بسم الله الرحمن الرحيم Community Medicine
Lecture-4-
Learning objectives
At the end of this lecture student would be able to : 1-Determine fats constituents . 2-Classify fatty acids . 3-Illustrate functions of dietary & body fats . 4-Outline health problems of fats . 5-Identify functions & properties of essential fatty acids . 6-Discuss cholesterol & types of lipoproteins . 7-Enumerate indications & contraindications of weight reduction .
Fats
Fats are solid at 20 deg.c, they are called oils if they are liquid at that temperature. Fats and oils are concentrated a main sources of energy They are classified as : 1- simple lipids e.g triglycerides 2- compound lipids e.g phospholipids 3- derived lipids e.g cholesterol The human body can synthesis triglycerides and cholesterol endogenously . Most of body fat (99%) in the adipose tissue in the form of triglycerides. In normal human subjects , adipose tissue constitutes between 10-15 % of body weightFats
Glycerol + one fatty acids Monoglyceride. Glycerol + 2 F.A. Diglyceride. Glycerol + 3 F.A. Triglyceride.Fats are compounds of glycerol with fatty acids. Fatty acids are either saturated or unsaturated. By hydrogenation ,unsaturated fatty acids are changed into saturated ones. Hydrogenation destroy the essential fatty acids.
Essential fatty acids can not be synthesized by human body.
Essential fatty acids
1- Essential fatty acids are those that cannot be synthesized by humans 2- They can be derived only from food 3- The most important essential fatty acids (EFA) is Hnoleic acid which serves as a basis for the production of other essential fatty acids (e.g linoleic and arachidonic acids ) 4- Not all polyunsaturated fatty acids are essential fatty acids
5- Essential fatty acids are essential for maintaining normal health, otherwise its absence will create specific health problems e.g. linoleic acid , linolenic acid,and arachidonic acid deficiency states or conditions.
Essential fatty acids functions and properties
1. Strengthening function for capillary and cell membrane ( increase its permeability). 2.Combine with cholesterol and enhance its transport. 3.Help in lowering serum cholesterol levels. 4.prolongation of blood clotting time and increase the fibrinolytic activity. 5.It help in prostaglandins formation and functions on platelets smooth muscles.Unsaturated fatty acids
They are present mainly in vegetable oil and play an important role in having a lowered serum cholesterol level. Unsaturated fatty acids further divided into :1- monounsaturated (MUFA) e.g oleic acid 2- polyunsaturated fatty acids (PUFA) e.g linoleic acid and a- linolenic acids مقطع مضاف Triglycerides are oily droplets circulate in blood shielded with water soluble proteins in the lipoprotein complexes.Occurrence of fats ( Sources of fatty acids ) In general fats could be either of plant origin or of animal origin.
In plants ,fats are formed from carbohydrates .The plant seeds when become ripen, starch content becomes less while fatty content increase .e.g. cotton seeds ,sun flower seed. Otherwise most vegetables and fruits contain a very little amount of fats. Plant origin fats are usually of unsaturated fatty acids.In animals, when much starchy food has been consumed fats are laid down in animal body .Some naturally formed fats contain vitamins such as vitamin A,D and E .Animal origin fats are usually of saturated fatty acids.
Fat requirements
In developed countries , dietary fats provides 30 – 40 % of total energy intake .The WHO Expert committee on prevention of coronary heart diseases has recommended only 20- 30 % of total dietary energy to be provided by fats .At least 50% of fat intake should consists of vegetable oils rich in essential fatty acids .Visible and invisible fats
Visible fats : Those are separated from their natural sources e.g: ghee ( butter ) from milk , cooking oils and oil- bearing seeds and nuts It is easy to estimate their intake in the daily diet Invisible fats : Those which are invisible to the naked eye and they present in almost every article of food e.g: cereals, pulses It is difficult to estimate their intakeFunctions of dietary fats 1.Source of energy Fats are essential nutrients that supply a high energy density. 1 gram 9 Cal. 20% of-- daily required energy is ideally derived from fats. 2.Supply of essential fatty acids specially linoleic acid. 3.Supply of fat soluble vitamins. 4.Food satisfaction feeling Fats has a slow gastric emptying thus it play a satisfactory role against rapid hunger.
