Chapter Summary for
Nutrition: Concepts and Controversies
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,
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
are most influential. Dietary cholesterol raises blood cholesterol to a lesser degree. Trimming fat from food trims
calories and, often, saturated fat and
fat as well. Dietary measures to lower LDL in the blood involve reducing
saturated fat and
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.
Vegetable oils become more saturated when they are hydrogenated. Hydrogenated fats resist rancidity better, are