Process of Metabolism

CHAPTER 5 PROCESS OF METABOLISM Objectives At the end of this chapter, the students should be able to: 1. differentiate catabolism from anabolism; and 2. determine the relationship between nutrition, metabolism, and energy. METABOLISM Metabolism is the chemica...

CHAPTER 5 PROCESS OF METABOLISM Objectives At the end of this chapter, the students should be able to: 1. differentiate catabolism from anabolism; and 2. determine the relationship between nutrition, metabolism, and energy. METABOLISM Metabolism is the chemical reaction involved in maintaining the living state of cells and organisms. Metabolism is divided into two categories: Catabolism - the breakdown of molecules to obtain energy Anabolism - the synthesis of all compounds needed by the cells Metabolism is linked to nutrition and the availability of nutrients. Bioenergetics describes the biochemical or metabolic pathways by which the cell ultimately obtains energy. One of the vital components of metabolism is energy formation. Nutrition, Metabolism, and Energy Nutrition is the key to metabolism. The pathways of metabolism rely upon the nutrients that they break down in order to produce energy. This energy in turn is required by the body to produce new proteins, nucleic acids (DNA, RNA), among other nutrients. Nutrients in relation to metabolism include bodily requirement for various substances, individual functions of the body, amount needed, and the level below which poor health results, among others. Essential nutrients supply energy (calories) and provide the necessary chemicals which the body itself cannot produce. Food provides a variety of substances that are essential for the building, upkeep, and repair of body tissues, and for the efficient functioning of the body. The diet needs important nutrients like carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, and around 20 other inorganic elements. The major elements are provided by carbohydrates, lipids, and protein. In addition, vitamins, minerals, and water are essential. Carbohydrates in Metabolism There are three forms of carbohydrates in food: starch, sugar, and cellulose (fiber). Starches and sugars are the major sources of energy for humans.Fibers provide bulk in diet. Body tissues rely on glucose for all activities. Carbohydrates and sugars produce glucose by digestion or metabolism. The overall reaction for the burning of glucose is written as: C6H12O6 + 6 O2 → 6 CO2, + 6 H2O + energy Most people consume half of their diet from carbohydrates such as dairy, grains, and starchy vegetables. Proteins in Metabolism Proteins are the main tissue builders of the body. Proteins aid in cell structure functions and hemoglobin formation to carry oxygen and enzymes in the execution of vital reactions and numerous other functions of the body. Proteins are also very important in supplying nitrogen for DNA and RNA genetic material and energy production. Proteins are needed for nutrition because they contain amino acids. Among the 20 or more amino acids, the human body is unable to manufacture 8 which are called essential amino acids. These include: 1. lysine 2. tryptophan 3. methionine 4. leucine 5. isoleucine 6. phenylalanine 7. valine 8. threonine Foods with high biologic value are eggs, milk, soybeans, meats, vegetables, and grains. Fat in Metabolism Fats are concentrated sources of energy. They create twice as much energy as either carbohydrates or protein on a weight basis. The following are the functions of fats: 1. to help form the cellular structure 2. to form a protective cushion and insulation around vital organs 3. to help absorb fat soluble vitamins 4. to provide a reserve storage for energy Essential fatty acids are unsaturated fatty acids that include linoleic, linolinic, and arachidonic acids. These are needed to be taken as part of one's diet. Saturated fats, along with cholesterol, have been implicated in arteriosclerosis and heart disease. Minerals and Vitamins in Metabolism The minerals in foods do not contribute directly to energy needs but are significant a body regulators and play a role in the metabolic pathways of the body. More than so elements are found in the human body. About 25 elements are found to be essential, since a deficit produces specific deficiency symptoms. Important minerals include: 1. Calcium 2. Phosphorus 