Lipids: Not Just Fat

1. Lipids: Not Just Fat BIOL 103, Chapter 6

2. Today’s Topics • What are Lipids? • Fatty Acids are Key Building Blocks • Triglycerides • Phospholipids • Sterols • Lipids Digestion and Absorption • Lipids in the Body • Lipids in the Diet • Lipids and Health

3. Lipids • Essential nutrients • Provide energy • Help transport fat-soluble nutrients • Contribute to flavor and texture of food

4. What are Lipids? • Lipids include… • Triglycerides (most abundant lipids) • In body: stored in adipose tissue • In food: “fats and oils” • Phospholipids (~2% of dietary lipids) • Plant and animal origin • Body can make them • Soluble in fat and water • Sterols (very, very small % of lipids) • Most well known: Cholesterol

5. Fatty Acids are Key Building Blocks • Fatty Acids • Determine whether a fat is solid or liquid at room temperature • Basic structure: (-COOH); (-CH3) • Chain length • 2-24 Carbon length

6. Fatty Acids are Key Building Blocks • Saturation • Saturated fatty acids • All single bonds between carbons • Unsaturated fatty acids • One or more carbon bonds is a double bond • Monounsaturated fatty acid (MUFA) • Polyunsaturated fatty acid (PUFA) • Fats with more double bonds are generally more liquidy

7. Saturated vs. Unsaturated Fatty Acids

8. Fatty Acids are Key Building Blocks Cis fatty acids Trans fatty acids Produced by hydrogenation (adds hydrogen to an unsaturated fatty acids) A small portion of trans fat can occur naturally Chain is straighter • Occurs naturally • Chain is bent

9. Trans Fat • In health, trans fatty acids are known to raise LDL (“bad”) cholesterol, and lower HDL (“good cholesterol”), promote systemic inflammation, and increase triglycerides in your blood. • History and how it is made: • In Europe (1910) • In US (1960s)

10. 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

11. Fatty Acids are Key Building Blocks • Nonessential and essential fatty acids (cont.) • Essential fatty acids • Can’t be made in the body • Must come from food • Omega-3 (alpha-linolenic acid) and omega 6 (linoleic acid) • Used to make eicosanoids

12. Triglycerides • Structure • Glycerol + 3 Fatty Acids • Functions • Energy source: 9 kcal/g • Energy reserve: form of stored energy in adipose tissue (“fatty tissue”) • Insulation and protection: • Visceral fat (fat around organs) • Subcutaneous fat (fat under skin to protect/insulate body) • Carrier of fat-soluble nutrients • Sensory qualities in food

13. Apple vs. Pear

14. Triglycerides in Food • Found in a variety of fats and oils • Classified by their most prevalent type • Saturated fatty acids: animal foods and tropical oils • Polyunsaturated fatty acids: plant or animal based • Omega-3: soybean, flaxseed oils; salmon, tuna • Omega-6: seeds, nuts, corn oil, meat, poultry, eggs

15. What are the positive and negative consequences of hydrogenating a fat?(Problem Set 6, #3) Pros Cons • Oxidation causes food to spoil and damage body tissues

16. Phospholipids • Structure • Glycerol + 2 fatty acids + phosphate group • Functions: • Emulsifiers • Keep fat suspended in water • Keep oil and water mixed • Structural element for cell membranes

17. Phospholipids • Cell membrane • Double layer of phospholipids • Store fatty acids temporarily and release them as needed  can regulate them closely • Important role in nerve cells • e.g. Ach

18. Phospholipids • Lipid transport • Stomach • Breaks fat into tiny particles for digestion (i.e. lingual lipase) • Intestine • Continues emulsifying fat (i.e. bile) • Blood • Coat the surface of the lipoproteins that carry lipid particles to their destinations in the body

19. Phospholipids • Emulsifiers (Lecithin) • In body • Phospholipid with choline  phosphotidylcholine • In food • Blend of phospholipids with different nitrogen-containing components • Used as emulsifiers (e.g. salad dressing, chili, sloppy-joe mixes, and chewing gum).

20. Phospholipids • Phospholipids in food • Occur naturally in plants and animals • Examples: Egg yolks, liver, soybeans, peanuts • Not dietary essential because the body can make it

21. Sterols • A category of lipids that include cholesterol • Structural characteristics: • Multiple ring structure • Contain no fatty acids

22. Sterols • Cholesterol functions: • Structural component of cell membranes • Precursor to other substances • Examples: Vitamin D, Sterol Hormones, Manufacture bile salts • Cholesterol synthesis in liver • Sterols in food • Found only in animal foods

23. Lipid Digestion • Digestion of triglycerides (TG), cholesterol, and phospholipids (PL) • Mouth • Chewing + lingual lipase • Stomach • 30% Triglycerides + gastric lipase  FFA and DG

24. Lipid Digestion (cont.) • Small Intestine • Emulsified by bile • Rest of the “exposed” TG and DG are digested by pancreatic lipase • Phospholipids digested by pancreatic phospholipase • Cholesterol ester digested by cholesterol esterase • Bile salts surround digested fat and form micelles

25. Lipid Absorption

26. Lipid Digestion (cont.) • Micelles carry digested fat through the watery environment to microvilli/small intestine • The lipid components are then absorbed into the intestinal cells at the microvilli • Bile salts return to the liver to be used again • Short-chain FA and glycerol are directly absorbed into your intestinal cells without the help of micelles.

