Fats notes for nursing students

notes on fat

1. Fats/lipids

2. Definition Lipids are heterogeneous group of compounds which are relatively insoluble in water soluble in organic solvents like other, benzene, alcohol, chloroform etc

3. Classification of lipids Lipids are classified into 3 major classes, based 0n their composition . Simple lipids • Compound lipids • Derived lipids 

4. Simple lipids: Simple lipids are esters of fatty acids with alcohols. They do not contain any conjugate groups . They are two types Fats/ oils Waxes Fats/oils :They are the esters of fatty acids with glycerol Waxes : Waxes are esters of fatty acids with higher alçohols . E.g.: Bee wax, carnauba wax, wool fat (lanolin),

5. Compound lipids They contain conjugate groups in addition to fatty acids & alcohols. These include phospholipids, glycolipids , sulpholipids etc .

6.   Phospholipids : These are compounds lipids containing phosphoric acid residue as conjugate group. Phospholipids are of two types, i ) Glycerophospholipids : E.g.: Lecithin, Cephalin , Plasmalogen etc ii) Sphingophospholipids : E.g.: Sphingomyelin of myelin sheath of nerves b) Glycolipids : These are compounds lipids containing carbohydrate residues . Glycolipids are two types, i ) Cerebrosides : E.g.: Kerasin , cerebron , nervon , & oxynervon ii) Gangliosides : E.g.: GM1, GM2, GM3, GM4 etc

7. Derived lipids These are the products or precursors of simple & compound lipids. Examples: Fatty acids, cholesterol, steroid hormones, fatty alcohols, Ketone prostaglandins etc,

8. Fatty acids fatty acids are the main building blocks of all simple lipids and compound lipids  Fatty acids are divided into two groups based on the nature of hydrocarbon chain i ) Saturated fatty acids ii) unsaturated fatty acids

9.  Saturated fatty acids: They do not have any double bond in their hydrocarbon chain Example: Acetic acid Propionie acid butyric acid Valeric acid Caproic acid Caprylic acid Capric acíd Lauric acid Myristicacid Palmitic acid Stearic acid Arachidic acid

10. Unsaturated fatty acids Unsaturated fatty acids have double bonds in their hydrocarbon chain. subdivided into two types based on the number of double bonds. Monounsaturated fatty acids [MUFA] b) Polyunsaturated fatty acids [PUFA):

11. Monounsaturated fatty acids [MUFA]: These contain only one double bond in their structure. Examples are palmitoleic acid, oleic acids etc. Palmitoleic acid Oleic acids Polyunsaturated fatty acids [PUFA): These contain more than one double bond in their structure. Examples are Linoleic acid - 2 double bonds Linolenic acid - 3 double bonds Arachidonic acid - 4 double bonds Timnodonic acid - 5 double bonds Cervonic acid -6 double bonds.

12. Dietary sources of fatty acids: Fatty acids are mainly present as constituents of fats/oils or compound lipids Acetic acid is present in the vinegar. Butyric acid, Valeric and Caproic acids present in butter . Lauric acid and myristic acid are present in vegetable oils (Especially in coconutand palm oil) and also in butter. Stearic acid is present in most vegetable and animal fats Palmitoleic acid is present in olive oils, fish oils and beef . Oleic acid is widely distributed in all fats and oils . Arachidonic acid, Timnodonic acid and Cervonic acid are present in fish liver oil and shell fishes Trans fatty acids are mainly present in Vanaspati,Margarines , deep dried fast foods , cake mixes, chips and crackers, whipped toppings, packaged candy, cookies doughnuts, pies and cakes etc.

13. Essential fatty acids : The fatty acids, which are not synthesized in the body, hence have to be supplied in the diet are termed as essential fatty acids Linoleic acid, - linolenic acid arachidonic acid Dietary sources: Essential fatty acids are mostly found in vegetable oils (Except coconut oil and palm and fish liver oils )

14. Essential fatty acids : Functions: Eicosanoid synthesis : Essential fatty acids serve as precursors of eicosanoids , which function as local hormones. Lipid transport : Essential fatty acids are required for the synthesis of phospholipids Lowering serum cholesterol : Essential fatty acids reduce serum cholesterol levels . Normal Epidermal growth : Essential fatty acids are required for the normal reproductive function Normal reproductive function: Essential fatty acids are required for normal epidermal growth  Deficiency Phrenoderma :It is characterized by horny papular eruptions on the posterior and lateral parts of thigh and on the back and buttocks Deficiency of EFA may also causes reproductive failure

