Lipids

1. Lipids Zeina Ghossoub El-Aswad, MSc

2. NATURE • Compounds (fats, oils, waxes..) insoluble in water, soluble in organic solvents (ether, chloroform, benzene..) • Lipids include triglycerides 95% (fats and oils), phospholipids (e.g. lecithin) and sterols (e.g. cholesterol)

3. Nature • Fatty acids (FA): • -FA comprise two parts: • Hydrocarbon chain (R): hydrophobic • Acid group: hydrophilic • Info: There are 24 common FA, most have 4 to 22 C-atoms

4. Nature -Fat (triglycerides) is the body’s chief storage form for excess energy consumed -Fat is stored in specialized cells called fat cells that have the ability to enlarge almost indefinitely. Fat surrounding the internal organs serves as shock absorber.

6. Nature -The fat blanket under the skin (adipose tissue) serves as an insulating layer, assisting with internal climate control. -Fat is also part of all cell membranes. Vitamin A, D, E, and K are only soluble/found in fat-rich foods.

7. Nature • Fat contributes to taste and sensory appeal of foods. • Fat slows digestion and provides satiety.

8. Triglycerides

9. Triglycerides • Triglycerides (Fats and oils): Animal and plant origin • Most TG contain a mixture of more than 1 type of fatty acids. --- Depending on the nature of the fatty acids attached, the resulting fat can be liquid or solid at room temperature. Diglycerides: 1 Glycerol + 2 F.A. Monoglycerides: 1 Glycerol + 1 F.A.

10. Fatty Acids: • -Fatty acids are organic acids that comprise of 2 parts. Acid group (COOH) Hydrocarbon chain (R) (hydrophilic) (hydrophobic)

11. Fatty Acids -Very few are found as such in the body or in foods. Usually, they are part of TG molecules. -  Fatty acids have an even # of carbon atoms in their hydrocarbon chain (between 4-22) Fatty acids may be saturated(SFA) or unsaturated {presence of double bond: mono(MUFA), poly (PUFA)}

12. Fatty Acids • Fatty acids vary in (1) the length of their hydrocarbon chain, (2) their degree of unsaturation and (3) the location of their double bond.  • Fatty acid chain length and saturation affects TG’s physical characteristics and storage properties (solid vs. liquid). • The more saturated the fat, the more solid it is

13. Fatty Acids • In general, vegetable and fish oils are rich in PUFA -- while animal fats are the most saturated

14. FA of the 3 and 6 families • TWO essentialpolyunsaturated fatty acids: Linoleic acid (ω-6) & Linolenic acid (ω-3) cannot be synthesized in the body and hence need to be supplied from the diet. They:  • -Serve as structural parts of cell membranes • -Constitute a major part of the lipids of the brain & nerves • -Are essential to normal growth in infants/children • -Transformed into hormone-like substances important for vital body functions: blood pressure, blood clot formation, the immune & inflammation responses, etc…

16. Health benefits of (ω-3) fatty acids Lower blood cholesterol and thus heart attack & stroke • Prevent blood clot formation • May lower blood pressure Make up a large portion of the brain and thus may lower incidence of depression

17. Firmness and stability of fats • The degree of unsaturation influences the firmness of fats as well as their stability and shelf life. • Polyunsaturated vegetable oils are liquid at room temperature and less stable than the more saturated animal fats. • Polyunsaturated fats become rancid because their double bonds are unstable and thus react with atmospheric oxygen, a process called autoxidation.

18. Hydrogenation • A chemical process by which hydrogens are added to fatty acids double bonds. Unsaturated fats are more prone to oxidation due to the instability of the double bond. Unsaturated Saturated

19. Hydrogenation • Advantages: -Renders the oil more stable and resistant to oxidation, hence a longer shelf life Alters the texture of foods (spreadable: margarine)

20. Hydrogenation • Disadvantages Makes polyunsaturated fats more saturated, consequently less healthy Produces trans[PL2]fatty acids that behave more like saturated fats than unsaturated! (thus LDL)

21. Phospholipids • Lecithin: best-known phospholipid • Phospholipids are naturally occurring in egg-yolks, liver, soybeans and peanuts. 1 glycerol + 2 Fatty Acids + Phosphate group Hydrophobic end Hydrophilic end

22. Role Play a role in keeping fats dispersed in water: Important constituents of cell membranes Can be made by the body, hence is NOT an essential nutrient Contribute 9 Cal/g

23. Sterols • Compounds with a multiple-ring structure. • 1.Cholesterol • 2.Sex hormones (testosterone & estrogen) • 3.Adrenal hormone (cortisol) • 4.Bile emulsifier important for fat digestion

24. Sterols • Cholesterol is the starting material for the synthesis of all the above compounds. It is also a structural component of brain and nerve cells.