3. Iron 4. Sodium 5. Potassium 6. Chloride Ions 7. Copper 8. Cobalt 9. Manganese 10. Zinc 11. Magnesium 12. Fluorine 13. lodine Vitamins are important organic compounds that the human body cannot synthesize by itself and must be present in the diet. Vitamins important in metabolism include: 1. Vitamin A 2. B2 (riboflavin) 3. Niacin or nicotinic acid 4. Pantothenic Acid METABOLIC PATHWAYS The chemical reactions of metabolism are structured into metabolic pathways. These allow the basic chemicals from nutrition to be changed through a series of steps into another chemical, by a sequence of enzymes. Enzymes are vital to metabolism because they allow organisms to drive desirable reactions that require energy. These reactions are also coupled with those that release energy. As enzymes act as catalysts they permit these reactions to proceed efficiently. Enzymes also allow the regulation of metabolic pathways in response to changes in the cell's environment or signals from other cells. CHAPTER 6 PHYSIOLOGIC VALUE OF FOOD Objectives At the end of the chapter, the students should be able to: 1. calculate the physiologic value of food; and 2. compute the desirable body weight and energy needs of an adult. FOOD Food refers to the solid and liquid materials taken into the digestive tract that are utilized to maintain and build body tissues, regulate body processes, and supply heat, thereby sustaining life. Food is composed of various compounds, both organic and inorganic, so that any food is either a chemical compound or a mixture of chemical compounds. These compounds and elements can be grouped as either organic and inorganic. Organic compounds are proteins, lipids, carbohydrates, and vitamins. Inorganic elements are water and minerals. The three major nutrients-carbohydrates, proteins, and fats-stand quite apart from the other requirements of the body such as vitamins and minerals since the former are needed in comparatively larger quantities. Vitamins and minerals act as catalysts which prompt the three major nutrients to interact. METABOLISM The word metabolism is derived from the Greek word metabolismos which means to change or alter. Metabolism is the chemical process of transforming food into complex tissue elements and of transforming complex body substances into simple ones, along with the production of heat and energy. It is the totality of the chemical processes in the body by which substances are changed into other substances to sustain life, thus it is the dynamic concept of change underlying all life. Energy is the force or power that enables the body to do its work. In nutrition, however, energy pertains to the chemical energy locked in foodstuffs brought about by metabolism. ENERGY FROM FOOD The Calorie The unit of energy commonly used in human nutrition is the kilogram calorie (kcal) or simply calorie. It is the unit of measurement for the energy that the body gets from food. 1,000 small calories = 1 kilocalorie or calorie Calories are not eaten. They are by-products of carbohydrates, proteins, and fats that are oxidized in the body. One kilocalorie is the amount of heat energy required to raise the temperature of 1 kilogram of water by 1°C. 1. Fuel factor of carbohydrate = 4 calories per gram 2. Fuel factor of fat - 9 calories per gram 3. Fuel factor of protein = 4 calories per gram The total calorie content (total energy) available from food can. be measured by a device called a bomb calorimeter. The Joule The joule is the measure of energy in the metric system. 1 calorie (kilocalorie) = 4.184 joule (kilojoules) Example: 1 cup of milk = 170 kcal 170 kcal x 4.184 kjoules = 711.28 kjoules Calculation of Food Value The energy value of one tablespoon of sugar (15 grams) is approximately 60 calories (15 × 4). Most foods, however, are complex and contain proteins, fats, and carbohydrates. For example, one cup of milk contains approximately: 12 gms carbohydrates × 4 cal/gm = 48 kcal 8 gms proteins x 4 cal/ gm = 32 kcal 10 gms fats × 9 cal/gm = 90 kcal Total = 170 kcal From this information, the percentage of each nutrient can be calculated. To calculate the percentage of kcalories from fat, for example, divide the 90 fat kcal by the total 170 kcal. 90 fat kcal / 170 kcal = 0.529 or 0.53 0.53 = 53% Table 31 Energy Allowances for Adults 22 Years of Age Body Weight Women Men kg kcal