Understanding Lipids: Fats and Oils

1. Chapter 5 The Lipids: Fats and Oils

2. Ask Yourself True or False? The body can store fat in virtually unlimited amounts. 2. Dietary cholesterol is found only in animal foods. 3. A person’s blood level of cholesterol is a predictor of that person’s risk of having a heart attack. 4. For the health of your heart, the fat you should avoid eating, most of all, is cholesterol. 5. The more monounsaturated fats you consume, the better it is for your health.

3. Ask Yourself 6. Fruits are essentially fat-free. 7. In general, the softest margarines are the most polyunsaturated. 8. Polyunsaturated fat has the same number of calories as saturated fat. 9. All the foods you eat should contain less than 10% of calories from saturated fat. 10. No one is free of atherosclerosis.

4. A Primer on Fats Lipids: a family of compounds that includes: Triglycerides (fats and oils) Phospholipids (lecithin) Sterols (cholesterol) Obvious sources of fat are oil, butter, margarine, and shortening. Other foods contributing fat include meat, nuts, mayonnaise, salad dressings, eggs, bacon, gravy, cheese, ice cream, and whole milk.

5. A Primer on Fats Fats Lipids that are solid at room temperature. Oils Lipids that are liquid at normal room temperature.

6. Muscles derive fuel from fat.

7. A Primer on Fats After eating, the body stores some fat as an energy reserve. The body has unlimited potential to store fat. Excess carbohydrate and protein can be converted to fat, but they cannot be made from fat. One pound of body fat is worth 3,500 calories. Within the fat cell, lipid is stored in a droplet. This droplet can enlarge, and the cell membrane will grow to accommodate its swollen contents.

8. Fat droplet Cell membrane Cell nucleus

9. Satiety The feeling of fullness or satisfaction that people feel after meals. Fats slow the rate at which the stomach empties. A Primer on Fats

10. A Closer View of Fats • Excess energy from the energy-yielding nutrients is stored as fat. • The fat is first broken into fragments called fatty acids. • Fatty acids Basic units of fat composed of chains of carbon atoms with an acid group at one and and hydrogen atoms attached all along their length.

11. Triglycerides The major class of dietary lipids, including fats and oils. A triglyceride is made up of three units known as fatty acids and one unit called glycerol. Glycerol An organic compound that serves as the backbone for triglycerides. A Closer View of Fats About 95 percent of the lipids in foods and in the human body are triglycerides.

12. Glycerol Fatty acid Fatty acid + Fatty acid Glycerol + Fatty acids Triglyceride

13. A Closer View of Fats: Other Lipids Phospholipid A lipid similar to a triglyceride but containing phosphorus; one of the three main classes of lipids. Examples include: Lecithin A major constituent of cell membranes, manufactured by the liver and found in many foods. Sterols Lipids with a structure similar to that of cholesterol; one of the three main classes of lipids. Examples include: Cholesterol One of the sterols, manufactured in the body for a variety of purposes.

14. A Closer View of Fats Fatty Acids differ in chain length or the number of carbons in a fatty acid. Chain length affects solubility. Fatty acids can be: Short-chain Medium-chain Long-chain

15. A Closer View of Fats Fatty acids differ in the degree of saturation. Saturation refers to the chemical structure—specifically to the number of hydrogens the fatty acid chain holds. Saturated fatty acids are filled to capacity with hydrogen. Unsaturated fatty acids hold an “empty spot” or point of unsaturation.

16. Saturated vs. Unsaturated Fats Saturated fatty acid A fatty acid carrying the maximum possible number of hydrogen atoms (having no points of unsaturation). Saturated fats are found in animal foods like meat, poultry, and full-fat dairy products, and in tropical oils such as palm and coconut.