25. Cholesterol • Cholesterol: is synthesized in the liver of humans (endogenous) as well as obtained from animal products in the diet (exogenous). • However, our body makes enough cholesterol and thus there is no need to get extra cholesterol through the diet. • NOTE:Food cholesterol does NOT raise blood cholesterol as dramatically as saturated fat does!

26. Cholesterol • Cholesterol in the blood is transported in two forms: 1.LDL: transports cholesterol from the liver to tissues 2.HDL: transports cholesterol from tissues back to the liver (returns cholesterol to the liver) Factors that increase HDL: exercise, estrogen, and moderate alcohol intake. Factors that increase LDL: smoking, obesity, sedentary life style, and saturated fat intake

27. Cholesterol • Cholesterol’s harmful effects on the body occur when it forms deposits in the artery walls: atherosclerosis Strokes Heart attacks • Heart disease is the #1 killer of adults in the USA. And blood cholesterol concentration is one of the 3 major risk factors for CVD, along with smoking and hypertension.

28. Lipid digestion and transport • Mouth: • Lingual lipase: important in milk fat digestion in infants, little importance in adults. • Stomach: • Little fat digestion takes place in the stomach

30. Lipid digestion and transport • Small intestine: • Bile (made by the liver and stored in the gall bladder) mixes the fat particles with the watery medium by emulsification (micelle formation) allowing pancreatic lipase to act on splitting the TG molecules. After digestion, fats are reassembled as TG molecules (water insoluble) that get transported in the blood (water soluble) as part of lipoproteins.

31. Fat in the diet • Visible fat: butter, oil, mayo, fat trimmed from meat. • Invisible fat: milk, cheese, pastries, fried food, fat in the marbling of meat. • SFA: • Found mainly in animal products: beef, chicken, pork and dairy.

32. Fat in the diet • MUFA: • Oleic acid is the most common. Found mainly in olive oil, canola oil, olives, avocados, almonds and walnuts. • PUFA: • Found in vegetable seeds and fish. • Cholesterol: • Cholesterol-rich foods are eggs, shellfish, red meats, liver, and dairy products.

33. BODY NEEDS • Total fat intake should contribute no more than 30% of daily total calories, divided equally between SFA, MUFA and PUFA (10% each). • Dietary cholesterol recommendation is ~ 300 mg/day from diet. • NOTE: Excess fat consumption can lead to obesity, CVD, and certain types of cancers

34. Alcohol • The alcohol produced for human consumption is ethanol. It is a liquid derived from the fermentation of sugars in fruits, vegetables and grains. -Beer: 4-5% alcohol (the rest is water) -Wine: 12-14% alcohol • Whiskey, Rum, Gin, Vodka: 40-45% alcohol

35. Alcohol • 12 oz Beer = 4 oz Wine = 1.25 oz Liquor = ½ oz pure ethanol • (1 bottle)=(1 wine glass)=(1 shot glass) • Proof: is a measure of the alcohol content in a beverage and is double the percentage. (e.g. an 86-proof bottle of whiskey is 43% alcohol)

36. Alcohol • Alcohol does not need digestion; it can directly be absorbed by the stomach and reach the brain within a minute!! • Alcohol is metabolized by the liver. As the blood circulates, the liver of an average adult male will metabolize about 1/3 oz of alcohol per hour – somewhat less than the amount of alcohol in one drink!

37. Alcohol • Thus, consumption of alcohol at a rate > 1 drink/hr accumulation of alcohol in the blood.  Ethanol is a TOXIN. Brain cells are particularly sensitive to excessive exposure to alcohol. The brain shrinks even in people who only drink moderately. Abstinence, together with good nutrition, reverses the brain damage. However, heavy drinking can lead to severe and irreversible harm to vision, memory, and learning ability.  • --Alcohol yields 7 Cal/g of “Empty Calories”--

38. Alcohol • Tips on drinking alcohol: -Drink only in moderation. -Drink slowly. Pace yourself (< 1 drink/hr). -Eat before drinking. Food slows alcohol’s absorption, especially CHO and fat snacks. -Add ice or water to drinks to dilute them. -Alcohol will make you thirsty, so alternating alcoholic beverages with non-alcoholic ones will quench your thirst. Otherwise, each drink may worsen the thirst. -Avoid salty snacks, they will make you thirstier.