kjoules kcal kjoules 40 1,550 6,500 45 1,700 7,100  50 1,800 7,500 2,200 9,200 55 1,950 8,200 2,350 9,800 60 2,000 8,400 2,500 10,500 65 2,050 8,600 2,650 11,100 70 2,200 9,200 2,800 11,700 75 2,300 9,600 2,950 12,300 80 3,050 12,800 85 3,200 13,400 90 3,350 14,000 COMPONENTS OF ENERGY EXPENDITURE Basal Metabolism Basal metabolism, also known as the required energy expenditure (REE), is the measure of energy needed by the body at rest for all its internal chemical activities which is approximately 1 calorie per kilogram of body weight per hour for an adult. It is the minimum amount of energy needed by the body at rest in the fasting state. It also indicates the amount of energy needed to suction the life processes: respiration, cellular metabolism, circulation, glandular activity, and the maintenance of body temperature. It accounts for more than one-half of calorie requirements for most people. The basal metabolic rate (BMR) is the rate of basal metabolism in a given person at a given time and situation. It constitutes one-half of the calorie requirements of an individual Conditions Necessary for BMR Test To ensure accuracy: 1. The subject must be in fasting or post-absorptive state, at least 1 hour after the meal. (The test is usually taken in the morning.) 2. The subject must be awake, lying quietly, and free from physical fatigue, nervousness, or tension as this causes an increase in heat production. 3. The environmental temperature should be between 20 °C - 25 °C so that the subject can maintain his/her body temperature. Values obtained in this test which are within the plus or minus 10% are still considered normal. Calculation of BMR 1. A simple method for the calculation of the BMR is to use the rule of thumb 1 kcal per kg per hour for adult male and 0.9 kcal per kg per hour for adult female. Thus, an individual whose ideal body weight (IBW) is 50 kg has a basal metabolic energy need of 1,200 kcal per day (50 x 1 kcal x 24 hrs). This value, however, may not be applicable for obese or lean individuals. Example: Male, 75 kg = 1 kcal × 75 × 24 = 1,800 kcal Female, 65 kg = 0.9 kcal × 65 × 24  = 1,404 kcal 2. Another method is the Harris-Benedict formula, developed in 1909, which uses information on weight, height, age, and sex. Example: Males REE = 66 + [13.7 x wt(kg)] + [5 x ht(cm)] - [6.8 x age (yr)] Females REE = 655 + [9.6 x wt(kg)] + [18 x ht(cm)] - [4.7 x age (r)] 3. One more method used in obtaining the metabolic or fat-free body size is called the biologic body weight raised to the ¾ power. The metabolic body size for the different body weights is given in Table 32. Once the metabolic body size is known based on weight in kilograms, the figure is multiplied by 70, a value which applies to all animals. A 50-kg man's REE = 18.8 × 70 = 1,326 kcal 4. The last method is developed by WHO/FAO/UNU in 1985. It uses the following equation: 1.6 x wt (kg) + 879 = REE Thus, a 50-kg man has a REE of 1,459 kcal. Table 32 Body Weights in Kilogram and Metabolic Body Size (kg)¾ Kilograms Metabolic Body Size (kg)¾ 5 3.3 10 5.6 15 7.6 20 9.5 25 12.1 30 12.8 35 14.4 40 15.9 45 17.4 50 18.8 65 21.6 70 24.2 80 26.7 90 29.2  100 31.6 Factors that Affect the Basal Metabolic Rate (BMR) 1. Surface area - The greater the body surface area or skin area, the greater the amount of heat loss, and, in turn, the greater the necessary heat produced by the body, Muscle issue requires more oxygen than adipose tissue. 2. Sex - Women, in general, have a metabolism of about 5% to 10% less than that of men even when they are of the same weight and height. Women have a little more fat and less muscular development than men. 3. Age - The metabolic rate is highest during the periods of rapid growth, chiefly during the first and second years, and reaches a lesser peak through the ages of puberty and adolescence in both sexes. The BMR declines slowly with increasing age to lower muscle tone from lessened activity. Table 33 Adjustment of Kcalorie Allowances for Adult Individuals of Various Body Weights And Ages Ideal Body Weight Kcalorie Allowance kg lb 22 years 45 years 65 years Men 50 55 60 65 70 75 80 85 90 95 100 Women 40 45 50 55 58  60 65 70 4. Body composition - A large proportion of inactive adipose tissue lowers the BMR. Athletes with great muscular development show about 5% increase in basal metabolism over non-athletic individuals. 