Chapter 5 Nutrition
Describe a fatty acid.
A fatty acid is a chain of carbon atoms flanked by hydrogen atoms. Each carbon atom can form a maximum of four chemical bonds. In fatty acids, the carbon atoms are bonded to other carbon atoms, hydrogen atoms, or oxygen atoms. Fatty acids can vary in length, degree of saturation (i.e., the presence of one or more double bonds), and shape.
Name the four major lipoproteins, describe their composition, and explain their functions in the body.
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Note that the newest Dietary Guidelines and latest AHA recommendations no longer set limits on dietary cholesterol.
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Recall that fats are not soluble in water; lipoproteins are the solution for transporting lipids in the watery environment of the blood.
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Recall that lipids do not dissolve in water.
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Recognize that a low-fat diet is not necessarily a healthy diet; fat quality is as important as fat quantity when it comes to promoting health.
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Recognize that cholesterol is only found in foods of animal origin.
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Recognize that chylomicrons arise from the GI tract, while VLDLs, LDLs, and HDLs arise from the liver.
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Study Table 5-2, which summarizes the health effects and food sources of various types of fatty acids.
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Summarize the diet and lifestyle recommendations of the American Heart Association.
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Summarize the process of fat absorption.
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Summarize the process of fat digestion.
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Identify food sources of fat (i.e., triglycerides).
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List strategies used by food manufacturers to limit rancidity in food products.
Addition of preservatives (e.g., antioxidants) that delay oxidation of fatty acids Packaging that limits exposure to light, heat, and oxygen Hydrogenation
Identify the two essential fatty acids in the human diet.
Alpha-linolenic acid (an omega-3 fatty acid) Linoleic acid (an omega-6 fatty acid)
List food sources of the essential fatty acids.
Alpha-linolenic acid (some people do not get enough omega-3 fatty acids) Walnuts Canola oil Chia seeds Flax seeds Perilla oil Hempseed oil Linoleic acid (most people get more omega-6 fatty acids than they need) Beef Poultry Safflower oil Sunflower oil Corn oil
Recall good food sources of saturated, monounsaturated, and polyunsaturated fatty acids.
As mentioned above, a triglyceride contains three fatty acids, each of which may be saturated or unsaturated. Although the fats in foods are a mixture of different fatty acids, foods sources of fat are generally categorized based on the most abundant type of fatty acid they contain.
Define atherosclerosis.
Atherosclerosis refers to the buildup of fatty material (plaque) inside the blood vessels. Atherosclerotic plaque is made of lipids (especially oxidized LDLs), white blood cells, smooth muscles cells, proteins, and calcium. Accumulation of plaque can narrow blood vessels, restricting blood flow to tissues (e.g., heart or brain)
Recognize that partially hydrogenated oils are a source of trans fatty acids.
During the chemical process of changing unsaturated fatty acids into more saturated fatty acids, some trans fatty acids are formed.
Recall guidelines for consumption of seafood to obtain omega-3 fatty acids.
Eat 2 or more servings of fatty fish each week. Broiled or baked is better than fried. Fish oil capsules (~1 g/d of omega-3 fatty acids) can provide health benefits for people who do not eat fish.
List food sources of phospholipids
Eggs Peanuts Wheat germ Organ meats Lecithin is often added to foods (e.g., salad dressing) as an emulsifier
List and describe the roles of lipids in the body.
Energy storage Insulation/cushion Transport of fat-soluble vitamins Synthesis of hormones and other compounds that regulate body processes Component of cell membranes
Recall why HDLs and LDLs are called "good" and "bad" cholesterol.
High-density lipoproteins remove cholesterol from the blood vessels and return it to the liver, where it can be recycled into other lipoproteins or made into bile. Because it removes lipids from the blood, HDL is called the "good" cholesterol. Low-density lipoproteins deliver cholesterol to the tissues. LDLs contribute to the formation of plaque in the blood vessels, so LDL is called the "bad" cholesterol.
Recall the definition of essential fatty acid.
In nutrition, a nutrient is essential if it cannot be made in the body; it must be consumed in the diet The two essential fatty acids are precursors for the synthesis of other fatty acids and important chemicals in the body that form cell membranes and function as regulators of neurological development, vision, immune function, blood clotting, and inflammation.
Summarize the development of atherosclerosis; recognize the significance of LDL and HDL in this process.
LDL promotes formation of atherosclerotic plaque. HDL removes cholesterol from the blood stream.
List food sources of cholesterol.
Organ meats Egg yolks Shellfish
Describe the structure of a phospholipid.
Phospholipids are composed of two fatty acids and one phosphate-containing group bound to a glycerol backbone.
State the functions of phospholipids.
Phospholipids have the unique quality of being simultaneously soluble in fat and water Component of all cell membranes Emulsifiers (help to suspend fats in a watery environment) Component of lipoproteins, which transport fat in the blood
Explain why "fat-free" is not necessarily the same as "healthy."
Reducing fat content may alter the flavor and texture of foods, so food manufacturers may add sugar and salt to compensate.
Differentiate between cis and trans unsaturated fatty acids.
The terms cis and trans refer to the specific shape of an unsaturated fatty acid. When a fatty acid is unsaturated, the carbon chain is bent. In cis unsaturated fatty acids, the ends of the carbon chain lie on the same side of the double bond. In nature, most unsaturated fatty acids exist in the cis form. In trans fatty acids, the ends of the carbon chain lie on different sides of the double bond. Trans fatty acids are formed during food processing (e.g., hydrogenation of oils or deep frying). Trans fats are not good for heart health because they worsen blood cholesterol levels.
Differentiate between omega-3 and omega-6 polyunsaturated fatty acids.
