Dietary Fats Lecture PDF

Kingdom of Saudi Arabia ‫اﻟﻤﻤﻠﻜﺔ اﻟﻌﺮﺑﯿﺔ اﻟﺴﻌﻮدﯾﺔ‬ 1 Ministry of Education ‫وزارة اﻟﺘﻌﻠﯿﻢ‬ Jazan University ‫ﺟﺎﻣﻌﺔ ﺟﺎزان‬ Faculty of Applied Medical Sciences ‫ﻛﻠﯿﺔ اﻟﻌﻠﻮم اﻟﻄﺒﯿﺔ اﻟﺘﻄﺒﯿﻘ...

Kingdom of Saudi Arabia ‫اﻟﻤﻤﻠﻜﺔ اﻟﻌﺮﺑﯿﺔ اﻟﺴﻌﻮدﯾﺔ‬ 1 Ministry of Education ‫وزارة اﻟﺘﻌﻠﯿﻢ‬ Jazan University ‫ﺟﺎﻣﻌﺔ ﺟﺎزان‬ Faculty of Applied Medical Sciences ‫ﻛﻠﯿﺔ اﻟﻌﻠﻮم اﻟﻄﺒﯿﺔ اﻟﺘﻄﺒﯿﻘﯿﺔ‬ Department of Clinical Nutrition ‫ﻗﺴﻢ اﻟﺘﻐﺬﯾﺔ اﻹﻛﻠﯿﻨﯿﻜﯿﺔ‬ LECTURE ? ?  1 1- Identify the fats and other lipids which are essential in the diet. 2- Describe their chemical nature and functions in the human body. 3- List the food sources of various lipids and essential fatty acids. 4- Determine how much and what type of fats should be included in our daily diet. 5- Know how the body digests, absorbs, and metabolizes fat. 6- Understand the consequences of deficient or excessive consumption of lipids.  1 1- Mouth : a- No chemical digestion takes place in the mouth. b- Fat is broken into smaller particles by chewing and is mixed with saliva. 2- Stomach : a- Peristaltic movements churn the food along with the gastric juice. b- Two enzymes help in digesting fats ( gastric lipase, in the gastric juice and pancreatic lipase from the pancreas which acts in small intestine.). In the stomach fats converts to emulsified. Gastric lipase acts on emulsified and the main digestion of fats begins in the small intestine.  1 3- Small intestine : a- In the duodenum fats stimulates the secretion of bile from the gall bladder. b- Bile acts as an emulsifier and breaks down large fats into smaller particles. This increase the total surface area of fat and increase the efficiency of enzyme action c- The alkaline nature of bile helps pancreatic lipase to remove fatty acid from the triglyceride and converting them to diglycerides and monoglycerides and finally to fatty acids and glycerol..  1 Ò The final products of fat digestion to be absorbed are fatty acids , glycerol, monoglycerides, and diglycerides. Ò Some remaining fat which is undigested may be excreted through the feces.  1 Mouth small parts mixed with saliva gastric lipase Stomach converted to emulsified bile acts Duodenum breaks down large fats into smaller particles pancreatic lipase Small intestine glycerol + monoglycerides + diglycerides 1  1 Fat absorption occurs in two ways : 1- Via hepatic portal vein : This process only occurs for some medium chain free fatty acids and monoglyceride. chain from 10 12 carbon atoms  1 2- Via Lymph system ; Ò Fatty acids and monoglycerides taken up by the mucosal cells are re- synthesized to form triglycerides. Ò This are formed into spherical chylomicrons by the addition of phospholipids, cholesterol, cholesterol esters and specific protein, apoprotein. Chylomicron is a specific type of lipoprotein formed in enterocytes. Ò In this way water-insoluble triglycerides can be transported as lipoprotein. 1 1  1 Ò After absorption fat may be oxidized by the body tissues to give ( Energy +CO2+H2O) or stored in the fat deposits. Ò Unlike carbohydrates where there is only a limited amount of glycogen stored (0.5 kg) ,amounts of fat stored can be very large and variable. Ò Carbohydrates can also be converted into fat and stored in the same way as dietary fat. Ò Fatty acids are not a major source of blood glucose but rather a source of ketone bodies which can be used as an energy source by most tissues if glucose supply is deficient.  1 Ò The fat is broken down to glycerol + fatty acids. The glycerol takes part in the glycolytic pathway and can under some circumstances be made into glucose( this is also called gluconeogenesis ). Ò Fatty acids are broken down to acetyl ( COA) Which can then either enter the (TCA) cycle or form acetoacetate in the liver by the reaction of two molecules. From acetoacetate, ketone bodies may form and are passed into blood stream and then to the body tissues.  1 Ò Most tissues except the brain can completely break down the ketone bodies to ( CO2 +H2O) in the citric acid cycle followed by the respiratory chain with the generation of (ATP). 