Lipids Basic Human Nutrition Lecture 4 Elisabeth Strachan

Lipids n n n Family of compounds that includes triglycerides, phospholipids, and sterols. Fats are solids are room temperature; oils are liquids at room temperature. Excess energy is stored in the body as fat (triglycerides). 2

Lipids continued n n n Serve as energy reserves. Cushion the vital organs. Protect the body against temperature extremes. Carry fat soluble nutrients Serve as raw materials. Provide the major material of which cell membranes are made. 3

Fats n n Provide more energy per gram than carbohydrate or protein. Enhance food’s aroma and flavour. Contributes to tenderness of meats and baked goods. Contribute to satiety or a feeling of fullness after a meal. 4

Triglycerides are the body’s chief storage form of fat. n n Composed of 3 fatty acids and 1 molecule of glycerol. Glycerol is a small water soluble CHO derivative. Fatty acids differ in 1) the length of their carbon chain & 2) the bonding of carbon atoms and the arrangement of hydrogen along the carbon chain. 5

Fatty Acids n n Short chain fatty acids have 4 to 8 carbons (dairy fats). Medium chain fatty acids have 8 to 12 carbons (palm oil & coconut oil). Long chain fatty acids have 16 to 18 carbons (many animal fats). Diet composed mainly of long chain fatty acids from animal sources. 6

Saturated versus unsaturated n n n Saturation refers to the number of hydrogens a fatty acid chain is holding. If every carbon atom in the chain has a hydrogen, the chain is saturated. A carbon chain with one or more points of hydrogen atoms missing is unsaturated. The degree of saturation determines hardness or softness of fats. 7

Unsaturated fats n n One point of unsaturation along carbon chain = monounsaturated fat, e. g. , olive oil. Two or more points of unsaturation = polyunsaturated fat e. g. , safflower oil. Animal fats are saturated fats. Palm oil and coconut oil are saturated vegetable fats. Other plant oils are unsaturated. 8

Phospholipids n n n Similar to a triglyceride but has a phosphate group and choline in place of one of the fatty acids. The phosphorus makes it soluble in water and its fatty acid makes it soluble in fat. Therefore it can act as an emulsifier and keep the fat dispersed in water. Phospholipids are also important in blood clotting & in the insulating sheath around nerve fibers. 9

Phospholipids n n n The best known phospholipid is lecithin. Lecithin & other phospholipids assist fats to travel back and forth across the lipid containing membranes of cells into the watery fluids on both sides. They enable fat-soluble substances (vitamins and hormones) to pass easily in and out of cells. 10

Sterols n n n Compounds containing a four-carbon ring structure with a variety of side chains attached. Many important body compounds are sterols. Cholesterol is “the most famous sterol”. It is a compound the body makes and uses. The liver makes about 800 -1500 mg of cholesterol/day. 11

Cholesterol is a fatty-like substance. n n Cholesterol’s harmful effect occurs when it forms deposits in the artery walls. Major sources are from animal foods or it is synthesized by the body. Egg yolk is a major source of cholesterol. Saturated fat raises blood cholesterol more than dietary cholesterol. 12

Digestion & Absorption of Fats n n n Lipids tend to separate from the watery fluids of digestion. Bile from the liver emulsifies lipids. Enzymes are then able to breakdown lipids to monoglycerides and fatty acids. 13

Chylomicrons n n The class of lipoproteins that transport lipids from the intestinal cells to the rest of the body. The chylomicrons are only 1 of several clusters of lipids and proteins that are used as transport vehicles for fats. 14

Lipid Transport n n n The body makes 4 main types of lipoproteins: Chylomicrons are the largest and least dense. They transport mostly triglycerides from the intestine (via the lymph) to the rest of the body. Very low-density lipoproteins (VLDL) which carry triglycerides and other lipids. Made in the liver. Transports lipids to the tissues. Low-density lipoproteins (LDL) which are made from VLDL after they have donated much of their fat to body cells. Composed primarily of cholesterol. High-density lipoproteins (HDL) which carry cholesterol from body cells to the liver. Composed primarily of protein 15

“Good” cholesterol/ “bad” cholesterol n n n LDL’s (bad cholesterol) which carry almost 50% of total cholesterol has the greatest affinity for arterial walls. High LDL is associated with higher risk of heart attack. High LDL’s contributes to plaque formation on artery walls. Hence, “bad. ” 16

Good cholesterol-HDL protects against heart disease n n Acts as a scavenger of cholesterol removing it from arterial wall and transporting it to liver where it is incorporated into bile and excreted via intestines. Competes with LDL fragment for receptor sites on arterial wall, thus blocking entrance of LDL into cell wall. 17

Essential Fatty Acids n n n The body can synthesize all fatty acids except these. These 2 polyunsaturated fatty acids are required for basic body functions. Both provide raw materials for hormone-like substances that regulate: blood pressure, blood clotting, blood lipids, the immune response, the inflammation response to injury and infection & others. 18

Essential fatty acids continued n n n Serve as structural parts of cell membranes. Constitute a major part of lipids in the brain and nerves. Are essential to normal growth. 19

Essential Fatty Acid Linoleic Acid - Omega 6 n n n Sources: leafy vegetables, seeds, nuts, grains, vegetable oils (corn, safflower, soybean, cottonseed, sesame, sunflower). Primary member of omega 6 fatty acid family. Body can convert linoleic acid to other members of this family. Omega 6 play a critical role in the cell membranes that define and protect each cell of the body. 20