5. State of nutrition - A decrease in the mass of active tissue such as in the case of undernourishment or starvation causes a lowered metabolism often as much as 50% below normal. 6. Sleep - During sleep, the metabolic rate falls approximately 10% to 15% below that of waking levels. This decreased rate is due to muscular relaxation and decreased activity of the sympathetic nervous system. 7. Endocrine glands - The endocrine glands, which secrete hormones into the blood stream, are the principal regulators of the metabolic rate. The male sex hormones increase the BMR about 10% to 15% and the female sex hormones a little less. 8. Fever - It increases the BMR about 7% for each degree rise in the body temperature above 98.6 °F. Computation of DBW (Desirable Body Weight) 1. Ador Dionisio's Method Height - For every 5 feet, allow 100 lbs for female and 110 lbs for male. Then multiply the additional inches by 2. Age - Multiply any age between 25 and 50 by 2 then divide by 5. Example: Male, 45 years old, 5'4" tall Height = 5 feet = 110 lbs 4 inches x 2 = 8 lbs 118 lbs Age = (45 years)2 = 18 lbs 5 DBW = 118 lbs + 18 lbs = 136 lbs 2. Tannhauser's Method Measure height in cm and deduct 100. From the difference, take off its 10%. Example: Male, 45 years old, 5'4" tall Height = 5'4" = 162.56 cm 162.56 - 100 = 62.56 cm 10% of 62.56 cm = 6.256 62.56 - 6.256 = DBW (kg)  DBW (kg) = 56.7 kg or 126 lbs Physical Activity Calorie requirements depend on the type and amount of exercise. The more vigorous the physical work, the greater the calorie cost. The kind of physical activity and the amount of time spent determine the amount of energy the body uses. Table 34 Calorie Expenditure for Various Types of Activities Types of Activities Calories Sedentary Activities 80-100 reading, writing, eating, watching TV, office work, sitting at work Light Activities 110-160 cooking, washing dishes, ironing, welding, standing at work, rapid typing Moderate Activities 170-240 mopping, scrubbing, sweeping, gardening, carpentry, walking fast, standing at work with moderate arm movement, sitting at work with vigorous arm movement Heavy Activities 250-350 heavy scrubbing, hand washing, walking fast, bowling, golfing, heavy gardening Specific Dynamic Action of Food Carbohydrate or fat increases the heat production of about 5% of the total calories consumed. It is the energy required to digest, transport, and utilize food. Estimation of Daily Energy Requirement of an Adult The daily energy requirement of an adult is commonly estimated by adding together the requirements for basal metabolism, physical or muscular activity, and the specific dynamic action (SDA) of food: 1. Determine the DBW in kg of the individual. 2. Determine the basal needs: Male - 1.0 kcalorie/kilo of DBW/hr × 24 Female = 0.9 kcalorie/kilo of DBW/hr × 24 3. Subtract 0.1 kcalorie/kilo of DBW/hours of sleep. 4. Add the activity increment. 5. Add the SDA (10% of basal needs + activity increment). 6. Sum equals the approximate daily calorie requirement.  Table 35 Activity increment Activity kcalorie per day Men Women Sedentary or light work 225 225 Moderate work 750 500 Heavy work 1,500 1,000 Very heavy work 2,500 Estimation of Total Energy Need The total energy need of an individual is the composite of energy necessary to replace basal metabolic needs, energy expenditure for physical activities, thermogenic effect of food, and other factors. The total energy need of an adult may be determined using one of the methods on the following pages. 1. The most practical and rapid method of estimating energy need is based on desirable body weight (DBW) according to occupation. This method is often used in clinics and hospitals. Table 36 DBW According to Occupation Occupation or Activity Female Male kcal/lb kcal/kg kcal/lb kcal/kg Bed patient 12 25 14 30 Light work 14 30 16 35 Moderate work 16 35 18 40 Heavy work 18 40 20 44 Example: 50 kg man x 40 (moderately active) = 2,000 kcal/ day 2. The second method of estimating the energy need is the factorial method. It uses the following equation: Basal energy (a) + physical activity (b) + thermogenic effect of food (c) = total energy need a. Calculate the basal metabolic rate using any of the four methods discussed earlier. b. Determine the energy need for physical activity (PA) by using the short method (Table 34). c. Add the basal energy cost and activity cost. a. Calculate the thermogenic effect of food. For a mixed diet adequate in protein, add 10% of the subtotal. For the average Filipino diet, use 6%. e. Add the basal energy, physical activity, and thermogenic effect of food. Example: a. Basal metabolic rate using the Harris & Benedict formula REE = 66.5 + [13 × 50 kg] + [5.0 × 157 cm] - [6.8 × 35 (age)] = 66.5 + 685 + 785 - 238 = 299 kcal = basal metabolic needs b. Energy need from PA = total PA kcal x 50 (wt in kg) = 17.24 kcal × 50 kg = 862 kcal for PA c. Basal energy cost and activity cost = 1,299 kcal + 862 kcal = 2,161 kcal d. Thermogenic effect of food = basal energy cost + activity cost × 6% = (1,299 kcal + 862 kcal) (0.06) = 2,161 × 0.06 = 130 e. Basal energy cost, activity cost, and thermogenic effect = 1,299 kcal + 862 kcal + 130 kcal = 2,291 kcal Table 37 Approximate Increase Above Basal Need for Selected Activities Activity Category Percentage Above Basal Sleeping, reclining 10/% Very Light 30% sitting and standing, painting, driving, laboratory work, typing, playing musical instruments, sewing, ironing Light 50% walking on level 2.5-3 mph, tailoring, pressing, garbage work, electrical trades, carpentry work, washing clothes, golfing, sailing, playing table tennis, playing volleyball Moderate 75% walking on 3.5-4 mph, plastering, weeding and hoeing, loading and stacking bales, scrubbing floors, shopping with heavy load, cycling, skiing, playing tennis, dancing Heavy 100% walking with lead uphill, tree-felling, work with  pick and shovel, playing basketball, swimming, climbing, playing football 3. The daily energy need can also be determined by referring to the recommended dietary allowances for Filipinos (see Table 38), Table 38 Recommended Daily Energy Intake for Adults Age Men Women 20-31 2,580 1,920 40-49 2,450 1,820 50-59 2,320 1,730 60-69 2,060 1,540 70-79 1,810 1,340 4. The fourth method is recommended by FAO/WHO/UNU (1985). To get the energy need, multiply REE by the type of activity. Table 39 Energy based on Type of Activity Types of Activity Men Women Very Light 1.3 1.3 Light 1.6 1.5 Moderate 1.7 1.6 Heavy 2.1 1.9 Very Heavy 2.4 2.2 Example: Basal metabolic needs of a 50-kg man is 1,459 kcal * 1.7 (moderate) = 2,480 kcal Energy Balance The amount of energy taken in by an individual should be equal to the amount of energy expended during the day. If this is so, then the individual is said to be in energy balance and, thus, attains a desirable body weight. A desirable or ideal body weight is still debatable since body weight is made up of fats, muscles, organs, bones, and fluid. Two individuals having the same height and age may not necessarily have the same weight because of the aforementioned components. In the absence of tables, any of the two methods shown here may be used. 1. Tannhauser's Method  Height in centimeter = 157cm (factor) = 100 = 57 kg (10% of answer obtained to adjust weight to suit the Filipino standard) = 5.7 = 51.3 or 51 kg 2. For 5 feet, allow 100-105 Ibs (females); 105-110 Ibs (males). For each additional inch, add 5 lbs. 5'2" = 105 +10 = 115 lbs The values above apply to adults with small frame. Add 5 lbs for medium frame and 10 lbs for large frame. CHAPTER 7 WATER AND ELECTROLYTE BALANCE Objectives At the end of the chapter, the students should be able to: 1. describe body fluid composition; 2. explain the mechanisms controlling fluid and electrolyte movement; and 3. identify the major anions and cations in the fluid compartments of the body. WATER Water constitutes about 60% to 70% of the total body weight so that a deprivation of water by as much as 10% will already result in illness and a 20% loss of body water may cause death. It is next to oxygen in importance for the maintenance of life. Water found in a normal adult human body totals 45 liters. Two thirds of this (30 liters) is found inside or within the cell while one third (15 liters) is outside the cell. Functions 1. Water is the universal solvent. 2. Many chemical reactions require water. It serves as a catalyst in many biological reactions especially those that involve digestion, absorption, and circulation. 3. It is a vital component of tissues, muscles, glycogen, and others and is essential for growth. 4. Water acts as a lubricant of the joints and the viscera in the abdominal cavity. 