The Lipids: Triglycerides, Phospholipids, and Sterols

Introduction Poor health Too much fat Too little fat Too much of some kinds of fat Family of lipids Triglycerides (fats and oils) Most abundant in food and body Phospholipids Sterols

Triglycerides

Triglycerides

Triglycerides

Phospholipids Phospholipids Soluble in fat and water Emulsifiers in food industry Promote mixing of oil and fats in watery solution Lecithin is a phospholipid Food sources Eggs, liver, soybeans, wheat germ and peanuts Roles Part of cell membranes Emulsifiers

Sterols Sterols (most famous is cholesterol) Food sources Meats, eggs, fish, poultry and dairy products Cholesterol is found almost exclusively in animals Roles of sterols Body compounds made from cholesterol Bile acids Sex hormones Adrenal hormones Vitamin D

Lipid Digestion

Emulsification of Fat by Bile

Hydrolysis of a Triglyceride

Enterohepatic Circulation of Bile

Absorption of Fat

Lipid Transport

Dietary Fats Dietary fats more strongly influence the incidence of coronary heart disease (CHD) Research indicates that the type of fat is more important than the total amount of fat consumed

Dietary Fats Plasma Lipids and CHD Plasma cholesterol may arise either from diet or from endogenous biosynthesis Cholesterol is transported between the tissues in combination with protein and phospholipids as lipoproteins Lipoprotein structure (chylomicron) ApoA, ApoB, ApoC, ApoE (apolipoproteins); T (triacylglycerol); C (cholesterol); green (phospholipids)

1. Low density lipoprotein (LDL) and high density lipoprotein (HDL) Dietary Fats Plasma Lipids and CHD 1. Low density lipoprotein (LDL) and high density lipoprotein (HDL) The level of plasma cholesterol is not precisely regulated, but rather varies in response to the diet Elevated levels of LDL cholesterol result in an increased risk for CHD Elevated levels of HDL cholesterol result in a decreased risk for CHD Abnormal levels of plasma lipids (dyslipidemia) act in combination with smoking, obesity, sedentary lifestyle, insulin resistance and other risk factors to increase the risk of CHD

2. Beneficial effect of lowering plasma cholesterol Dietary Fats Plasma Lipids and CHD 2. Beneficial effect of lowering plasma cholesterol Clinical trials have demonstrated that dietary or drug treatment of hypercholesterolemia is effective in decreasing LDL, increasing HDL, and reducing the risk for cardiovascular events Diet induced changes are typically 10-20% decrease in cholesterol Treatment with statin drugs decreases plasma cholesterol by about 30-60% - HMG-CoA-reductase inhibitors

Dietary fats and plasma lipids Triacylglycerols (TAGs) are quantitatively the most important class of dietary fats The influence of TAGs on blood lipids is determined by the chemical nature of their constituent fatty acids Absence or presence of double bonds Number of double bonds (saturated vs. mono- and polyunsaturated) Location of the double bonds (ω-6 vs. ω-3) Cis vs. trans configuration of the unsaturated fatty acids

Dietary fats and plasma lipids 1. Saturated fat Triacylglycerols composed primarily of fatty acids whose hydrocarbons chains do not contain any double bonds Consumption is positively associated with high levels of total plasma cholesterol and LDL cholesterol, and an increased risk of CHD Main sources are Dairy and meat products Some vegetable oils such as coconut and palm

Dietary fats and plasma lipids 1. Saturated fat Chain lengths of 14C (myristic) and 16C (palmitic) are most potent in increasing serum cholesterol Stearic acid (18C) found in many foods including chocolate has little effect on blood cholesterol

Dietary fats and plasma lipids 2. Monounsaturated fats TAGs containing primarily fatty acids with one C=C When substituted for saturated fatty acids, lowers both total plasma cholesterol and LDL cholesterol, but maintain or increase HDL cholesterol Diets rich in olive oil (high in monounsaturated oleic acid) show a low incidence of CHD (e.g. Mediterranean cultures)

Dietary Fats Mediterranean Diet

Dietary fats and plasma lipids 3. Polyunsaturated fats (PUFAs) Triacylglycerols containing primarily fatty acids with more than one C=C Effect on cardiovascular disease is influenced by the location of the C=C within the molecule

3. Polyunsaturated fats (PUFAs) Dietary Fats 3. Polyunsaturated fats (PUFAs) ω-6 Fatty acids Long chain PUFAs with the first C=C beginning at the 6th bond position when starting from the CH3 end of the fatty acid molecule Consumption of fats containing ω-6 PUFAs, principally linoleic acid, 18:2(9,12), obtained from vegetable oils, lowers plasma cholesterol when substituted for saturated fats Lowers plasma LDL and HDL

3. Polyunsaturated fats (PUFAs) Dietary Fats 3. Polyunsaturated fats (PUFAs) ω-6 Fatty acids Linoleic acid is an essential fatty acid 5-10% of total calories recommended

3. Polyunsaturated fats (PUFAs) Dietary Fats 3. Polyunsaturated fats (PUFAs) ω-3 Fatty acids Long chain PUFAs with the first C=C beginning at the 3rd bond position from the CH3 end Suppress cardiac arrthymias, reduce serum TAGs, decrease the tendency for thrombosis, lower blood pressure, and substantially reduce the risk of cardiovascular mortality, but have little effect on LDL or HDL cholesterol levels Found in plants, principally α-linolenic acid (essential fatty acid)

3. Polyunsaturated fats (PUFAs) Dietary Fats 3. Polyunsaturated fats (PUFAs) ω-3 Fatty acids Included in infant formulas to promote brain development A deficiency of essential fatty acids is characterized by scaly dermatitis, hair loss and poor wound healing 0.6-1.2% of total calories recommended

Dietary fats and plasma lipids 4. Trans fatty acids Do not occur naturally in plants but in small amounts in animals Formed during the hydrogenation of liquid vegetable oils e.g. in the manufacture of margarine and partially hydrogenated vegetable oil Elevate serum LDL but not HDL

High-Fat Foods and Heart Disease

High-Fat Foods and Heart Disease

Other dietary factors affecting CHD Dietary Fats Other dietary factors affecting CHD Moderate consumption of alcohol (e.g. 2 drinks a day) decreases the risk of CHD, because there is a positive correlation between moderate alcohol consumption and the plasma concentration of HDL Because of the potential dangers of alcohol abuse, health professionals are reluctant to recommend increased alcohol consumption to their patients Red wine contains phenolic compounds that inhibit lipoprotein oxidation These antioxidants are also present in raisins and grape seed

Recommended Intakes of Fat Dietary Guidelines Diet low in saturated and trans fat Diet low in cholesterol 20 to 35 percent of daily energy from fat

Butter and Margarine Labels Compared The closer the “partially hydrogenated oils” is to the beginning of the ingredients list, the more trans fat it contains