Essential Fatty Acid Linolenic Acid – Omega 3 n Sources: Fats and oils (canola, soybean, walnut, wheat germ, margarine made from canola and soybean oil. Nuts & seeds (flaxseed, walnuts, soybeans kernels); shellfish and fish (mackerel, salmon, bluefish, tuna, mullet, lake trout & others). 21

Linolenic acid- omega 3 continued n n n Make up a large portion of the brain’s cerebral cortex and are required for its development. Help to form the eye’s retina and are required for development of normal vision. Are converted to hormone-like substances that affect the heart and immune system. 22

Processing of fats Hydrogenation: n Adding of hydrogen to vegetable oils to improve shelf life, plasticity (hardness/spreadability). n Stability at high temperatures in cooking. 23

Trans fats n n n Fatty acids with hydrogens on opposite sides of the double bond. They may elevate LDL cholesterol and lower HDL. Sources: fast foods, baked goods, commercially prepared foods, margarines. 24

Trans Fats n n Act like saturated fats in the body Most found in commercially prepared foods n some French fries, potato chips, donuts, cookies, crackers, cereals, shortening, muffins, pizza crusts, buns, cakes 25

Naturally Occurring Trans Fats n n n Found in dairy and meat products Some are not the same as those found in processed foods One type is conjugated linoleic acid (CLA) n These may reduce risk of cancer and heart disease. 26

Fat and cardiovascular disease n n n High blood cholesterol is a strong risk factor for heart disease. Dietary cholesterol has little impact on blood cholesterol. Saturated fat significantly increases blood cholesterol. 27

Risk factors for heart disease Modifiable: n High cholesterol n High blood pressure n Cigarette Smoking n Obesity n Diabetes n Physical Inactivity Non-Modifiable: n Increasing age, gender, family history. 28

Syndrome X/ Metabolic Syndrome/Insulin resistance syndrome Low HDL, high blood pressure, insulin resistance and abdominal obesity along with: high blood triglycerides comprise a cluster of health risks known as the metabolic syndrome. 29

1990 Nutrition Recommendations for fat n n n No more than 30% of energy as fat. No more than 10% as saturated fat. Health Canada recommends an intake of total omega-3 fatty acids at a level of at least 0. 5% of energy and an intake of total omega-6 fatty acids of at least 3% of energy. 30

Fat replacers Ingredients that replace some or all of the functions of fat and may or may not provide energy. Conventional ingredients used in different ways: n Add water or whip air into foods. n Add fat-free milk to creamy foods. n Use lean meats and soy protein to replace high-fat meats. n Bake foods instead of frying them. 31

Artificial fats n n n They are fat replacers that offer the sensory and cooking qualities of fats, but none of the kcalories. Olestra appears to have same properties as fats and oils when used in cooking, frying and baking and tastes very much like real fat. Olestra may cause abdominal cramping and loose stools and inhibits the absorption of some vitamins and other nutrients. 32

Fat - Part of a Healthy Diet 20 – 35% of total Calories from fat 2000 Calorie diet = 44 – 78 grams of fat Or 11 – 19 ½ teaspoons. n 1500 Calorie diet = 33 – 58 grams of fat Or 8 ¼ – 14 ½ teaspoons. n 33

Where is fat found? 1. Easy to see n Fat added to foods n n Butter, margarine, oil Fat on the outside of foods n Chicken skin, outside trim on meat 2. Hidden n Ingredient n n Snack foods, baked products, desserts Added in cooking n Fried foods, cream soups, sauces 34

Types of Fat n n All fat-containing foods have a mixture of different fats Types of fats include: n n Polyunsaturated fats (PUFA) Monounsaturated fats (MUFA) Saturated fats (SFA) Trans fats (TFA) 35

Nutrition Claims Nutrient Content Claims Fat free – none or hardly any fat (less than 0. 5 grams of fat per amount) Low fat – a small amount (less than 3 grams of fat per amount) Light – can be used on foods that are reduced in fat or Calories compared to the original version 36

Nutrition Claims Health Claim Example: A healthy diet low in saturated and trans fats may reduce the risk of heart disease. (Name of food) is low in saturated and trans fats. 37

Ingredient List n Look for types of fat n n n Vegetable oils Tropical oils (palm, coconut) Hydrogenated or partially hydrogenated oils Shortening or margarine Animal fats/lard Butter 38

Lower-fat Cooking Tips 1. 2. 3. Broil, bake, barbecue, roast, microwave, stir-fry or brown in a non-stick pan. Brown ground meat or poultry in a pan or microwave in a plastic sieve and drain off fat before adding other ingredients. Refrigerate stews, soups, chilies and meat sauces and remove hardened fat that rises to the surface. 39

Recommended Intakes of Fat n n Linoleic acid AI (omega 6) n 5% - 10% of energy intake Linolenic acid AI (omega 3) n 0. 6 - 1. 2% of energy intake 40 Copyright 2005 Wadsworth Group, a division of Thomson Learning

Mediterranean Diet n n n Diets focus on: crusty breads, whole grains, potatoes, pastas, variety of vegetables, legumes, feta and mozzarella cheeses, yogurt, nuts, fruits. Fish, seafood, poultry, a few eggs and little meat is eaten. Principle sources of fat are olives, olive oil, nuts and fish. 41

Mediterranean Diets are: n n n Low in saturated fat. Very low in trans fat. Rich in unsaturated fat. Rich in complex carbohydrate and fibre. Rich in nutrients and phytochemicals that support good health. 42