Fat: Sources, Functions, and Requirements PDF

FAT: SOURCES, FUNCTIONS AND REQUIREMENTS  TOPIC LEARNING OUTCOME At the end of this lecture, the students should be able to:- 1. Differentiate types of lipids and their functions in the body. 2. Describe the physiological roles of lipids. 3. Identify sources of fats and recommended i...

FAT: SOURCES, FUNCTIONS AND REQUIREMENTS  TOPIC LEARNING OUTCOME At the end of this lecture, the students should be able to:- 1. Differentiate types of lipids and their functions in the body. 2. Describe the physiological roles of lipids. 3. Identify sources of fats and recommended intake levels. 4. Understand the impact of fats on health, including essential fatty acids, trans fats, and cholesterol.  OUTLINE What are lipids? What are the key functions of lipids? Sources of fats Requirements and recommended intakes of fats Lipids and Food Technology Deficiencies and Excesses WHAT ARE LIPIDS?  WHAT ARE LIPIDS? A family of compounds that includes 1. Triglycerides (fats & oils) Fats: lipids that are solid at room temperature Oils: lipids that are liquid at room temperature 2. Phospholipids 3. Sterols (cholesterol) Contain carbon, oxygen, and hydrogen Hydrophobic  WHAT ARE LIPIDS? Fatty Acids – Building blocks for triglycerides and phospholipids – A chain of carbon and hydrogen atoms with a carboxyl group at the alpha end and a methyl group at the omega end  WHAT ARE LIPIDS? Higher ratio of carbon and hydrogen to oxygen than in carbohydrates and protein – 9 kilocalories per gram of fat 20 different fatty acids with varied length, saturation, double bond location and shape  WHAT ARE LIPIDS? Structure of fatty acids  WHAT ARE LIPIDS? Length – Short-chain fatty acids Two to four carbons Weak attraction Liquid at room temperature – Medium-chain fatty acids Six to ten carbons  WHAT ARE LIPIDS? Length – Long-chain fatty acids 12 or more carbons Most common type of fatty acid in foods Strong attraction Solid at room temperature  WHAT ARE LIPIDS? Saturation – Saturated All the carbons on the fatty acid are bound to hydrogen Solid at room temperature Higher melting point  WHAT ARE LIPIDS? Saturation – Unsaturated Some carbons on fatty acid form a double bond with each other instead of binding to hydrogen Monounsaturated fatty acids (MUFA) – Has one double bond – Found mostly in vegetable oils such as olive, canola & peanut  WHAT ARE LIPIDS? Saturation – Unsaturated Polyunsaturated fatty acid (PUFA) – Has two or more double bonds Liquid at room temperature Lower melting point  WHAT ARE LIPIDS? Saturated and Unsaturated Fatty Acids Help Shape Foods Figure 5.3  WHAT ARE LIPIDS? Double Bond Location – The location of the first double bond in unsaturated fatty acids effect the omega-3 fatty acid and omega-6 fatty acid – n-3 fatty acid First double bond is between the third and fourth carbon from the omega end Example: Alpha-linolenic acid (ALA) – One of the two essential fatty acids  WHAT ARE LIPIDS? Double Bond Location – n-6 fatty acid First double bond is between the sixth and seventh carbon from the omega end Example: Linoleic acid (LA) – One of the two essential fatty acids WHAT ARE LIPIDS? n-3 fatty acid n-6 fatty acid Figure 5.4  WHAT ARE LIPIDS? Shape – Unsaturated fatty acids form two different shapes  WHAT ARE LIPIDS? Rancidity: spoiling of fats through oxidation – More double bonds therefore more susceptible to oxidation and rancidity PUFA > MUFA > Saturated fatty acids Enhancing stability of fatty acids by reducing rancidity – Adding antioxidants – Limiting food exposure to oxygen, heat, and light – Hydrogenation  WHAT ARE LIPIDS? Triglycerides – the major class of dietary lipids, including fats & oils – made up of 3 units known as fatty acids and 1 unit called glycerol (backbone) – Comprise about 95% of lipids in food and the human body  WHAT ARE LIPIDS? Three fatty acids connected to a glycerol backbone Portion of Figure 5.7  WHAT ARE LIPIDS? Functions – Add texture – Makes meats tender Caution: – Preserves freshness High levels in – Stores as adipose tissue the blood are a risk factor for energy for heart disease  WHAT ARE LIPIDS? Phospholipids – 2nd of three main classes of lipids – similar to a triglyceride, but contains phosphorous – hydrophilic on one end; hydrophobic on the other – make up the phospholipid bilayer in the cell membrane – Lecithin (a.k.a. phosphatidylcholine) a