1  1 glucose glycerol Fat pyruvate alanin fatty acid pyruvate fatty acyl acetyl COA amino acid CoA leucine ketone bodies oxaloacetate citrate citric acid cycle alpha ketoglutarate Amino acid tyrosine amino acid glutamic acid mitochondrial membrans  1 Most foods except the bread, cereal group and the vegetable fruit group (except olives and avocado) contain varying percentages of lipids. Some fats are visible such as fats and oils added to food or used for frying. Many sources are hidden or invisible such as the fats and oils naturally present in the food , milk, egg yolk, oily fish, and meat.  1 Ò Both visible and invisible sources must be taken into account while calculation the fat content of a meal. 1- Plant sources : All oils and oils seeds like groundnut, sesame, soya bean, rice bran, coconut, almond, cashew nut, corn, safflower, sunflower and all hydrogenated fats and margarine are sources of lipids.  1 2- Animal sources : Mutton , fish, poultry, milk, and milk products, such as butter cream, yoghurt, cheese, eggs, and organ meats. 3- Invisible sources : Invisible sources of fats are nuts ,salad dressings, flesh food, desserts cookies, cakes, milk, eggs, milk based sweet, which are rich in fat, but the fat is not visible.  1 Ò A deficiency of fat causes a deficiency of essential fatty acids, which are required for healthy cell membranes and their permeability. Ò A deficiency results in characteristic eczema and skin lesions. It is seen in infants as dry scaly lesions on the skin. Toad skin or dry papules are seen on upper limbs. Ò A deficiency of fat may result in a deficiency of fat-soluble vitamins and growth and weight may be affected in children.  1 Ò The percentage consumption of fat varies widely in different regions in different income groups. Ò Fats should provide 20 -25 % from the total calories. Ò Excess intake of fats causes obesity , fat stored in adipose tissue, increase blood cholesterol , and causes cardiovascular diseases while food rich in omega -3 have a protective effect  1 Ò Fat should contribute not more than 30 % of the total kcalories. Ò Kcal from saturated fat should not exceed 10 % of total calories. Ò At least 10 % calories should be provided by PUFA to ensure an adequate intake of essential fatty acids. Ò The correct ratio of omega-3 and omega-6 should be maintained. Ò Cholesterol intake should not exceed 180 mg /day.  1 Ò A variety of cooking oils should be used every day to ensure consumption of all essential fatty acids. Ò Nonvegetarians should eat groundnut, corn, soya, and olive oil throughout the year, while for fish eaters a mixture of safflower and sunflower oil is adequate. Ò Rice bran oil and corn oil is recommended for vegetarians.  1 The fat content of the diet can be reduced by following simple measures such as : 1- Use skim cow’s milk and its products. 2- Select lean meat and trim off visible fat. 3- Steam, boil, or poach food instead of frying. 4- Avoid salad dressing or use low fat dressing.  1 5- Select fruit for dessert instead of baked puddings and pastries. 6- For flavor add herbs spices and lime juice instead of fats. 7- Dry powdered chutneys of flax and niger seeds are rich in essential fatty acids.  Kingdom of Saudi Arabia ‫اﻟﻤﻤﻠﻜﺔ اﻟﻌﺮﺑﯿﺔ اﻟﺴﻌﻮدﯾﺔ‬ 1 1 Ministry of Education ‫وزارة اﻟﺘﻌﻠﯿﻢ‬ Jazan University ‫ﺟﺎﻣﻌﺔ ﺟﺎزان‬ Faculty of Applied Medical Sciences ‫ﻛﻠﯿﺔ اﻟﻌﻠﻮم اﻟﻄﺒﯿﺔ اﻟﺘﻄﺒﯿﻘﯿﺔ‬ Department of Clinical Nutrition ‫ﻗﺴﻢ اﻟﺘﻐﺬﯾﺔ اﻹﻛﻠﯿﻨﯿﻜﯿﺔ‬ 1- Identify the fats and other lipids which are essential in the diet. 2- Describe their chemical nature and functions in the human body. LECTURE ? 3- List the food sources of various lipids and essential fatty acids. ? 4- Determine how much and what type of fats should be included in our daily diet. 5-Know how the body digests, absorbs, and metabolizes fat. 6- Understand the consequences of deficient or excessive consumption of lipids 1 1 Hence, they are a more concentrated source of energy providing Fats and oils belong to a group of compounds called lipids, which are 2,1/4 times more energy than carbohydrates and proteins. insoluble in water but soluble in fat solvents. Like carbohydrates ,they are mainly made up of carbon, hydrogen, and The lipids that important to our health are fatty acids , fats , oils , oxygen. phospholipids , lipoproteins , and sterols. They contain much smaller proportions of oxygen and larger proportions of carbon and hydrogen than carbohydrates.  