17. Unsaturated fatty acid: a fatty acid with one or more points of unsaturation. Unsaturated fats are found in foods from both plant and animal sources. Unsaturated fatty acids are further divided into monounsaturated fatty acids and polyunsaturated fatty acids. Monounsaturated fatty acid:a fatty acid containing one point of unsaturation, found mostly in vegetable oils such as olive, canola, and peanut. Saturated vs. Unsaturated Fats

18. Saturated vs. Unsaturated Fats Polyunsaturated fatty acid:(sometimes abbreviated PUFA) a fatty acid in which two or more points of unsaturation occur, found in nuts and vegetable oils such as safflower, sunflower, and soybean, and in fatty fish.

19. Saturated vs. Unsaturated Fats

20. The Essential Fatty Acids The human body can synthesize all fatty acids except: Linoleic acid, linolenic acid Polyunsaturated fatty acids, essential for human beings. Essential fatty acid A fatty acid that cannot be synthesized in the body in amounts sufficient to meet physiological need.

21. Omega-6 vs. Omega-3 Fatty Acids Omega-3 fatty acids, found in fish oils, offer a protective effect on health. Interest in fish oils first kindled when someone thought to ask why the Eskimos of Greenland, who eat a diet very high in fat, have such a low rate of heart disease. Blood clot formation, inflammation (e.g. arthritis, asthma), irregular heart rhythm, and cancer also seem to be beneficially affected by DHA and/ or EPA.

22. Something’s Fishy Eating fish at least two times per week as part of a balanced diet can: • Reduce blood clot formation ( heart attacks and strokes). • Decrease risk of heart arrhythmias. • Decrease blood triglycerides. • Decrease atherosclerotic plaque formation. • Improve health of arteries. • Slightly lower blood pressure.

23. Characteristics of Fats in Foods The more unsaturated a fat, the more liquid it is at room temperature. The more polyunsaturated the fat is, the sooner it melts.

25. Characteristics of Fats in Foods Unsaturated fats are more likely to react with oxygen and become rancid. Food manufacturers may alter fats and oils by: Hydrogenation The process of adding hydrogen to unsaturated fat to make it more solid and more resistant to chemical change. Antioxidants A compound that protects other compounds from oxygen by itself reacting with oxygen. Emulsifiers A substance that mixes with both fat and water and can break fat globules into small droplets, thereby suspending fat in water.

26. Other Members of the Lipid Family Phospholipids… Important components of cell membranes. Can serve as emulsifiers in the body, joining with both water and fat. Also used in foods such as margarine, chocolate, salad dressings, and frozen desserts to keep the fats dispersed. Widespread in foods. A Phospholipid: Lecithin

27. Sterols such as cholesterol Incorporated as an integral part of the structure of cell membranes. Used to make bile for digestion. Used to make sex hormones (estrogen and testosterone). Made into vitamin D. Deposited in the artery walls, leading to plaque buildup and heart disease. Other Members of the Lipid Family Sterols such as cholesterol have a multiple-ring structure.

29. Digestion of fat

30. A. Digestion of Fat 1. Mouth Some hard fats begin to melt as they reach body temperature. Mouth Salivary glands 2. Stomach The stomach’s churning action mixes fat with water and acid. A stomach enzyme accesses and breaks apart a small amount of fat. Fat is last to leave the stomach. Liver 3. Liver, Gallbladder, and Small Intestine Once in the small intestine, fat encounters bile, an emulsifier made in the liver (see Part B). The gallbladder, a storage organ, squirts bile into the contents of the small intestine to blend the fat with the watery digestive secretions. Stomach Pancreas Small intestine Gallbladder 4. Pancreas Fat-digesting enzymes from the pancreas (pancreatic lipase) enter the small intestine. The enzymes can attack fat only after emulsification by bile. They break down the triglycerides to fatty acids, glycerol, and monoglycerides. Large intestine 5. Large intestine Some fat and cholesterol, trapped in fiber, are carried out of the body with other wastes.

31. How the Body Handles Fat The products of fat digestion are fatty acids, glycerol, and monoglycerides. Monoglyceride A glycerol molecule with one fatty acid attached to it. A diglyceride is a glycerol molecule with two fatty acids attached to it. The shortest fatty acids and glycerol pass by simple diffusion into the absorptive cells and without further processing can enter the blood stream, travel to the liver, and be converted and used by the body.