major phospholipid in the cell membrane used as an emulsifier in foods – Synthesized by the liver  WHAT ARE LIPIDS? Phospholipids  WHAT ARE LIPIDS? Sterols – 3rd of three main classes of lipids; – More complex than phospholipids or triglycerides Four connecting rings of carbon and hydrogen – Do not provide energy – Cholesterol is the best known sterol Found in every cell in the body Helps with numerous body processes – Phytosterols – major plant sterols  QUICK REVIEW Fatty acids – carbon and hydrogen chain, carboxylic acid, methyl group – basic structural units of triglycerides and phospholipids – differ in chain length, degree of saturation, double bond location and shape Saturated fatty acids: no double bonds Monounsaturated fatty acids: one double bond Polyunsaturated fatty acids: two or more double bonds  QUICK REVIEW Fatty acids – Essential fatty acids Lenoleic Alpha-linolenic acid – Food manufactures hydrogenate or add antioxidants to fatty acids to reduce susceptibility to rancidity Triglycerides – Found in the body – Stored in the adipose tissue – Major source of energy  QUICK REVIEW Phospholipids – An important part of cell membrane structure – Lecithin Important to cell membrane Used as a food emulsifier Sterols – Do not contain fatty acids – Do not provide energy WHAT ARE THE KEY FUNCTIONS OF LIPIDS?  WHAT ARE THE KEY FUNCTIONS OF LIPIDS? Source of energy Form body structures Regulate metabolism Enhance absorption of fat-soluble vitamins Provide insulation to help regulate body temperature Cushion major organs  WHAT ARE THE KEY FUNCTIONS OF LIPIDS? 1. Fat is used as energy – Provides concentrated source of kilocalories 9 kilocalories per gram – Readily available when the body needs energy – Body has an unlimited ability to store excess energy as fat in adipocytes Fat cells have the capacity to enlarge as much as 1,000 times their original size Body has the ability to produce additional fat cells  WHAT ARE THE KEY FUNCTIONS OF LIPIDS? Fat is used as energy and helps absorb lipid compounds – Preferred source of energy for the heart, liver, and muscles – Cannot sustain life alone – Needs glucose Only glycerol can be used for gluconeogenesis – Several essential nutrients require dietary fat for absorption – 20 grams per day are needed to stimulate chylomicrons that transport fat-soluble vitamins  WHAT ARE THE KEY FUNCTIONS OF LIPIDS? 2. Fat helps insulate and protect – Fat in subcutaneous tissue Insulates body Maintains body temperature – Fat protects bones and vital organs from trauma Too much fat eliminates the protective benefit  WHAT ARE THE KEY FUNCTIONS OF LIPIDS? 3. Essential fatty acids, eicosanoids, and cell membrane – LA can be elongated and converted to arachidonic acid (polyunsaturated omega-6 fatty acid) – ALA Converts to eicosapentaenoic acid (EPA) – EPA elongates to docosahexaenoic acid (DHA) Needed for healthy cell membranes  WHAT ARE THE KEY FUNCTIONS OF LIPIDS? – EPA and arachidonic acid are used to manufacture eicosanoids – Eicosanoids are hormonelike substances Prostaglandins, thromboxanes, and leukotrienes, lipoxin Regulate the immune system, blood clotting, inflammation, and blood pressure  WHAT ARE THE KEY FUNCTIONS OF LIPIDS? Cholesterol – A structural part of the cell membrane – A precursor to vitamin D – A precursor to bile acid – Precursor for sex hormones such as estrogen and testosterone  QUICK REVIEW Fat – An energy-dense source of fuel – Cushions and protects bones, organs, and nerves – Helps maintain body temperature – Provides essential fatty acids – Is needed for the absorption of fat-soluble vitamins and carotenoids  QUICK REVIEW Essential fatty acids are precursors to EPA and DHA which manufacture Regulate the immune system – Prostaglandins Regulate blood clotting – Thromboxanes Regulate inflammation – Leukotrienes Regulate blood pressure Essential functions of cholesterol – Is part of cell membrane – Is needed to make Vitamin D Bile acid Sex hormones SOURCES OF LIPIDS  SOURCES OF LIPIDS Dietary fats can be divided into two categories: – visible fats cooking oils that are plant-based (vegetable oils) table spreads, which may be either plant-based (margarines) or animal fats (butter). – invisible fats natural constituents of edible biological material ranging from cereals, vegetables, fruits, pulses, nuts and oilseeds, dairy products, meat, eggs or seafood Figure 