FATS - Understanding Food PDF

FATS Floris van Dyck, Still-Life with Fruit, Nuts and Cheese (1613) NATS1560 UNDERSTANDING FOOD For class use only. Do not circulate.  LEARNING OBJECTIVES To name the different kinds of lipids and identify the kinds that are important for nutrition To explain the molecular composition...

FATS Floris van Dyck, Still-Life with Fruit, Nuts and Cheese (1613) NATS1560 UNDERSTANDING FOOD For class use only. Do not circulate.  LEARNING OBJECTIVES To name the different kinds of lipids and identify the kinds that are important for nutrition To explain the molecular composition of triglycerides and distinguish the different types of fatty acids To list the functions of fats in the body To list the main food sources of the different kinds of fats, and explain the difference between fats and oils in terms of different melting points To explain what hydrogenated and trans fats are To define rancidity and distinguish between lipolytic and oxidative rancidity 2  LIPIDS Triglycerides (or triacylglycerols) – fats and oils in food and in adipose tissue of our body – commonly called “fats” if solid at room temperature, “oils” if liquid Phospholipids − building blocks of cell membranes in food and in our body Steroids – cholesterol, vitamin D, steroid hormones (estrogens and androgens) Waxes – resins, beeswax, paraffin, In nutrition, “lipids” is often used to refer either to triglycerides etc. only, or to triglycerides, – indigestible phospholipids, and steroids. 3  TRIGLYCERIDES A molecule of triglyceride is formed by the bonding of one glycerol molecule and three fatty acids molecules molecular “building blocks” of triglycerides = glycerol and fatty acids Different triglycerides contain different combinations of fatty acids Most fats are mixtures of different triglycerides Glycerol and fatty acids are Different fats are distinguished from the molecular one another by the building blocks prevalent fatty of triglycerides acids that they contain Source: Sizer and Whitney, Nutrition: Concepts and Controversies (2008), 149 4  methyl end carboxy l end or FATTY ACIDS or ω (omega) end α O H H H H H (alpha) end H O C C C C C C H H H H H H A molecule of fatty acid is formed by a chain of carbon atoms − to which hydrogen atoms are attached − with a carboxyl group (-COOH) at one end and a methyl group (-CH3) at the other endare short (4-6), medium (6-14), There tran s and long-chain (16-22) fatty acids The carbon atoms can form single or cis double bonds with each other double carbon-carbon ‒ in cis or trans configuration 5 bonds  TYPES OF FATTY ACIDS Saturated fatty acid (SFA) – carbon chain with single carbon-carbon bonds only Palmitic acid, a long-chain (16- carbon) saturated fatty acid, one of the most common fatty acids in food double Unsaturated fatty acid (UFA) bond ω  monounsaturated (MUFA) – one double carbon-carbon bond Oleic acid, a 18-carbon, ω-9  polyunsaturated (PUFA) monounsaturated fatty acid, the most common fatty acid in food – multiple double carbon-carbon bonds Essential fatty acids – alpha-linolenic acid (omega-3) Alpha-linolenic acid, an essential ω-3 (ALA) polyunsaturated fatty acid – linoleic acid (omega-6) 6  FATTY ACID COMPOSITION OF FOOD FATS Most food fats contain mixtures of SFAs, MUFAs and PUFAs A food fat is commonly (but inaccurately) called saturated or unsaturated (mono- or poly-) when it is high in the corresponding type of fatty acids Source: Sizer and Whitney, Nutrition: Concepts and 7 Controversies (2008), 149 THE FUNCTIONS OF FATS IN THE BODY Concentrated source of energy Energy storage Storage and transport of fat-soluble vitamins Sources of essential fatty acids (needed for cell membranes, body tissues and bones, immune system, and more) Body insulation Protection of inner organs Palatability of food and satiety 8  FOOD SOURCES OF FATS AND OILS Saturated Unsaturated Meat, suet, lard monounsaturated butter, whole milk olives and olive oil and partially peanuts, canola oil skimmed (2% and avocado 1%) milk and milk polyunsaturated products fish and other coconut oil, palm oil seafood nuts and seeds other vegetable oils: soybean, canola, corn, sunflower, sesame, etc. 9 THE MELTING POINT OF FATS All fats contain mixtures of saturated and unsaturated fatty acids The type of fatty acids that are prevalent give Above 28 ⁰C butter the fat its physical melts. characteristics The presence of SFAs, especially long-chain ones, raises the melting point of the fat Oils are fats that are liquid a room temperature − i.e., have melting points lower than room Below 4 ⁰C olive oil temperature solidifies. 10  REVIEW What are the functions of fats in the body? What are the main food sources of the different kinds of fats? What is the difference between saturated and unsaturated fats at the molecular level? How can you distinguish saturated from unsaturated fats in your kitchen? 11  ARE SATURATED FATS BAD FOR YOU? Since the 1970s, official dietary advice brands saturated fats as “bad fats” and recommends limiting them in your diet The new Canada’s Food Guide (2019) emphasize even more strongly the message that saturated fats are unhealthy, hence to be avoided Yet, recent metastudies have reported that there is no scientific evidence to support this advice There seems to be no expert consensus on this question 12  HYDROGENATION Hydrogenation: industrial process to turn unsaturated fatty acids into saturated – exposure to H at high temperature and pressure in presence of a catalyst – it breaks double carbon bonds and saturates the fatty acids with hydrogen The food industry used partially hydrogenated fats to make margarine and vegetable shortening, and to improve the texture and prolong the shelf life of processed foods, such as cookies 13  ARTIFICIAL TRANS FATTY ACIDS A side effect of Cis partial isomer hydrogenation is the production of Trans artificial trans-fatty H acids H isomer C C These industrial by-products H raise the risk of heart disease, inflammation, type- C C 2 diabetes, and possibly cancer H 14 CIS AND TRANS FATTY ACIDS Most unsaturated fatty acids are in the cis form. A few trans fatty acids are naturally present in milk. But industrially processed foods may contain trans fatty acids that are artificially made! 15 © A. Brown, Understanding Food. Principles & Preparation  TRANS FATS Trans fats are fats that contain trans Artificial trans fatty acids fatty acids, which can be natural or artificial − lower the level of “good Natural trans fatty acids are found in cholesterol” (HDL) and raise small amounts in milk and dairy the level of bad cholesterol products, beef, and lamb (LDL) in the blood Artificial trans fatty acids are formed − raise the risk of heart disease, during industrial processing of foods inflammation, type-2 − unavoidably in small amounts during diabetes, and possibly cancer the refining of some vegetable oils, Since early 2000, mandatory such as canola and soybean oil labelling of trans fats in food − mostly from partially hydrogenated products fats As of 2018 in Canada, partially hydrogenated fats are classified as contaminants and adulterating substances, and are banned from food 16  RANCIDITY Lipolytic rancidity – microbes produce an enzyme (lipase) that breaks triglycerides into short fatty acids – characteristic flavours of butter and cheese Oxidative rancidity – unsaturated fatty acids become oxidized – release of free radicals, which damage cells, proteins, and DNA, and may cause aging and diseases – rancid smell and taste 17  REVIEW What is hydrogenation? What are trans fats? How are artificial trans fats produced and why do they end up in your food? What are the two kinds of rancidity? 18