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LIPIDS: OILS AND FATS Downloaded from higheredbcs.wiley.com/legacy/college/grosvenor/1118161742/ppt/ch05.pptx Copyright © 2014 John Wiley & Sons Canada, Ltd Copied under provision of the Copyright Act Sources of dietary fats • Animal sources: meat, cheese, dairy • Plant sources: vegetable oils, nuts, avocados • “Hidden” dietary fat: French fries, pizza, pasta dishes, baked goods, salad dressings Types of lipids • Lipids: a group of organic molecules, most of which do not dissolve in water • Lipids include: • Triglycerides: made up of fatty acids and glycerol • Fatty acids are chains of carbon atoms with an acid group at one end of the chain • They determine the triglyceride’s function in the body • Phospholipids: their structure includes a phosphorus atom • Sterols: structure composed of multiple rings Triglycerides and fatty acids a. A triglyceride contains glycerol and three fatty acids. The carbon chains of the fatty acids vary in length from short-chain fatty acids (4 to 7 carbons) to medium-chain (8 to 12 carbons) and long-chain fatty acids (more than 12 carbons). The types of fatty acids in triglycerides determine their texture, taste, physical characteristics, and actions in the body. Triglycerides and fatty acids © Can Stock Photo Inc./ angelsimon Oils are fats that are liquid at room temperature. The properties of the fatty acids in vegetable oil allow it to remain a liquid. The amounts and types of fatty acids in the triglycerides of chocolate allow it to remain brittle at room temperature, snap when bitten into, and then melt quickly and smoothly in your mouth. © iStockphoto.com/peepo Triglycerides and fatty acids • Saturated fats: carbon atoms are bonded to as many hydrogen atoms as possible; no carbon to carbon double bonds • Plentiful in animal foods, such as meat and dairy products • Plant oils are generally low in saturated fatty acids • Long-chain saturated fats: • implicated in the development of cardiovascular disease • associated with increased levels of LDL (“bad”) cholesterol in the blood Triglycerides and fatty acids • Medium-chain saturated fats: • behave differently • may have more beneficial effects • • • • shorter, relatively water-soluble quickly digested and absorbed into the blood stream bypass peripheral fat tissue less likely to be stored as fat Triglycerides and fatty acids • Unsaturated fatty acids: contain one or more carbon-carbon double bonds • Monounsaturated fatty acids: one double bond • Found in a variety of foods such as meat, olive oil, avocados, and nuts • Historically have been thought to be cardioprotective • Believed to lower LDL cholesterol • More research required to clear health effects Triglycerides and fatty acids • Polyunsaturated fatty acids: more than one double bond • Found mainly in plant sources Triglycerides and fatty acids Essential fatty acids Fatty acid composition of food Essential fatty acids • Humans are unable to synthesize fatty acids that have double bonds in the omega-6 and omega-3 positions • Therefore linoleic acid (LA) (omega-6) and alphalinolenic acid (ALA) (omega-3) are considered essential fatty acids (EFAs) and must be consumed in the diet Essential fatty acids • Important for the formation of membrane phospholipids, for fertility, red blood cell structure, metabolism, etc. • Used to make regulatory proteins called eicosanoids • Omega-3 eicosanoids reduce inflammation, lower blood pressure and have other health benefits Trans-fat (trans-fatty acids) • Small amounts occur naturally in dairy products • Created when unsaturated fatty acids are partially converted to saturated fatty acids by the industrialized process of hydrogenation • Some double bonds converted from cis to trans configuration • Decrease the rancidity and increase shelf life • Most health endangering dietary fats Trans fatty acids a. The orientation of hydrogen atoms around the double bond distinguishes cis fatty acids from trans fatty acids. Most unsaturated fatty acids found in nature have double bonds in the cis configuration. Trans fatty acids b. Small amounts of trans fatty acids occur naturally, and larger amounts are generated by hydrogenation. In 2007, Health Canada called on food manufacturers to voluntarily reduce the amount of trans fat in their products to less than 5% of total fat, which the majority of manufacturers have now complied with. Dietary lipid recommendations • The dietary reference intake (DRIs): • Total fat: 20%–35% of total calories • 30–40% for ages 1–3 & 25–35% for ages 3–18 • Adequate intake for linoleic acid = 12 g per day for women and 17 g per day for men • Adequate intake for alpha linolenic acid = 1.1.g per day for women and 1.6 g per day for men • Cholesterol, saturated fat, and trans fats: keep intake to minimum Dietary fat and cancer • Cancer is a leading cause of death in Canada • Research indicates that the risk of cancer may be decreased by choosing diets: • high in fruits, vegetables, antioxidants and omega-3 fatty acids • low in trans fats (more studies needed to determine the association between trans fats and some cancers) COPYRIGHT Copyright © 2014 John Wiley & Sons Canada, Ltd. All rights reserved. Reproduction or translation of this work beyond that permitted by Access Copyright (The Canadian Copyright Licensing Agency) is unlawful. Requests for further information should be addressed to the Permissions Department, John Wiley & Sons Canada, Ltd. The purchaser may make back-up copies for his or her own use only and not for distribution or resale. The author and the publisher assume no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information contained herein.