33. How the Body Handles Fat Bile A mixture of compounds, including cholesterol, made by the liver, stored in the gallbladder, and secreted into the small intestine. Bile emulsifies lipids to ready them for enzymatic digestion and helps transport them into the intestinal wall cells.

34. Long-chain fatty acids, phospholipids, and cholesterol are insoluble in water and cannot be accepted by the body’s blood and lymph system. Lymph The body fluid that transports the products of fat digestion toward the heart and eventually drains back into the bloodstream. Lymph consists of the same components as blood with the exception of red blood cells. These fats must be packaged into one of four types of lipoproteins for transport. How the Body Handles Fat

35. Lipoproteins Clusters of lipids associated with protein that serve as transport vehicles for lipids in blood and lymph. The four main types of lipoproteins are: Chylomicron A type of lipoprotein that transports newly digested fat—mostly triglyceride—from the intestine through lymph and blood. VLDL (very-low-density lipoprotein) Carries fats packaged or made by the liver to various tissues in the body. LDL (low-density lipoprotein) Carries cholesterol (much of it synthesized in the liver) to body cells. A high blood cholesterol level usually reflects high LDL. HDL (high-density lipoprotein) Carries cholesterol in the blood back to the liver for recycling or disposal. How the Body Handles Fat

37. C. Absorption of Fat: The Chylomicron Most of the newly digested fats are absorbed into lymph as part of a special package—the chylomicron. A chylomicron (lipoprotein) contains an interior of triglycerides and cholesterol surrounded by phospholipids. Proteins cover the structure. Such an arrangement of hydrophobic (water- fearing) molecules (the fatty acids) on the inside and hydrophilic (water- loving) molecules (proteins) on the outside allows lipids to travel through the watery fluids of the body. Phospholipid Cholesterol Triglyceride Protein

39. A. Functions and Interactions of Lipoproteins Newly digested fats are transported by chylomicrons. Small intestine Chylomicron Lipids processed or made in The liver are released in VLDL. VLDL Fat is made available to body cells via enzyme action; afterward, the remnants of the chylomicron are returned to the liver. VLDL makes fats available to body cells via enzyme action. Remnants of chylomicron return to liver. Liver LDL (derived from VLDL) carriesfats (mostly cholesterol) to body cells. LDL travels through blood vessels, is vulnerable to attack by oxygen, and has affinity for linings of artery walls—contributing to plaque buildup. (Cholesterol) HDL HDL transports cholesterol from body cells back to liver for recycling or disposal. LDL Body cells

41. “Good” vs. “Bad” Cholesterol ATHEROSCLEROSIS: As LDL particles penetrate the walls of the arteries, they become oxidized-LDL and next are scavenged by the body’s white blood cells. These foam cells are then deposited into the lining of the artery wall. This process, known as atherosclerosis, causes plaque deposits to enlarge, artery walls to lose elasticity, and the passage through the artery to narrow.

42. Oxidized LDL-cholesterol The cholesterol in LDLs that is attacked by reactive oxygen molecules inside the walls of the arteries. Oxidized LDL is taken up by scavenger cells and deposited in plaque. Foam cells: Cells from the immune system containing scavenged oxidized LDL-cholesterol that are thought to initiate arterial plaque formation. “Good” vs. “Bad” Cholesterol

43. Atherosclerosis

44. Smooth muscle layer Artery lining Vessel opening Plaque Normal artery Early injury triggers inflammation* Oxidized LDL Atherosclerosis Scavenger + oxidized LDL (incorporated into lining of artery as Cholesterol loaded foam cell) White blood cell (scavenger) LDL + oxygen White blood cell Muscle cells Accumulation of cholesterolloaded foam cells—plaque formation

50. Phytochemicals Physiologically active compounds found in plants that appear to help promote health and reduce risk for cancer, heart disease, and other conditions. Fats Can Be Healthy