Lipids Chapter 5 BIOL 1400 Dr Mohamad H

Lipids Chapter 5 BIOL 1400 Dr. Mohamad H. Termos

Lipids: Generalities - 2 -4 T of plant oil - Fatty fish twice a week or soybean, canola or walnut oil - Minimize saturated fat, cholesterol and trans fat - Food and Nutrition Board suggests fat can be up to 35% of total calories - Do not dissolve in water - Fats are solid at room temperature - Oils are liquid at room temperature

Fatty acids: the simplest form of lipids Saturated fatty acids - Solid at room temperature - Mostly animal fats - Saturated fats in milk are suspended in liquid Unsaturated fatty acids: - Contain at least 1 double bond so at least 2 carbons are not saturated - Mono-unsaturated FAs (1 double bond): Found in canola and olive oils. - Poly-unsaturated FAs or polys (2 or more double bonds): Found in corn, soybean, sunflower, safflower oils.

Triglycerides - Most common fat/oil found in foods - Most fats in the body are TG however they are transported attached to proteins - Structure – Glycerol backbone with three fatty acids attached. – Monoglyceride has 1 FA attached to the glycerol – Diglyceride has 2 FA attached to the glycerol - Most fats are absorbed as monoglycerides and free fatty acids

Phospholipids - Glycerol backbone with 2 FAs and one compound containing phosphorous - Participate in fat digestion - Body is able to produce them - Lecithin is a phospholipid - Phospholipids: made in the liver. Make bile which is an emulsifier important in fat digestion. Also form important part of cell membranes (phospholipid bilayer)

Sterols - Waxy substances that do not dissolve in water - Cholesterol is an example - Cholesterol: function as hormones, vitamin D, cell membranes component, and in lipoproteins. The liver makes what the body needs

Fat percentages of various foods - Fat dense means more than 60% of kcal come from fat - Foods containing approximately 100% of energy as fat, very energy dense – – Salad oils Butter Margarine (does less damage to heart than butter) Mayonnaise

Fat percentages of various foods - Foods containing approximately 80% fat – Nuts – Avocados – Bacon - Foods containing approximately 75% fat – Peanut butter – Cheddar cheese

Fat percentages of various foods • Foods containing approximately 40% to 60% fat – Meats – Doughnuts • Major lipids and food examples – Saturated fatty acids: Animal fats – Unsaturated/essential fatty acids: Plant oils – Phospholipids: Egg yolks, wheat germ, peanuts, soybeans, and organ meats – Cholesterol: found only in animal Foods

Fat in Food • • • Low-fat means less than 3 g of fat per serving Fat-free means less than 0. 5 g fat per serving Reduced-fat means 25% less fat than the reference food

Fat digestion and absorption Stomach - Lipase enzyme act on triglycerides and break them down into fatty acids Small intestine - Lipase released from pancreas digests most Triglycerides - Bile, an emulsifier, is released from the gallbladder Bile suspends fats in the watery digestive juices so the enzymes can break them down Absorption: - Short- and medium-chain fatty acids travel through the portal vein to the liver - The more typical long-chain fatty acids enter circulation via the lymphatic system

Carrying lipids in the bloodstream - Since water and fat don't mix, fats must be specially packaged in Lipoproteins to travel through the body - Dietary fats are carried by Chylomicrons (a lipoprotein) - Chylomicrons enter the lymphatic system - Chylomicrons have a water-soluble shell - Chylomicrons are carried to the bloodstream - An enzyme, lipoprotein lipase, attached to the walls of the blood vessels breaks down the TG into Glycerol and FA - Cells in the immediate area absorb the FA, Glycerol goes back to the liver – Adipose cells tend to store the FA – Muscle cells can use the FA as immediate energy - Chylomicron remnants travel back to the liver and are repackaged into other lipoproteins and bile

Carrying lipids in the bloodstream Liver – Takes up lipids from the blood – Manufactures lipids and cholesterol – Synthesizes lipoproteins and releases them into the blood Very-low-density lipoproteins (VLDL) – Rich in TG so they are not dense – Carries lipids made by liver to cells

Carrying lipids in the bloodstream • Low-density lipoproteins (LDL) – Carries cholesterol made by liver and other sources to cells – Provides body cells with cholesterol and protein required for cell growth and synthesis of cell membranes and hormones • High-density lipoproteins (HDL) – High proportion of protein makes it the most dense – Carries cholesterol away from the arteries and back to the liver.

Carrying lipids in the bloodstream "Good" and "Bad" cholesterol - When too much LDL (bad) circulates in the blood, it can slowly build up in the inner walls of the arteries that feed the heart and the brain. And this may lead to the formation of plaque - Cardiovascular risk increases with low HDL - Women tend to have high HDL especially before menopause - If LDL is not cleared from the blood stream it is taken up by scavenger cells (WBCs) in the arteries - This leads to build up of cholesterol in the blood vessels - Diets low in Sat fat, trans fat and cholesterol increase uptake of LDL by the liver decreasing atherosclerosis

Carrying lipids in the bloodstream - HDL cholesterol is known as the “good” cholesterol, because high levels of HDL seem to protect against heart attack. - HDL removes excess cholesterol from arterial plaque, thus slowing its buildup.

Development of cardiovascular disease - Occurs slowly, plaque build up can begin in childhood - Associated with inadequate blood circulation from plaque build up - Myocardial infarction (heart attack) – – Blood flow surrounding the heart is interrupted Irregular or cessation of heart beat

Development of cardiovascular disease • Cerebrovascular accident (CVA, brain) – Blood flow to part of the brain is interrupted – Part of the brain may die – Also called stroke

Atherosclerosis - Development of plaque - Plaque formation increases likelihood of clots forming - 95% of all heart attacks are caused by these clots - First develops to repair damage of a vessel lining that can be caused by smoking, diabetes, hypertension, LDL or infections - Oxidized LDL contributes to plaque – Antioxidants in food (not supplements) can reduce oxidation of LDL and reduce plaque build up – Vit E supplementation may help

Broader roles for fatty acids and triglycerides - Providing energy for the body – Fatty acids are the main fuel for muscles at rest and during light activity - Storing energy – – Stored mainly as triglycerides Adipose cells are 80% lipid and 20% water and protein - Insulating and protecting the body - Aid in absorption of fat soluble Vitamins