Energy notes 2024.pdf

ENERGY Energy is the ability to do work. The energy contained within the chemical constituents of food can be either trapped within the chemical constituents of the body or used to produce heat or allow the body to move. Combustion of food yields energy:...

ENERGY Energy is the ability to do work. The energy contained within the chemical constituents of food can be either trapped within the chemical constituents of the body or used to produce heat or allow the body to move. Combustion of food yields energy: O2 Carbohydrates and fats CO2 + H2O + Energy O2 Proteins CO2 + H2O + Energy + Urea Carbohydrates, fats and proteins in the food are called as energy yielding nutrients or proximate nutrients. UNITS All forms of energy are interconvertible. The energy value of food is expressed in kilocalories. A Kilocalorie of energy is defined in terms of the amount of heat energy to which it corresponds. One kilocalorie is defined as the amount of heat energy required to raise the temperature of 1kg of water by 1oC from 14.5oC to 15.5oC at normal atmosphere pressure. The unit of energy, which has been used in nutrition for a long time, is the kilocalorie. However, recently the International Union of Science and the International Union of Nutritional Science (IUNS) have adapted 'Joule' as the unit of energy in place of kcal. A joule is defined as energy required to move 1 kg mass by 1 metre by force of 1 newton acting on it. One newton is the force needed to accelerate 1kg mass by 1m per sec. The inter-conversion factors are: 1 kcal = 4.184kJ. DETERMINATIONOF ENERGY VALUE 1. Direct Calorimetry Much of our information about how much energy is in foods is obtained by direct calorimetry, or the direct measurement of heat. Direct calorimetry involves an instrument known as a bomb calorimeter, which is a highly insulated, compact, box like container, about 1 cubic foot in size. A dried sample of food is completely burned within the container, and the heat produced is absorbed by the water surrounding the chamber. By measuring the change in temperature of the known amount of water in the container, it is possible to calculate the number of kilocalories of heat produced by burning the sample. Because the bomb is well insulated, no heat is lost to the air. A single bomb calorimeter determination takes about 20 minutes. However, it must be preceded by the time-consuming processes of precise weighing and careful drying of the sample.  Bomb-Calorimeter 2. Indirect Calorimetry Indirect calorimetry is a much simpler, less costly method in which energy needs are determined by measuring oxygen consumption. For many years the Benedict Roth respiration apparatus was the standard machine used for this purpose. This apparatus is a closed-circuit system in which the subject receives oxygen only from a measured source of oxygen-rich air and exhales into a container in which the carbon dioxide and water are removed and the remaining oxygen and nitrogen are recirculated. HEAT OF COMBUSTION / GROSS ENERGY VALUE (GE) Energy determined in the bomb calorimeter from complete oxidation of food is called the heat of combustion or gross energy value. But not all this energy is available to the body because some losses occur through faces and urine. When losses are subtracted from gross energy value, it is called metabolizable energy (ME) GE- losses = ME PHYSIOLOGICAL FUEL VALUE The amount of energy actually available to the body from a given amount of nutrient is called physiological fuel value. In the bomb calorimeter, unlike in the human body, carbohydrates, fats and proteins are completely oxidised. In the human body the process of digestion does not proceed with 100 percent efficiency and so the entire amount of any ingested nutrient does not eventually become available to the body. The efficiency with which nutrient is digested must be taken into account. The coefficient of digestibility is used to express the proportion of an ingested nutrient that ultimately becomes available to the body cells. For carbohydrate, fat and for protein the coefficient of digestibility is 0.98, 0.95 and 0.92 respectively. Therefore, the heat of combustion values is higher than the physiological fuel values. In bomb calorimeters, the fibre present in vegetable foods is burnt and yields energy that is not utilised by human beings. There is no loss of energy in metabolism of carbohydrate and fat. But in the case of protein, a part of the energy is lost as urea due to incomplete oxidation. The physiological energy values of carbohydrate, fat and protein are 4, 9 and 4 kcal after making allowances for losses of food energy in digestion and metabolism. These values are known as Atwater Bryant factors or physiological fuel values Coefficient of Digestibility Once food has been taken in, the body is not 100% efficient in digesting (preparing food for absorption) or absorbing nutrients. We must therefore take into account how much of the nutrients consumed actually become available to the cells. The extent of digestion varies from one nutrient