15. Dietary sources of fats /oils Vegetable oils (Ground nut oil, coconut oil, mustard oil, sunflower oil) Vanaspati , margarines Milk and milk products like Ghee, butter, cheese Meat, fish, poultry, egg yolk etc Fats are present in almost all food articles (Except sugars) in small amounts. Visible fats are those that are separated from their natural source and visible to the naked eye. Example; cooking oils (vegetable fats/oils) from oil bearing seeds and nut,ghee and butter from milk etc. It is easy to estimate the amount of their dietary intake .   Invisible fats are hidden and are not visible to the naked eye as they found in small quantity in almost all food materials. For instance, foods like cereals, pulses, nuts, tubers contain small amounts of fats,

16. Saturated fat and unsaturated fat a) Unsaturated fats (Mainly vegetable fats): • Unsaturated fats contain relatively more of unsaturated fatty acids and less of saturated fatty acids • They are liquid or soft at room temperature.) • They have low melting points. • They are susceptible to rancidity when exposed to light and oxygen over a prolonged period. Rancidity results in an offensive taste and smell. • They are predominately found in vegetable fats/oils (with the exceptions of coconut, palm, and palm kernel oils). In contrast, fish oils, although they are termed as animalfats , contain large amounts of unsaturated fatty acids

17. Saturated fat and unsaturated fat Saturated fats (Mainly animal fats): • Saturated fats have relatively more of saturated fatty acids and less of unsaturated fatty acids • They are solid at room temperature. Exceptions to this generalization are coconut oil and palm oils (tropical oils) • They have high melting points • They are more stable than unsaturated fats. • They are predominately found in animal fat/oil, except for the coconut oil and palm oils 

18. Rancidity of fats Fats and Oils have a tendency to become rancid (stale) on standing. The term rancidity refers to the appearance of unpleasant smell and taste for fats/ oils. Two types : Hydrolytic rancidity: Is due to partial hydrolysis of triacylglycerols by the enzyme lipaes present in naturally occurring fats / oils. Oxidative Rancidity : The Oxidative Rancidity is a result of oxidation of unsaturated fatty acids (present in triglycerides) to form lipid peroxides, epoxides and aldehydes peroxidases and free radicals. These products have an unpleasant taste and odor Unsaturated fats are more susceptible to oxidative rancidity.

19. Hydrogenation Process of converting unsaturated fat to saturated fat is called  hydrogenationin the presence of catalysts like nickel or cobalt and at high temperatures, unsaturated fatty acids present in fats/oils can accept hydrogen at the double bonds and become saturated. Example:   Vanaspati is prepared mainly from hydrogenation of groundnut oil to which 5% sesame oil is added. Margarine which is used as a cheap substitution of butter mainly in western countries is prepared from hydrogenation of vegetable oils like coconut oil and ground nut oil. The heated oil is churned with skimmed milk.

20. Hydrogenation Nutritional importance of hydrogenation Hydrogenation improves the stability of a fat or oil, change its texture and increase its functionality, The main advantage of hydrogenation is it change of consistency,where the liquid vegetable oils are converted to odorless semi solid and solid fats that are easy to pack, store and transport. Since vegetable oils are deficient in vitamin A, hydrogenated fats ( vanasapai margarines) are fortified with vitamin A and D Hydrogenation also prevents rancidity. So, storage quality improves. During hydrogenation process, some of the remaining unsaturated fatty acids vegetables oils are altered from cis to trans form. The principle oil used for hydrogenation are vegetable oils (usually groundnut, corn, Soy bean, cotton seed, canola oils etc), which are rich in linolenic acid. Linolenic acid is hydrogenated to oleic acid, elaidic acid and stearic acid.

21. Refined oils Raw oils are refined in order to remove the free fatty acids and rancid materials. Refining does not bring about any change in the unsaturated fatty acid content of the oil. It only improves the quality and taste of oils . • Refined oils are free from odor and color . • Refined oils are costly . Refining usually consists of 3 processes. i ) Treatment with alkali to remove free fatty acids ii) Treatment with steam to remove the odor (Deodorization) iii) Bleaching to remove the coloring matter

22. Characterization of Fat / Oils 1) Saponification number Saponification number of fats / oils is defined as the number of milligrams of alkali (like KOH) required to saponify one gram of fat/oil completely.  Significance: Saponification number is an indication of molecular weight of fat/oil. Saponification number is inversely proportional to the average molecular weight of fat/oil. Higher the saponification number, lower the molecular weight of fat /oil