27. Lipids Absorption • To travel in the bloodstream, lipids are packaged into lipoprotein carriers • How? • In your intestinal cell: MG + FFA rejoin  TG • Cholesterol esters and phospholipids form here also • Then, TG, PL, cholesterol esters join protein carrier  lipoprotein. • Lipoprotein leaves the intestinal cell chylomicron goes to lymph system  bloodstream.

28. Lipid Digestion and Absorption(Figure 6.21)

29. Chylomicron Transport • In the blood stream, chylomicrons are large, fatty lipoproteins (90% fat)  circulate in the body while releasing TG • When reaching capillaries, lipoprotein lipase “attacks” chylomicrons to remove TG  FFA and glycerol: • FFA enter adipose cells  reassembled into TG • OR FFA enter muscle cells  used for energy • Glycerol  liver or kidney • Your liver picks up “left-over” chylomicron and uses them to build VLDL

30. Lipids in the Body • Very-low-density lipoproteins (VLDL): • Deliver triglycerides to cells • Intermediate-density lipoproteins (IDL) • Returns to liver and is converted to LDL • Low-density lipoproteins (LDL) • Deliver cholesterol to cells, which body uses to synthesize membranes, hormones, etc. • Returns to liver afterwards • High-density lipoproteins (HDL) • Pick up cholesterol for removal or recycling

31. Lipoprotein Pathway Summary

32. Lipoprotein density • Lipoproteins differ by size, density, and composition of their lipid cores • In general, larger the lipoprotein, the less dense it is. • Size: HDL < LDL < IDL < VLDL < Chylomicron

33. Problem Set 6, Q#4: • Describe the differences between LDL and HDL and protein composition

34. Lipids in the Diet • Recommended intake: • Reduce saturated fat and trans fat • Total fat: 20-35% of calories • Less than 10% of calories from saturated fat

35. Lipids in the Diet • Essential FA requirements • Linoleic acid/omega-6 FA should provide about 2% of calories • Requirements for omega-3 FA is less well-known • Omega-6 and omega-3 FA balance • Ratio of 6:1 (omega-6 to omega-3 FA) • While omega-3 FA is good for you, consuming too much of the omega-3 FA can suppress immune function and prolong bleeding time

36. Lipids and Health • Following are examples are diseases associated to high intakes of saturated and trans fat. • Obesity • Determined by excessive accumulation of body fat leading to a body weight in relation to height that is significantly greater than some accepted standard. • High-fat diets promote weight gain • Heart Disease/Cardiovascular Disease • Leading cause of death in US (1 death/minute) • Major risk factors • High blood cholesterol (High LDL, low HDL) • Smoking • High blood pressure

37. Lipids and Health • Atherosclerosis • Slow, progressive hardening and narrowing of arteries • Promoted by high blood cholesterol • Inflammation and atherosclerosis • How? • Smoking, infection, or high blood pressure can speed up this process described above

38. Atherosclerosis

39. AHA diet and lifestyle recommendations: • Reducing heart disease risk (pg. 222-226) • Go over on your own • 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 • Be physically active • Avoid use of and exposure to tobacco products

40. AHA diet and lifestyle recommendations (cont.): • Reducing heart disease risk (pg. 222-226) • 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, especially oily fish, at least 2/week • Limit your intake of saturated and trans fat

41. AHA diet and lifestyle recommendations (cont.): • Reducing heart disease risk (pg. 222-226) • Minimize your intake of beverage foods with added sugars • Choose and prepare foods with little or no salt • If you consume alcohol, do so in moderation • Follow the AHA recommendations when eating outside of the home

42. Metabolic Syndrome • ¼ US adults has metabolic syndrome • Has at least 3 of the following symptoms: • Excess abdominal fat • High blood glucose • High serum triglycerides • High blood pressure • Low HDL cholesterol

43. Putting it all together • Healthy People 2020 objectives target: • Reducing deaths from heart disease and stroke • Reducing the number of adults with high blood cholesterol levels

44. Cancer • Stages of development: • Initiation: a mutation in cell’s genetics  abnormal cell • Promotion: when a chemical (e.g. carcinogen) encourages initiated cells to become active • Reversible stage • Progression: when promoted cells multiply and invade healthy tissues

45. Cancer (cont.) • Dietary and lifestyle factors for reducing cancer risk: • Maintain a healthful weight • Adopt a physically active lifestyle • Consume a healthy diet • If you drink alcohol, limit consumption