5.20  SOURCES OF LIPIDS Palm oil – main cooking oil for most Malaysians, as this country is a primary – has an almost equal amount of saturated and unsaturated fatty acids as indicated by 40% of palmitic acid (C16:0), 4% of stearic acid (C18:0) and 43% of oleic acid (C18:1). Figure 5.20  SOURCES OF LIPIDS Palm oil – By consuming palm olein alone, at 30%TEI, an individual ingests : Sufficient LA (3-4%TEI EFA) 12%TEI SFA and 14%TEI MUFA as well as other micronutrients such as vitamin A and E Figure 5.20  SOURCES OF LIPIDS Coconut oil – one of the major sources of SFA in the Malaysian diet- SANTAN For instance, nasi lemak, curry and cendol – contains 92% of SFA with the major fatty acids being lauric acid and myristic acid. Figure 5.20  SOURCES OF LIPIDS Vegetable oils – such as soybean and corn oils are the mains sources of the EFAs linoleic acid (LA) and α-linolenic acid (ALA) – classified as n-6 PUFAs Figure 5.20 SOURCES OF LIPIDS SOURCES OF LIPIDS  SOURCES OF LIPIDS Fish – long chain fatty acids (LCFAs) such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids – classified as n-3 PUFAs – LCFAs commonly consumed by Malaysians are Indian mackerel (kembong), anchovies, yellow-tail fish, tuna, sardines, torpedo scads, Indian and short-fin scads, pomfret, red snapper, king mackerel, marine catfish and stingray Figure 5.20 SOURCES OF LIPIDS SOURCES OF LIPIDS  SOURCES OF LIPIDS Foods containing trans fat and cholesterol? – Hydrogenated fats are used by many commercial food producers to Provide rich texture Increase shelf live Decrease incidence of rancidity – During the hydrogenation process trans fats form – Some trans fats are naturally occurring Figure 5.20  SOURCES OF LIPIDS Food sources trans-fat Figure 5.20  SOURCES OF LIPIDS Trans fat may actually be worse for heart health than saturated fats – Raise LDL cholesterol – Lower HDL cholesterol FDA requires trans fat to be listed on food labels The food industry is working to find replacements for trans fats in foods  SOURCES OF LIPIDS Food sources of cholesterol and plant sterols – Cholesterol comes mainly from animal products – The cholesterol produced in plant cell walls and oils is so minimal they are considered cholesterol free  SOURCES OF LIPIDS Phytosterols and stanols – Lower LDL levels by competing with cholesterol for absorption – Are found in soybean oil, many fruits, vegetables, legumes, sesame seeds, nuts, cereals, and other plant foods – Food manufacturers are fortifying foods with them to help lower cholesterol  SOURCES OF LIPIDS Fat Substitutes – Designed to provide the creamy properties of fat for fewer kilocalories – Fall into three categories Carbohydrate-based: Majority of fat substitutes Protein-based: Provide a creamy texture in the mouth Fat-based: Give physical attributes of fat for fewer kilocalories – Overconsumption of kilocalories from regular, low-fat, or fat-free products can lead to weight gain  QUICK REVIEW Lean meat and poultry, fish, low-fat or nonfat dairy products and limited amounts of nuts and cheese – Best sources of essential fatty acids – Limit intake of saturated and trans fats Commercially prepared baked goods and snack items – Are high in kilocalories – Are high in saturated and trans fats – Should be consumed rarely Use vegetable oils in the place of butter  QUICK REVIEW Trans fats are made by heating oil and adding hydrogen gas to saturate the carbons of the fatty acids Trans fats raise LDL cholesterol and lower HDL cholesterol Trans fats are found in many commercially prepared foods and must be listed on the food label Other oils are being tested to replace trans fats in foods Cholesterol is found mostly in animal products Phytosterols are found in vegetable oils, nuts, legumes, whole grains, fruits, and vegetables  QUICK REVIEW Fat substitutes provide the properties of fat for fewer kilocalories and grams of fat Fat substitutes can be carbohydrate based, protein based, or fat based Some substitutes such as olestra work by passing unabsorbed through the GI tract Reduced-fat and fat-free foods still contain kilocalories and should be eaten in limited amounts REQUIREMENTS AND RECOMMENDED INTAKES OF FATS REQUIREMENTS AND RECOMMENDED INTAKES OF FATS 25 to 30% TEI – Upper safe limit of 35%TEI for active adults. – Children and teenagers < 18 years: 25 to 35%TEI SFA: less than 10%TEI MUFA: 12 to 15%TEI Trans fatty acid: