, flaxseed oils – Salmon, tuna, mackerel, fish-oil supplements • Sources of omega-6 fatty acids – Seeds, nuts, vegetable oils – Meat, poultry, eggs • Commercial processing – Oxidation Photos © PhotoDisc Phospholipids • Structure – Glycerol + two fatty acids + phosphate group • Phospholipid functions – Keeps fat suspended in water – Component of cell membranes – Lipid transport as part of lipoproteins – Emulsifiers • Food sources – Egg yolks, liver, soybeans, peanuts Sterols: Cholesterol • Functions – Component of cell membranes – Precursor to other substances • Vitamin D • Sterol hormones • Bile salts • Synthesis – Made in the liver • Sterols in food – Found only in animal foods Lipid Digestion and Absorption • Digestion of triglycerides and phospholipids – Mouth and stomach • Minimal digestion of triglycerides – Small intestine • Emulsified by phospholipids • Digested by pancreatic lipase • Absorbed into intestinal cells –Formed into chylomicrons and moved into lymphatic system Lipids in the Body • Lipid absorption – Micelles – Lipoproteins carry lipids around the body – Chylomicrons • Deliver dietary lipids from intestines to cells and liver Lipids in the Body • Digestion and absorption of sterols – About 50% of dietary cholesterol is absorbed • Dietary fat increases absorption • Dietary fiber decreases absorption Lipids in the Body • Very-low-density lipoproteins (VLDL) – Deliver triglycerides to cells • Low-density lipoproteins (LDL) – Deliver cholesterol to cells • High-density lipoproteins (HDL) – Pick up cholesterol for removal or recycling Lipids in the Diet • Recommended intake – Reduce saturated and trans fat intake – Total fat: 20–35% of calories – Need approximately 2% of kilocalories as essential fatty acids – Improve balance of omega-3 and omega-6 fatty acids Photos © PhotoDisc Lipids in the Diet • Fat replacers – Different types of composition – Olestra • Sucrose + fatty acids • Indigestible— provides no calories • Reduces absorption of fatsoluble vitamins Lipids and Health • Obesity – High-fat diets promote weight gain • Heart disease – Major risk factors • High blood cholesterol –High LDL and low HDL • Smoking • High blood pressure Lipids and Health • Atherosclerosis – Slow hardening and narrowing of arteries – Promoted by high blood cholesterol – Lipoprotein a [Lp(a)] – C-reactive protein Lipids and Health • Reducing heart disease risk – AHA diet and lifestyle recommendations • Consume an overall healthy diet • Aim for a healthy body weight • Aim for a desirable lipid profile • Aim for normal blood pressure • Aim for normal blood glucose levels • Avoid use of and exposure to tobacco products Lipids and Health • Reduce heart disease risk – AHA recommendations plus other risk factors • Balance calorie intake and physical activity to achieve or maintain a healthy body weight • Consume a diet rich in fruits and vegetables • Choose whole-grain, high-fiber foods • Consume fish at least twice a week • Limit your intake of saturated and trans fat and cholesterol Lipids and Health • Reduce heart disease risk – AHA diet and lifestyle recommendations • Minimize your intake of beverages and foods with added sugars • Choose and prepare foods with little of no salt • If you consume alcohol, do so in moderation • Follow the AHA recommendations when eating outside of the home Lipids and Health • Metabolic syndrome – Cluster of at least three symptoms • Excess abdominal fat • High blood glucose • High serum triglycerides • Low HDL cholesterol • High blood pressure Lipids and Health • Putting it all together – Healthy People 2010 objectives target reducing deaths from heart disease and stroke and reducing the number of adults with high blood cholesterol levels Lipids and Health • Cancer – Stages of development • Initiation • Promotion • Progression – Role of diet • Factors that promote or protect Lipids and Health • Cancer – Nutrition and physical activity guidelines for cancer prevention • Maintain a healthful weight • Adopt a physically active lifestyle • Consume a healthy diet • If you drink alcohol, limit consumption