Human Nutrition PDF

HUMAN NUTRITION  Nutrients are food constituents necessary to sustain normal functions of the body.  Nutrients provide: Energy Essential molecules That either cannot be synthesized by all tissue or their rate of synthesis is not sufficient to meet the needs for growth and maintenance....

HUMAN NUTRITION  Nutrients are food constituents necessary to sustain normal functions of the body.  Nutrients provide: Energy Essential molecules That either cannot be synthesized by all tissue or their rate of synthesis is not sufficient to meet the needs for growth and maintenance. DIET Recommended daily dietary allowances (RDA) is an estimate of nutrient amount to meet the basic needs in various conditions of health and diseases to provide an ample safety margin of life.  FACTORS AFFECTING RDA  Age : RDA increases from infancy to adulthood.  Infants need over 2 g protein/kg bw/day  Adults need 0.8 g protein/kg b.w./day  Sex: Daily allowance for men is 20% greater than those for women due to larger body mass for men.  Iron is an exception, because women must replace iron lost during menstruation.  In pregnancy and lactating women most nutrients are increased by 20-30% above normal RDA.  In illness and injury some RDA are increased.  Maintenance of optimal health and prevention of chronic disease may require certain nutrients in greater amounts than the RDA. Eg. Daily intake of 33 mg of Vitamin E which is more by 330% of RDA reduces the risk of “coronary artery disease”.  Energyis calculated from the heat released by total combustion of food in a calorimeter and is expressed in Kcal or Cal.  One calorie is the heat required to raise the temperature of 1 g of water by 1o C.  Energy content of major food stuffs:  Carbohydrate : 4 Kcal/g  Protein : 4 Kcal/g  Fat : 9 Kcal/g RECOMMENDED ENERGY INTAKE FOR MEN AND WOMEN SEX AGE (years) WEIGHT ENERGY (Kg) NEEDS (Kcal) Men 23--50 70 2900 Women 23--50 50 2200 Pregnant +300 Lactating +500 Sedentary adults (less activity) require 30 kcal/kg/day. Moderately active adults require 35 kcal/kg/day Very active adults require 40 kcal/kg/day  BODY MASS INDEX Body mass index = weight (in kg/ )/height2( in metre )  Body mass index (BMI) Category BMI range – kg/m2 Normal from 18.5 to 24.9 Overweight from 25 to 29.9 Obese from 30 to 34.9  MACRONUTRIENTS: Are those foods whose requirements are larger than that of other dietary nutrients. Eg. Carbohydrates, proteins and fats  MICRONUTRIENTS: Are those nutrients that are needed in lesser amounts, such as vitamins and minerals. ROLE OF DIFFERENT FOODS Adults should consume 45 to 65% of their total calories from carbohydrates 20 to 35% calories from fats 10 to 35 % calories from proteins. Carbohydrates provide energy and fiber Fats provide energy and essential fatty acids Proteins provide essential amino acids for protein synthesis.  Carbohydrates like glucose, fructose, sucrose, lactose, maltose, starch and glycogen forms the main source of energy.  Non-digestible carbohydrates like cellulose, lignin and pectin do not provide any energy but serve as dietary fiber which have several beneficial effects Effects of dietary fibre They absorb water to about 10 - 15 times that of its own weight and so increase bowel motility Reduces constipation Decreases absorption of dietary fat & cholesterol and help in decreasing blood cholesterol Delays gastric emptying Generates sensation of fullness They decrease the absorption of toxic compounds including certain carcinogens  Drawbacks of dietary fibre Dietary fiber can bind the trace elements like zinc and decreases its absorption. Excess fiber in the diet decreases absorption of fat soluble vitamins So supplementation of diet with excess fiber is not recommended Only moderate amounts of fiber to about 20 – 35 g/day which is obtained naturally form whole grain cereals, bread, vegetables and fruits is recommended. Importance of fats in the diet Fats help in absorption of fat soluble vitamins. They supply more amount of energy as compared to carbohydrates and proteins. Fats are required in the diet for their essential fatty acid content. Essential fatty acids are those which cannot be formed by the body and have to be taken in diet. Eg. Linoleic and Linolenic acid. Linoleic acid is the precursor of Arachidonic acid. Arachidonic acid becomes essential if linoleic acid is deficient in diet. Deficiency of essential fatty acids leads to scaly dermatitis, hair loss and poor wound healing. High consumption of fat causes atherosclerosis and coronary heart disease. Proteins are required in the diet for their essential amino acid content Essential amino acids are those that cannot be synthesized by the body and have to be taken in the diet. Methionine, Valine, Phenylalanine, Isoleucine, Threonine, Leucine, Lysine, Tryptophan, Arginine and Histidine (required during growth and repair) RECOMMENDED PROTEIN ALLOWANCES Infants ------ 2g/Kg body weight/day Adult ------0.8 g/Kg body weight/day Women (in pregnancy/lactation)------ require upto 30 g/day in addition to their basal requirement  BIOLOGICAL VALUE OF PROTEINS It is measured by its ability to provide essential amino acids. Proteins from animal sources (meat, poultry, fish and milk) have a high biologic value, because they have all essential amino acids. Proteins from plant sources (wheat, corn, rice and legumes) are deficient in may of the essential amino acids, so they have low biologic value than animal protiens. However combination of proteins from different plant sources can provide a good nutritional value Ex. Wheat (lysine deficient, methionine rich) + beans (methionine poor, lysine rich) or Cereal and milk.  NITROGEN BALANCE When the amount of nitrogen taken in the diet is equal to nitrogen excreted in urine, sweat and feces, then the person is said to be in nitrogen balance. (seen in healthy adults). If the nitrogen intake is more than excretion then it is called positive nitrogen balance. (seen in children, pregnancy and recovery from illness) If nitrogen loss is more than intake then it is called negative nitrogen balance. (during inadequate dietary protein, lack of essential amino acids, during physiologycal stress like trauma, burns, illness and surgery.) DISEASES DUE TO NUTRITIONAL FACTORS Consumption of saturated fats results in increased risk of cardiovascular disease Consumption of n-6 polyunsaturated fatty acids lowers plasma LDLs, but HDL which protect against coronary heart disease, are also lowered. Consumption of n-3 polyunsaturated fats reduce the risk of cardiovascular mortality. Kwashiorkor is caused by inadequate intake of protein(less intake than expenditure). Marasmus occurrence increases prior to age 1, whereas kwashiorkor occurrence increases after 18 months. It can be distinguished from kwashiorkor in that kwashiorkor is protein deficiency with adequate energy intake whereas marasmus is inadequate energy intake in all forms, including protein..  MARASMUS Marasmus is due to deficiency of dietary energy and protein Usually occurs in children younger than 1 year of age. Usually found in poor population suffering from food shortage.  Clinical Features: Diarrhea is frequent, child is smaller than normal with weight much lower than normal. MARASMUS  KWASHIORKOR It is due to quantitative and qualitative deficiency of protein. *Clinical Features : Edema, anorexia, diarrhea, growth retardation, big belly due to edema. Marasmus and Kwashiorkor are known as Protein calorie malnutrition