The Lipids: Triglycerides, Phospholipids, and Sterols Chapter 5

Introduction Poor health Family of lipids Too much fat Too little fat Too much of some kinds of fat Family of lipids Triglycerides Phospholipids Sterols

Chemist’s View of Fatty Acids and Triglycerides Energy provided per gram More carbons and hydrogens Preview of lipids Triglycerides: glycerol and 3 fatty acids Fatty acids: even number of carbons Fatty acids: saturated or unsaturated Omega-3 and omega-6 fatty acids

Chemist’s View of Fatty Acids and Triglycerides Organic acid Methyl group at one end; acid group at other end Usually even number of carbons 18-carbon fatty acids abundant in food Saturations Saturated – full of hydrogens Unsaturated – missing hydrogens

Chemist’s View of Fatty Acids and Triglycerides Location of double bonds Nearest the methyl end of the carbon chain Omega number Linolenic acid Monounsaturated fatty acids Omega-9 groups

Chemist’s View of Fatty Acids and Triglycerides Glycerol backbone Three fatty acids Formed via series of condensation reactions Usually contain mixture of fatty acids

Chemist’s View of Fatty Acids and Triglycerides

Chemist’s View of Fatty Acids and Triglycerides

Chemist’s View of Fatty Acids and Triglycerides Degree of unsaturation Firmness Polyunsaturated fats Saturated fats Length of carbon chain Stability Oxidation and spoilage of fats

Chemist’s View of Fatty Acids and Triglycerides Degree of unsaturation Hydrogenation Advantages Trans-fatty acids Configurations – cis and trans Similarity to other types of fat

Chemist’s View of Fatty Acids and Triglycerides

Chemist’s View of Fatty Acids and Triglycerides

Chemist’s View of Phospholipids and Sterols Solubility in fat and water Emulsifiers in food industry Lecithin Food sources Roles Part of cell membranes Emulsifiers

Chemist’s View of Phospholipids and Sterols Food sources Cholesterol Plant sterols Roles of sterols Body compounds made from cholesterol

Lipid Digestion Fats are hydrophobic Goal of fat digestion Digestive enzymes are hydrophilic Goal of fat digestion Dismantle triglycerides Monoglycerides, fatty acids, and glycerol

Lipid Digestion

Lipid Digestion Mouth Stomach Lingual lipase Strong muscle contractions Gastric lipase

Lipid Digestion Small intestine Bile routes Cholecystokinin (CCK) Gall bladder releases bile Bile acts as emulsifier Pancreatic lipase Hydrolysis Triglycerides and phospholipids Bile routes Blood cholesterol levels

Emulsification of Fat by Bile

Hydrolysis of a Triglyceride

Enterohepatic Circulation of Bile

Lipid Absorption Directly into bloodstream Lymphatic system Glycerol and short- & medium-chain fatty acids Lymphatic system Micelles diffuse into intestinal cells Reassembly of triglycerides Packed with proteins – chylomicrons Bypass liver at first

Absorption of Fat

Lipid Transport Four main types of lipoproteins Chylomicrons Largest and least dense Transport diet-derived lipids Liver removes remnants from blood Very-low-density lipoproteins (VLDL) Made in the liver Proportion of lipid shift

Lipid Transport Health implications Four main types of lipoproteins Low-density lipoproteins (LDL) Cell needs Liver regulation High-density lipoproteins (HDL) Remove cholesterol from cells Carry cholesterol to liver for recycling Anti-inflammatory properties Health implications

Lipid Transport

Role of Triglycerides Provide the cells with energy Adipose tissue 9 kcalories per gram Virtually unlimited ability to store fat energy in body Adipose tissue Secretes hormones Adipokines Skin insulation, shock absorption, cell membranes, and cell signaling pathways

Essential Fatty Acids Linoleic acid – Omega-6 fatty acid Sources Linolenic acid – Omega-3 fatty acid DHA EPA Eicosanoids Fatty acid deficiencies

A Preview of Lipid Metabolism Adipose cells store fat after meals Lipoprotein lipase Hydrolyzes triglycerides Triglycerides reassembled inside adipose cells Using fat for energy Protein sparing Energy deprivation Fasting and ketone bodies

Health Effects of Lipids Heart disease Elevated blood cholesterol Saturated fat – increase LDL cholesterol, promote blood clotting Dietary choices Trans-fats – increase LDL cholesterol Dietary cholesterol

Health Effects of Lipids Heart disease Monounsaturated fats Replace saturated and trans fats Reduces blood cholesterol Dietary sources Omega-3 fats Benefits Omega-6 to omega-3 ratio

Health Effects of Lipids Cancer Promotion rather than initiation of cancer Dietary fat and cancer risk Differs for various types of cancer Obesity Cutting fat from diet reduces kcalories Dietary recommendations

Recommended Intakes of Fat DRI and Dietary Guidelines Diet low in saturated and trans fat Diet low in cholesterol 20 to 35 percent of daily energy from fat AI set for linoleic and linolenic acids Daily Values (DV) on food labels Saturated fat and cholesterol Risk of insufficient fat intake

From Guidelines to Groceries Fat-soluble vitamins A, D, E, and K Flavor, texture, and palatability Meats and meat alternatives Selections Milk and milk products

From Guidelines to Groceries Vegetables, fruits, and grains Lowers consumption of various fats in the diet Invisible fat Fried and baked goods Choose wisely Unprocessed foods

From Guidelines to Groceries Fat replacers Types Risks Read food labels Total fat, saturated fat, trans fat, and cholesterol Compare products % Daily Value vs. % kcalories from fat

Butter and Margarine Labels Compared

High-Fat Foods – Friend or Foe? Highlight 5 High-Fat Foods – Friend or Foe?

Guidelines for Fat Intake Limit saturated fat and trans fat intake Moderate kcalories Enough fat for good health Not too much of the harmful fats DRI recommendations Compatible with low rates of disease

High-Fat Foods and Heart Health Olive oil Benefits for heart health Replace saturated fats Nuts LDL cholesterol Fat composition Cautious advice for dietary inclusion

High-Fat Foods and Heart Health Fish Omega-3 fatty acids Benefits for heart health Environmental contaminants Dietary recommendations

High-Fat Foods and Heart Health

High-Fat Foods and Heart Disease Saturated fat and LDL cholesterol Sources of saturated fat in the U.S. Meats Whole milk products Tropical oils Zero saturated fat is not possible Trans fat Limit hydrogenated foods

High-Fat Foods and Heart Disease

High-Fat Foods and Heart Disease

High-Fat Foods and Heart Disease

The Mediterranean Diet Traditionally Low in saturated fat Very low in trans fat Rich in unsaturated fat Rich in complex carbohydrate and fiber Rich in nutrients and phytochemicals Benefits for heart disease risk