Kin110_Chapter 5 Lipids.docx

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Simon Fraser University
Biomedical Physio & Kines
BPK 110
Gina Whitaker

Kin110 Chapter 5 Lipids: Fats, Phospholipids & Sterols Sources of fat in our diets Animal sources-meat, cheese, dairy Plant sources-plant oils, nuts, avocados Hidden dietary fat-French fries, pizza, pasta dishes, baked goods, salad dressings Why do we like to eat fat? Provide flavor, texture and aroma to foods Lipids-a class of nutrients that is commonly called fats -chemically they contain carbon, hydrogen, and oxygen, and most of them dissolve poorly in aqueous solutions -hydrophobic/lipophillic Classes of Lipids Triglycerides (90% of our dietary fats)-the major type of lipid in food and the body, consisting of three fatty acids attached to a glycerol molecule Phospholipids-the type of lipid whose structure includes a phosphorous atom Sterols (Cholesterol & plant sterols)-the type of lipid with a structure composed of multiple chemical rings Triglycerides Consist of three carbon molecule glycerol with three fatty acids attached to it Fatty Acids A chain of carbon and hydrogen molecules with a methyl group at one end and an acid group at the other end Classification of Fatty Acids Length of the carbon chain Degree of saturation-number of hydrogen atoms to carbon atoms Location of double bonds Isometric forms Fatty Acids are key building blocks Chain length anywhere from 4-24 carbons Most common in food are 18 carbon fatty acids Saturated vs. Unsaturated Fatty Acids Saturated-all single bonds between carbons Unsaturated-missing bonds of hydrogen Monounsaturated-one carbon-carbon double bond Polyunsaturated-more than one carbon-carbon double bond Shorter chains typically have more liquid than longer chains Location of the double bond is important Measured from the methyl (omega) end to the location of the first double bond Essential vs. non-essential fatty acids Essential fatty acids cannot be made in the body, so they are essential in the diet Example: omega-3 and omega-6 fatty acids Non-essential fatty acids can be made by the body, so they are not essential in the diet Example: omega-9 fatty acids Essential Fatty Acids Omega-3 Polyunsaturates Alpha-linoleic acid -flaxseed, Canola oil, nuts Eicosapentanoic acid (EPA) Docosahexanoic acid (DHA) -fatty fish, nuts, fortified products EPA and DHA are not essential however; if the body does not have alpha-linoleic acid, then EPA and DHA become essential Omega-6 Polyunsaturates Linoleic acid -corn oil, safflower oil, soybean oil, nuts, poultry, egg yolk Arachidonic acid -not essential however; if the body does not have linoleic acid, then Arachidonic acid becomes essential Saturated vs. Unsaturated Fats in Foods Saturated Fats-not essential therefore take in small amounts Animal fats (red meat, butter, cheese, whole milk), cocoa butter, palm oil, coconut oil Unsaturated Fats Oils (e.g. olive, canola, corn, peanut, sunflower, soybean, fish), nuts Unsaturated fats are less stable possibly making it toxic for your body when heated to high temps Geometrical Organization of Fatty Acids-Cis vs. Trans fats In unsaturated fatty acids, the 2 hydrogen atoms that surround the carbon-carbon double bond can be arranged in one of two ways Cis-hydrogens on the same side of the double bond, kinking the chain Trans-hydrogens on opposite side of the double bond Trans-fat (Trans-fatty acids) Uncommon in nature Small amounts naturally occur in dairy products Created when unsaturated fatty acids are partially converted to saturated fatty acids by the industrialized process of hydrogenation Increases shelf life Most dangerous dietary fat Look for hydrogenated oils in ingredients list Hydrogenation-a process whereby hydrogen atoms are added to the carbon-carbon double bonds of unsaturated fatty acids, making them saturated Nutrition labels in Canada-Trans Fats If a product has less than 0.2 grams of trans fat and less than 0.5 g of saturated fat, the food manufacturer can say that the product is trans-fat-free Healthiest to least healthy dietary fats Polyunsaturated (Omega 3-fats) Monounsaturated Polyunsaturated (Omega 6-fats) Saturated fats Industrialized = trans-fat Phospholipids Structure-glycerol + 2 fatty acids + phosphate group Functions Component of cell membranes Lipid transport as part of lipoproteins Emulsifiers-allow water and oil to mix Food sources-egg yolks, liver, soybeans, peanuts Cholesterol-a sterol, produced by the liver and consumed in the diet, which is needed to build cell membranes and make hormones and other essential molecules Unnecessary from the diet Found in cell membrane, myelin (insulation that surrounds nerves) Used to synthesize other sterols -vitamin D, bile acids, cortisol, testosterone, estrogen Dietary Sources: animal products 1 egg = 200mg cholesterol All the cholesterol is found in the egg yolk Should limit cholesterol intake to <300mg/day Plant Sterols-a compound found in plant cell membranes that resemble cholesterol in structure Present in small amounts in most plant food sources Can help reduce cholesterol levels in the body Studies show that plant sterols mimic cholesterol in the small intestine and partly block cholesterol absorption Lipid Digestion & Absorption A small amount of lipid digestion occurs in the stomach due to lipases produced in the mouth and stomach. These particular lipases work best on the triglycerides present in milk and so are particularly important in infant whose diet consists of entirely milk The liver produces bile which is stored in the gallbladder and released into the small intestine to aid in the digestion and absorption of fat The pancreas produces the enzyme pancreatic lipase which is released into the small intestine to break down triglycerides into monoglycerides, fatty acids, and glycerol In the small intestine, the products of fat digestion and bile form molecules, which move close enough to the microvilli to allow lipids to diffuse into the mucosal cells Inside the mucosal cells, fatty acids and monoglycerides are reassembled into triglycerides and incorporat
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