23. Characterization of Fat / Oils 2) Iodine number lodine Number of fat/oil is defined as the number of grams of Iodine taken up by 100 grams of fat/oil. Signifance lodine number is an index of degree of unsaturation of fats and is directly proportional to the content of unsaturated fatty acids. Higher the Iodine number of fat/oil, higher the degree of unsaturation . Example: iodine number of coconut oil = 6 to 10; Sunflower oil = 124 to 136 . So this indicates Sunflower oil has higher degree of unsaturation

24. Functions of fat / lipids   Biological role of fats in the body Provision of energy : Fats are the concentrated form of energy. But fats are not the body's preferred fuel. Storage of energy : Stored fat in adipose tissues are the largest and efficient energy reserve than glycogen. Glycogen storage accompanies water, so it takes more space than fats which does not accompany water. Glycogen storage capacity is limited, but fat storage capacity is virtually unlimited. Glycogen stores last for only half a day, but fat reserves can last up to 2 months. Heat insulators : The fat stored subcutaneously serves as an insulator against heat loss to the environment. Fats also act as heat insulator against the cold. Shock absorbers : The subcutaneous fat deposits also insulate against mechanical trauma (act as shock absorbers), Fats deposits around the internal organs insulate and cushion them and protect them from mechanical injury.

25. Functions of fat / lipids Dietary role of different lipids Role of fats / oils in diet: Source of energy : Dietary fats provide energy. They contribute up to 20 to 30% of daily energy requirement Taste : Oils / Fats increase the taste and palatability of the food. They absorb flavors and aromas of ingradients to improve overall taste. Satiety : Fats increase the satiety value of the food because of their slow digestibility and increase in emptying time of stomach. Smooth mouth feel : Fats / oils provide creamy and smooth mouth feel. Dietary fats are the only sources of essential fatty acids : Absolute requirement of fats in the diet is not for energy, but for the provision of essential fatty acids. Essential fatty acids are required for eicosanoids synthesis and are important for epidermal growth, reproduction and promoting normal growth in children and cell membrane formation Digestion and absorption of fat soluble vitamins ; Fats act as vehicles for the digestion and absorption of fat-soluble vitamins and thus they promote the digestion and absorption of fat-soluble vitamins.

26. Functions of fat / lipids 2) Functions of other dietary lipids 5% of dietary lipids is made up of phospholipids and cholesterol Phospholipids: Phospholipids are not essential in diet as they are synthesized in the body. Phospholipids also provide almost 9 Kcal /gram of energy, like fats. Phospholipids are required for the formation of cell membranes, lipoproteins(transport form of lipids), blood clotting etc. Dietary sources: Phospholipids occur naturally in almost all foods; excellent sources are eggs, wheat germ and peanuts.

27. Functions of fat / lipids B. Cholesterol : • Cholesterol also forms a part of a balanced diet. • Cholesterol is not an essential nutrient as it can be synthesized in the body, A human being requires around 800 milligram of cholesterol per day. Out of this, about 300 mg generally provided by diet and rest can be synthésized in the body • Cholesterol does not provide energy. But cholesterol is required for synthesis of bile salts, vitamin D and variety of steroid hormones. .They are also important constituents of cell membranes. Dietary sources of cholesterol: Present in all animal foods, particularly rich in eggs.

28.  Calorific value of lipids (fats) The calorific value of fats is 9 Kcal/g (i.e. when one gram of fats is oxidized in the body, 9 Kcal of energy is liberated) Daily requirement (RDA) of lipids (fat ) It is recommended that lipids (mainly fats) provide about 20 % of the total daily energy requirement of the body. RDA for lipids for adults is about 0.8 gram/kg body weight/ day (About 40 - 50 grams for a 60 kg person). A minimum requirement of 25-30 grams of lipids is essential to meet the requirement of essential fatty acids and utilization fat- soluble vitamin Cholesterol also forms a part of a balanced diet. Diet should contain less than 300 mg of cholesterol. Phospholipids are not essential in diet as they are synthesized in the body.

29. Digestion, Absorption, Storage and metabolism of Lipids : Digestion of lipids More than 90% of the dietary lipids are fats and oil lipids are insoluble in water and lipid digesting enzymes are in water medium. This problem is overcome by emulsification of fats by bile salts in the intestine Very little digestion takes place in mouth and hence lingual lipase cannot act on them

30. A . Digestion of triacylglycerols (fat ) Digestion in the Stomach: Lingual and gastric lipases initiate lipid digestion by hydrolyzing triacylglycerols to form mainly 1, 2 diacylglycerols and free fatty acids  retention time of 2-4 hours in stomach, up to 30 % of fats can be digested in stomach. Peristaltic contractions of stomach emulsify lipids for some extent