5. It is also a regulator of body temperature through its ability to conduct heat. Water Intake The amount of water needed by the body may be met by a direct intake of water, water ingested as such, or from water bound with foods, and from metabolic water, which is a result of oxidation of foodstuffs in the body. Water produced as an end product of metabolism amounts to approximately 14 g/100 cal. For example, 100 g of fats, carbohydrates, and proteins when oxidized will yield 107 mL, 60 mL, and 41 mL of water, respectively. Water Output Water leaves the body via several channels such as through the skin as an insensible perspiration; through the lungs as water vapor in the expired air; through the gastrointestinal tract as feces; and through the kidneys as urine. Water may also be lost together with the electrolytes through tears; stomach suction; breathing; vomiting; bleeding; perspiration; drainage from burns; and discharge from ulcer, skin diseases, and injured or burned areas. Table 40 Fluid Requirement Based on Caloric Expenditure Using the Holliday-Segar Method Weight Daily Requirement 3-10 100 mL/kg 10-20 1000 mL + 50mL/kg for each kg in excess of 10 > 20 1500 mL + 20mL/kg for each kg in excess of 20 Source: Holliday & Segar, 1957 Note: This method is not suitable for neonates < 14 days old or for conditions associated with abnormal losses. ABNORMALITIES OF WATER BALANCE Overhydration or Water Intoxication When large amounts of water are lost in the body usually caused by high environmental temperature, sodium is also lost. This phenomenon causes the brain to signal a need for increased water. If the water intake is increased without the corresponding increase in the intake of sodium, water intoxication results. Workers exposed to high environmental temperatures and travellers to tropical countries not accustomed to heat may become victims of this condition and experience muscle cramps, weakness, or drop in blood pressure. This is relieved by providing sodium in very small amounts with the intake of solids. This may also arise if too much fluid is given intravenously. If the intake of water exceeds the maximum rate of urine flow, the cells and tissues become water-logged and diluted. This may cause anorexia and vomiting, and if it occurs in the brain, it may result in convulsion, coma, and éven death. Dehydration This condition becomes serious if the loss is about 10% of the total body water and fatal if the loss is from 20% to 22%. It is especially critical in babies. Electrolytes are also lost with the water in this condition, and the skin becomes loose and inelastic. Table 41 Average Daily Intake and Output of Water Intake mL/day output mL/day Oral fluids 1,100 - 1,400 sensible Solid foods 800 - 1,00 urine 1,200 - 1,500 Metabolic water 300 intestinal 100 - 200 (oxidation of food insensible lungs (water vapor) 400 skin (sweat) 500 - 600 TOTAL 2,200 - 2,700 2,200 - 2,700 (approx. 2500 (approx. 2,500 mL/day) mL/day) Table 42 Methods of estimation of Daily Food Requirements Method of Estimation Fluid Requirements, mL/kg Body Weight mL/kg Adults, y 40 Young active, 15-30 35 Average, 25-55 30 Older, 55-65 25  Elderly, >65 Children, kg 100 1-10 Additional 50 mL/kg in excess of 10 kg 11-20 Additional 20 mL/kg in excess of 20 kg 21 or more Additional 15 mL/kg in excess of 20 kg At age > 50 Energy Intake 1 mL/kcal for adults 1.5 mL/kcal for infants Nitrogen + Energy Intake 100 ml/g nitrogen intake + 1 mL/kcal Body Surface Area 1500 mL/mb Body surface area may be calculated based on the following formula: 5 = W0.425 x H0.725 x 71.84 or log x = (log W x 0.425) + (log H × 0.725) + 1.8564; where x = cm2 body surface area, W = kg body weight, and H = cm height Body surface often used for "average" adult is 1.73 m2 Sources: Zeman & Ney, 1996 FNRI-DOST RENI, 2002 Table 43 Normal Electrolyte Concentrations of the Extracellular and Intracellular Fluids (mEq/liter) Extracellular Fluids Intracellular Fluids (Plasma & interstitial) (mEq/liter) (mEq/liter) CATIONS (+): Sodium (Nat) 135 to 147 10 Potassium (K+) 3.5 to 5.5 150 Calcium (Ca++) 4.5 to 5.5 1 to 2 Magnesium (Mg++) 1.5 to 3.0 40 ANIONS (-): Chloride (CI) 98 to 106 4 Bicarbonate (HCO3-) 26 to 30 10 Phosphate (HPO4-) 2 to 5 140 Sulfate (SO4-) 2 to 5 10 Organic Acids (Lactic, pyruvic) (-) 3 to 6 40 Proteins (proteinate -) 15 to 19