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chapter 5 notes - Chapter Summary for Nutrition Concepts...

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Chapter Summary for  Nutrition: Concepts and Controversies  11e Chapter 5 – The Lipids: Fats, Oils, Phospholipids, and Sterols Lipids not only serve as energy reserves but also cushion the vital organs, protect the body from temperature extremes, carry the fat-soluble nutrients and phytochemicals, serve as raw materials, and provide the major component of which cell membranes are made. Lipids provide more energy per gram than carbohydrate and protein, enhance the aromas and flavors of foods, and contribute to satiety, or a feeling of fullness, after a meal. The body combines three fatty acids with one glycerol to make a triglyceride, its storage form of fat. Fatty acids in food influence the composition of fats in the body. Fatty acids are energy-rich carbon chains that can be saturated (filled with hydrogens), monounsaturated (with one point of unsaturation), or polyunsaturated (with more than one point of unsaturation). The degree of saturation of the fatty acids in a fat determines the fat’s softness or hardness. Phospholipids, including lecithin, play key roles in cell membranes; sterols play roles as part of bile, vitamin D, the sex hormones, and other important compounds. In the stomach, fats separate from other food components. In the small intestine, bile emulsifies the fats, enzymes digest them, and the intestinal cells absorb them. Small lipids travel in the bloodstream unassisted. Large lipids are incorporated into chylomicrons for transport in the lymph and blood. Blood and other body fluids are watery, so fats need special transport vehicles—the lipoproteins—to carry them in these fluids. When low on fuel, the body draws on its stored fat for energy. Carbohydrate is necessary for the complete breakdown of fat. Energy from fat should provide 20 to 35 percent of the total energy in the diet; intakes of saturated fat, trans fat, and cholesterol should be kept low. The chief lipoproteins are chylomicrons, VLDL, LDL, and HDL. Blood LDL and HDL concentrations are among the major risk factors for heart disease. Elevated blood cholesterol is a risk factor for cardiovascular disease. Among major dietary factors that raise blood cholesterol, saturated fat and trans fat intakes are most influential. Dietary cholesterol raises blood cholesterol to a lesser degree. Trimming fat from food trims calories and, often, saturated fat and trans fat as well. Dietary measures to lower LDL in the blood involve reducing saturated fat and trans fat and substituting monounsaturated and polyunsaturated fats. Cholesterol-containing foods are nutritious and for most people are best used in moderation. Two polyunsaturated fatty acids, linoleic acid (an omega-6 fatty acid) and linolenic acid (an omega-3 acid), are essential nutrients used to make substances that perform many important functions. The omega-6 family includes linoleic acid and arachidonic acid. The omega-3 family includes linolenic acid, EPA, and DHA. The principal food source of EPA and DHA is fish, but some species have become contaminated with environmental pollutants.
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