31. Digestion of triacylglycerols (fat ) ii) Digestion in the Intestine: Pancreatic lipase enzyme hydrolyses triglycerides in the intestine the alkaline content of the pancreatic juice and biliary secretion neutralizes food & changes the pH and helps the action of pancreatic lipase. Bile also contains bile salts, which emulsify fats in the intestine

32. Digestion of triacylglycerols (fat Action of pancreatic lipase  pancreatic lipase hydrolyses triglycerides in the intestine. Colipase , a protein secreted by pancreas, acts ads cofactor for pancreatic lipase lipase Triacylglycerol 1,2 diacylglycerol + fatty acids colipase lipase colipase 2 monoacylglycerol + fatty acids isomerase 1 monoacylglycerol lipase colipase glycerol + fatty acids

33. B) Digestion of Cholesterol ester and Phospholipids Pancreatic secretion contains cholesterol esterase and phospholipase i ) Cholesterol esterase hydrolyzes cholesterol ester to cholesterol and fatty acid. ii) Phospholipase A, hydrolyzes phospholipids to lysophospholipid & fatty acid.

34.   Absorption of lipids : The water-soluble products of lipid digestion like glycerol as well as small and medium chain fatty acids are directly absorbed from the intestinal lumen in to the portal vein and taken to the liver and immediately utilized for energy The water-insoluble products like 2-monoacylglycerols, long chain fatty acids & cholesterol, phospholipids and lysophospholipids are Incorporated into bile salt micelles and absorbed into the intestinal cells .

35. Metabolism of lipids Lipolysis : Fatty acids are rich sources of energy. Triacylglycerols are the storage form of fatty acids, which are stored in adipose tissues. During the conditions of restricted diet (like starvation and diabetes mellitus), the stored triglycerides are broken down to glycerol and fatty acids by lipases. This process is called lipolysis . Fatty acid utilization Fatty acids released from adipose tissue are transported to tissues such as skeletal tissue, heart muscle, renal cortex, which utilize fatty acids as a source of energy by beta oxidation.

36. Lipogenesis and storage of fat : When excess of glucose are consumed in the diet, the surplus energy is first converted to glycogen and then to fatty acids. Fatty acids are then stored in the form of triacylglycerols in adipose tissues. Ketone bodies Liver produces ketone bodies (by ketogenesis ), which are utilized by extrahepatic tissues (by Ketolysis ). In starvation and diabetes, liver produces excess of ketone bodies, which finally lead to ketosis.

37. Cholesterol : Body requires around 1000mg (1g) of cholesterol per day. About 500 mg of cholesterol is synthesized in a day and other 500mg is provided by diet . Lipoproteins (Transport of lipids): Lipoproteins are the combination of lipids and proteins. There are four lipoproteins; Chylomicrons , VLDL (Very low density lipoprotein), LDL (Low density lipoprotein), HDL (High density lipoproteins). These contains variable amount of triglycerides,“cholesterol , cholesterol ester, phospholipids and fatty acids Functions of lipoproteins: Lipoproteins are the transport form of lipids. 1. Chylomicrons : Chylomicrons transport exogenous triglycerides from intestine to peripheral tissues like adipose tissue and skeletal muscle. 2. VLDL: VLDL transports endogenous triglycerides from liver to extrahepatic tissue like heart, adipose tissue, muscle, blood vessels etc. 3. LDL: LDL transports cholesterol from liver to extrahepatic tissues . 4. HDL: HDL transports cholesterol & cholesterol esters from extrahepatic tissue to liver.

38. deficiencies and overconsumption Deficiencies Deficiency of dietary lipids is very rare because they are widely distributed in foods. Deficiency of essential fatty acids and fat soluble vitamins  Risk includes infants consuming low fat diet include anorexic nervosa, patients receiving lipid-free parenteral nutrition for long periods with malabsorption syndrome.

39. deficiencies and overconsumption Overconsumption Over consumption of fats is associated with increased risk of certain chronic diseases, like, obesity, heart diseases, certain types of cancers etc.  Obesity : Obesity results from a chronic imbalance between energy intake and energy expenditure.  reasons are; Fat is more concentrated form of energy than carbohydrates and proteins. Obesity can also lead to type II diabetes mellitus and heart diseases. Body has the capacity to increase the utilization (oxidation) of carbohydrate and protein whenever their intake is high. But, body can not do so during high fat intak

40. ii)Coronary heart disease : Development of atherosclerosis and coronary heart diseases, Dietary cholesterol increases total and LDL-cholesterol Poly unsaturated fatty acids lower the levels of total and LDL-cholesterol and hence beneficial effect on CHD. iii) Cancer  High fat diet increase the risk of colon cancer and breastcancer . They may promote, not cause cancers .