Functions of body fats
1.Energy production The major function of fats in the body is energy supplement to all body tissues except central nervous system. 2.Thermal insulation for body The fatty layer beneath the skin (subcutaneous fat) preserve the overall body temperature. 3.Vital organs protection The adipose tissues which surround vital organs in the body display a protective role for these organs against trauma .e.g. kidney.The fatty layer which surround the nerve fibers provide electrical insulation and enhance the transmission of nerve impulses.
4.Nervous stimuli transmission
5.Tissue membranes structure Fats are vital constituents for tissues and cells membrane structure and help in the transport of nutrients and metabolites across membrane. 6.Cell metabolism The combination of protein with fats help in cell metabolism .Lipoproteins carry fats in blood to all cells.
Fatty acids and cholesterol are essential precursors for the synthesis of many materials that are needed by the body for maintaining metabolic functions and tissue integrity.
Health problems of fats A. Excess amounts of fat intake can lead to much adipose tissues deposition and thus overweight or obesity. B. Excess saturated fatty acids intake usually associated with a great risk to develop atherosclerosis
7.Precursor substances.
( fat and disease occurrence )
1- Obesity : A diet rich in fat can pose to human health by encouraging obesity In fatty people , adipose tissue may increase up to 30% 2- Phrenoderma : Deficiency of essential fatty acids in the diet is associated with rough and dry skin , a condition known as (Phrenoderma) or toad skin It is characterized by horny popular eruption on the posterior and lateral aspects of limbs and on the back and buttocks3- Coronary heart disease
High fat intake ( dietary fat representing 40% or over of the energy supply and containing a high proportion of saturated fats ) has been identified as a major risk factor for CHD 4- Cancer : There has been some evidence that diets high in fat increased the risk of colon cancer and breast cancer .Cholesterol
It is not a fatty material .It is a fat related substance. It traveled in blood stream attached to a long chain of fatty acids to form cholesterol esters. It is a vital substance in human metabolism. It is an important precursor for all steroid hormones. It is essential for bile acids formation. It is found naturally in all animal origin foods especially in egg yolk, liver and kidney. Other wise,it can not be found in plant origin foods. Its main health related problems lie in cases of high serum cholesterol levels which reveal a direct association with atherosclerosis and I.H.Dlipoproteins
They serve as a major vehicle for transport of fats in blood stream. As fats are insoluble ,thus it trapped by water soluble proteins for transport. Types of lipoproteins are:-
1.Chylmicrons It is the lowest density i.e. small amount of proteins and high amount of triglyceride Liver cells. 2.Regular density lipoproteins (VLDL) tissue cells (endogenous triglycerides) 3. Intermediate low density lipoproteins (ILDL) endogenous triglycerides to cells.
4.low density lipoproteins (LDL) Transfer cholesterol to peripheral tissues cells. 5.High density lipoproteins (HDL) Transfer free cholesterol to liver for catabolism and excretion.
Prostaglandin
It is a group of compounds , recognized as ( local hormones ) which play a major role in controlling many of the physiological functions of the body like A- vascular homeostasis B- kidney function C- acid secretion in stomach D- gastro- intestinal motility E- lung physiology F- reproductionIndications of weight reduction
Although weight reduction is desirable measure for all obese persons to get rid of the somatic and psychological difficulties ,the followings are serious indications:- 1.Respiratory difficulties Excessive deposition of adipose tissue increase the work load of respiratory movements for keeping sufficient oxygenation of whole body tissues.2.Hypertension Weight reduction can play an important role in the control of hypertension among obese persons.
3.Ischemic heart disease It is advisable to reduce weight during post coronary ischemia e.g. post angina or post infarction. 4.Endocrine and metabolic disturbances Uncontrolled diabetes, hirsutism and menstrual irregularities are more common among obese females. A better control of such disturbances can be obtained through weight reduction.
5.Reproduction difficulties Toxemia of pregnancy Infertility Serious reproductive difficulties can be eliminated through a proper weight reduction.
6.Gall stones and gall bladder diseases 7.Dermatological problems Skin rash, certain inflammatory skin conditions and varicose vein ulcers can be avoided through weight reduction. 8.Rheumatological problems. 9.Psychological indications.