1 1 5-Absorption of fat-soluble vitamins : Fat is necessary for the absorption of fat-soluble vitamins A, D, E, and K. 6-Essential fatty acids : Is necessary to meet the body requirements for linoleic and linolenic acids. 1-Energy : 7-Synthesis of hormones : Is necessary for the synthesis of some Fats are a concentrated source of energy hormones ,6 hormones. 1g 9 kcal 8-Synthesis of cell membranes : Is important constituent of all cell 2-Protein sparing action :An adequate intake of fat in the diet allows membranes. proteins to perform their main functions of growth and 9-Satiety value : Fat s slow down the secretion of gastric juice and maintenance. speed of digestion. 3-Thermal insulation : Subcutaneous fat acts as an insulation and Food is more flavor, some because of volatile essential oils naturally helps in retaining body heat. present and fats used for cooking. 4-Protection of vital organs: Fat provides a protective padding to vital A well-cooked meal containing fats is more satisfying than a meal organs from mechanical shock and keeps them in place. devoid of fats. 1 1 Based on degree of saturation Lipids Lipids Fats &Oils Animal fats Marine oils Vegetables oils (solid at room temperature) cod liver oil (mainly liquid at room temperature) Butter (from milk) shark liver oil Glycerol +Fatty acids Tallow (from beef) halibut oil Suet (from sheep &oxen) whale oil Fats Oils Saturated Unsaturated Lard (from hogs) cocoa butter groundnut (no double bonds ) coconut oil sesame vanaspati sunflower Monounsaturated Polyunsaturated palm oil Rice bran palmolein corn (one double bonds) (two or more double bonds) olive cotton seed mustard Based on origin  1 1 Lipids Simple compound Derived Sterols Lipids lipids lipids Classification based on structure: (made up of 1- Simple lipids: Glycerol +3 phospholipids lipoprotein diglycerides cholesterol Fatty acids lecithin HDL monoglycerides They constitute more than 98% of food and body fats. Simple lipids are made LDL oils VLDL up of three fatty acids attached to glycerol. They are mixed triglycerides which Groundnut chylomicrons Vitamin D means that more than one type of fatty acids is present in the fat , cooking oils Fats sesame Ergosterol Butter sunflower 7- Dehydrocholesterol and butter. Cream safflower 2- Compound lipids : Hydrogenated rice bran Fat olive They are fats in which at least one fatty acids is replaced by carbohydrate Suet Lard protein, phosphorous, they are fats + non- fat molecule Tallow ( Classification of lipids based on structure ) A- phospholipids. B- Glycolipids. C- Lipoprotein which include: chylomicrons, HDL, LDL and VLDL 1 1 Ò It is a fat like substance present in food. Ò It is different in structure from triglycerides, as it has a ring structure. 3- Derived lipids : Ò It is present in all cells of the body and in large amounts in brain and nerve tissue. They are the breakdown products of fats and include : Ò Cholesterol if consumed in excess is responsible for diseases of cardiovascular A- diglycerides. B- monoglycerides system. C- glycerol D- fatty acids. Ò The normal blood cholesterol level for adults should be below 200 mg / 100 ml 4- Sterol : blood They are not made up of fatty acids and glycerol but have a benzene ring Ò The human body gets cholesterol from two sources : structure. These fat like substances include : 1- Synthesis in the liver. A- cholesterol B- fat soluble vitamins , A,D, E, and K 2- Food rich in cholesterol. If the diet is deficient in cholesterol the body can synthesize the required cholesterol..  1 Approximated cholesterol content of some common foods : 1 The function of cholesterol are: 1- Cholesterol is a precursor of all steroid hormones sex hormones. 