The terms omega-3 and omega-6 simply refer to the location of the double bonds in an unsaturated fatty acid. The specific structure of a fatty acid determines its functions in the body. Omega-3 fatty acids In the body, omega-3 fatty acids tend to decrease blood clotting, decrease inflammation, and decrease triglycerides in the blood (generally good for heart health and brain health) Examples: alpha-linolenic acid (essential), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) Rich food sources: fish, walnuts, canola oil, chia seeds Omega-6 fatty acids In the body, omega-6 fatty acids tend to increase blood clotting and promote the inflammatory response; they also are involved in regulation of blood pressure. Examples: linoleic acid (essential), arachidonic acid Rich food sources: safflower oil, sunflower oil, corn oil, beef, poultry Humans need a balance of omega-3 and omega-6 fatty acids
Recall the importance of the lymphatic system for absorption of lipids.
Water-soluble nutrients and small fats (short- and medium-chain fatty acids) can be absorbed directly from the small intestine into the bloodstream. These nutrients are carried via the hepatic portal vein to the liver. Most of the lipids and fat-soluble vitamins in the diet are too large to enter the capillaries, however. Dietary lipids are packaged as chylomicrons and absorbed via the lacteals (lymph vessels). These nutrients are transported via the lymphatic system, which empties into the bloodstream. Once in the bloodstream, chylomicrons circulate through the body, delivering fatty acids and cholesterol to body tissues.
Differentiate between saturated and unsaturated fatty acids.
saturated: contains no carbon-carbon double bonds; the fatty acid chain is fully saturated with hydrogen atoms; typically solid at room temperature Unsaturated: contains at least one carbon-carbon double bond (i.e., the fatty acid chain is not fully saturated with hydrogen atoms); typically liquid at room temperature Monounsaturated: contains one carbon-carbon double bond Polyunsaturated: contains more than one carbon-carbon double bond
List common food sources of trans fatty acids.
Stick margarine Vegetable shortening Commercially prepared baked goods Deep fried foods
Identify one example of a phospholipid.
Lecithin (a.k.a. phosphatidylcholine) is the most common phospholipid found in the diet and in the body.
Define cardiovascular disease, myocardial infarction, and cerebrovascular accident.
Cardiovascular disease: disease of the heart and/or blood vessels; usually characterized by accumulation of plaque in the blood vessels Myocardial infarction (a.k.a. heart attack): death of part of the heart muscle, typically caused by restriction/blockage of blood flow to the heart muscle Cerebrovascular accident (a.k.a. stroke): death of part of the brain tissue, typically caused by a blood clot
Describe the process of hydrogenation.
Chemically changing unsaturated fatty acids into saturated fatty acids by adding hydrogen to double bonds Changes a liquid oil into a more solid fat EXAMPLE: Food processing changes liquid vegetable oils into margarine
Identify examples of sterols.
Cholesterol (produced by animals) Phytosterols (produced by plants)
Understand that cholesterol in foods is not yet in the form of HDLs and LDLs; it is not until lipids are processed by the liver that they are in the form of HDLs and LDLs.
Cholesterol is just one component of lipoproteins.
State the functions of sterols.
Component of cell membranes Component of nervous tissue Synthesis of hormones (e.g., testosterone) Precursor to bile acids (participate in fat digestion)
Recall recommendations from the Dietary Guidelines and American Heart Association for intake of saturated fat and trans fat.
DGAs recommend limiting saturated fat intake to 10% of total kcal. To reduce risk of cardiovascular disease, AHA recommends limiting saturated fat intake to 5% to 6% of total kcal. Both authorities recommend avoiding trans fat.
Define rancidity.
Exposure to light, heat, and oxygen causes fatty acids to decompose, resulting in unpleasant tastes and odors Polyunsaturated fatty acids are most susceptible to rancidity. Rancidity limits the shelf-life of foods that contain unsaturated fats.
Review the definitions of these common nutrient claims on food labels.
Fat-free: <0.5 g of fat per serving Low-fat: ≤3 g of fat per serving Reduced-fat: at least 25% less fat than reference food
State the AMDR for fat.
For adults, fat should make up 20% to 35% of total kcal.
List risk factors for cardiovascular disease.
High blood cholesterol Smoking Hypertension Diabetes Low HDL Advanced age Family history Obesity
Know the difference between lipoproteins and phospholipids.
Lipoproteins are the mode of transport for lipids in the blood. All the lipoproteins are made of a core of lipids (mixture of triglycerides and cholesterol) surrounded by a shell of proteins and phospholipids. Phospholipids are just one component of lipoproteins. Remember that phospholipids are simultaneously soluble in fat and water. They form a shell around triglycerides and cholesterol so that these important nutrients can be transported through the watery environment of the blood to the body tissues, where they are needed.
Describe the roles of fat in foods.
Many flavors dissolve in fat Smooth, creamy texture
Describe the structure of a sterol.
Sterols are multiring structures. Some sterols have a fatty acid tail.
Describe the Mediterranean diet and discuss its health effects (review from Chapter 2).
Traditional dietary pattern of the southern Mediterranean region Plant-based (but not vegetarian) diet Olive oil is the main source of dietary fat Moderate intake of red wine Associated with long life expectancy and low rates of chronic disease
List the three forms of lipids.
Triglycerides Phospholipids Sterols
Describe the structure of a triglyceride.
Triglycerides are composed of three fatty acids attached to a glycerol backbone. The individual fatty acids in the triglyceride may be saturated or unsaturated and may vary in length.
State the function of triglycerides
Triglycerides are the main form of lipids in foods and in the body. The purpose of a triglyceride is to store energy.