2- A precursor of vitamin D,7- dehydrocholesterol is present in the skin which is irradiated by UV rays of sunlight to form vitamin D. 3- It is required for formation of bile. 4- It is an essential constituent of cell membranes. Cholesterol is present in animal food only. 1 1 Phospholipids : Ò They are composed of fats, phosphoric acid, and a nitrogenous base. Ò They are required for cell permeability and for the formation of brain and Glycolipids : nervous tissue. They contain glucose or galactose in place of Ò They help in transporting fats throughout the body as they form a part of the lipoproteins. one of the fatty acids in the triglyceride molecule.  1 1 Lipoproteins : Ò They include , chylomicrons, very low-density lipoproteins (VLDL), low density Ò Fatty acids consist of chains of carbon atoms with a methyl (CH3) group at one end lipoproteins (LDL),and high-density lipoproteins (HDL). and a carboxyl (COOH) group at the other end. Ò They are composed of lipids ( triglycerides, cholesterol, and phospholipids ) Ò Fatty acids may have short chains or they may have long chains (12 – 22) carbon and proteins in varying proportions with percentage of proteins being least in atoms. chylomicrons and most in high density lipoproteins (HDL). Ò They may be saturated or unsaturated. Saturated fats have single bonds between Ò They are required for transporting triglycerides to various tissues in the body carbon atoms , while unsaturated fats have one or more double bonds between via blood circulation. carbon atoms. Ò Fatty acids with two or more double bonds are called polyunsaturated. Ò LDL are the main carriers of cholesterol, an increase in LDL increases the Ò Unsaturated fatty acids are highly reactive to oxygen at the point of unsaturation risk of heart disease. and turn rancid. Ò HDL help in lowering cholesterol levels. Ò Hydrogen is added at the double bond during hydrogenation of oils. Ò An LDL, HDL ratio of less than 3 is desirable. Ò Food fats are generally a mixture of both type of fatty acids. 1 1 Fatty acids Saturated Unsaturated (no double bond) Stearic monounsaturated Palmitic (1 double bond) Myristic Oleic Polyunsaturated Butyric (2 or more double bond) Linoleic Linolenic Arachidonic (Classification of fatty acids ) 1 1 Two of the polyunsaturated fatty acids (PUFA) can not be synthesized by the body. They have to be provided in the required amount by our diet and are called essential fatty acids which included : 1- Linoleic acids ------------ Omega -6. 2- Linolenic acids ----------- Omega – 3. 1 1 * Omega – 3 fatty acid are polyunsaturated fatty acid with the end most double bond on the third carbon from the methyl end. Ò 18:3 is the abbreviation for linolenic acid which is a long chain fatty acid made up of 18 carbons with three double bond with the last double bond between carbons 3 and 4 from the methyl /omega end. Ò Omega – 3 rich foods include: Olive oil, fish, fish oils , mustard oil, soya bean, flaxseed, fenugreek seeds, nuts, nuts oils,and green leafy vegetables Ò Omega-3 fatty acid is an essential part of each and every cell membrane. It helps in maintaining the cells membrane and prevents free radicals from attacking DNA in the cell. Ò Free radicals are O, OH, CO, NO, and NOO. Ò The percentage of free radicals increase because of the following : high protein diet ,high fat diet ,stress , smoking and alcohol. *  1 1 Omega – 6 fatty acids have the last double bond located on the 6 carbon from the methyl or omega end. Ò Omega – 6 rich oils include :Safflower, sunflower, cottonseed, corn, sesame, Balance between omega-3 and omega-6 is essential for and groundnut. Ò When consumption of omega-6 goes up need for omega-3 increases. Omega-3 maintaining good health. They are beneficial for the and omega-6 in the correct ratio helps in reducing blood cholesterol level. Ò Adequate Intake (AI) for alpha-linolenic acid is 1.6 g/day for men and 1.1 cardiovascular system, for inflammatory reactions and g/day for women. Ò The AI for linoleic acid is 17 g/day for men and 12 g/day for women. immune response. 1 TRIGLYCERIDES Ò Triglycerides comprise about 95% of lipids in food and in the human body. Ò Body fat is largely composed of stored triglycerides. Ò A triglyceride has three fatty acids bonded to glycerol. Ò In a particular food, such as olives or cheese, the unsaturated and saturated fats occur in different proportions, but one type of fatty acid (SFA,MUFA, or PUFA) often predominates.