to another and is further influenced by the food in which a nutrient is found. To calculate the potential energy from carbohydrate, fat, and protein representative coefficients of digestibility are used to express the percentage of the nutrient that is ultimately available. For carbohydrate, fat, and protein, the coefficients of digestibility are0.98, 0.95, and 0.92, respectively, showing that they are 98%, 95%, and 92% digested. COMPONENTS OF ENERGY EXPENDITURE There are 3 components: 1. Basal metabolic rate 2. Physical activity 3. Thermic effect of food 1. BASAL METABOLIC RATE (BMR) It forms a major component of the total energy expenditure. The amount of energy required to carry on the involuntary work of the body is known as basal metabolic rate. It includes the functional activities of the various organs such as brain, heart, liver, kidney and lungs. The secretory activities of glands, peristaltic movement of gastro-intestinal tract, oxidation occurring in resting tissue, maintenance of muscle tone and body temperature. The basal metabolic rate is measured by indirect calorimetry under the following conditions: Post absorptive stage: 12-16 hrs after the meal usually performed in the morning. Reclining but awake: 11/2 hrs - 1 hr rest before the test is necessary if there has been any activity in the morning. Relaxed and free from emotional upsets or fear of the test itself. Normal body temperature. Comfortable room temperature and humidity of about 21oC - 24oC. image: Wikipedia FACTORS AFFECTING BASAL METABOLIC RATE There are many factors that determine basal metabolic rate of an individual. 1. Body Composition: All body tissues are metabolically active and being constantly maintained. Their components are degraded and re-synthesised with an accompanying requirement of energy. The kind of tissue that makes up the body has a direct influence on BMR. Adipose tissue is metabolically inert and muscle is highly metabolic, therefore more energy is expended. An athletic type of man with well- developed muscles will have 6% higher BMR than a non-athlete. 2. Gender: Women have more adipose tissue and less muscle tissue compared to the men of the same height and weight. Young adult male contains 14 percent of fat and young adult females contain 23-32 percent of fat. The BMR for women is 10-12 percent lower than those of men of the same age, height and weight females have lower BMR than males. In women there is premenstrual rise and postmenstrual fall in the basal metabolic rate. 3. Age: The BMR is at its highest during the first two years of life. It declines gradually throughout childhood and accelerates slightly in adolescence. Thereafter the decline continues throughout life, with an average of about 2 percent per decade after the age of 21 years. The rapid growth rate explains the high metabolic rate in early childhood. Whenever there is growth there is an increase in the BMR. In the later years muscle tone decreases and there is reduction in muscle mass and hence the BMR is low. 4. Body size and Surface area: About 80 percent of energy is from glucose and the fat, which is lost as heat, 15 percent of the heat loss being from the skin. The remaining heat loss occurs from the lungs and through excreta. Since the heat loss is proportional to the surface area. Basal metabolism is most closely related to the body surface area and less directly related to either weight or height of an individual. A tall thin person has greater surface area than an individual of the same weight who is short and fat. The former will have higher basal metabolism. 5. Sleep: During the sleeping hours the basal metabolism is about 10 percent lower than the waking state. It also depends on the amount of motion during sleep of an individual. 6. Body temperature: An elevation in the body temperature above 37oC or 98.6 of increase the basal metabolism by 13 percent for each degree Celsius, 7 percent for each degree of Fahrenheit. Increase in chemical reaction increases the temperature hence increase in BMR. Calorie requirement increases during fever. 7. Endocrine glands: The hormone thyroxine, containing iodine, is secreted by the thyroid gland and is a powerful stimulator of metabolism. In hypothyroidism BMR may be depressed as much as 30 percent, a result of under secretion of thyroxin. People with hypothyroidism have low total energy needs and so they gain weight easily. In hyperthyroidism basal metabolism is elevated to 50-70 percent above the normal level due to over secretion of thyroxin. The growth hormone that stimulates new tissue formation is responsible for enhanced metabolism that is observed in children, infants, and teenagers. An increased secretion of epinephrine during excitement or fear temporarily raises the metabolic rate. 8. Pregnancy: BMR increases by about 5 percent during the first and second trimesters. During the last trimester the BMR increased by 12 percent. This increase can be accounted for by the high rate of metabolism of foetus and placenta, the increased activity of maternal tissue and increase in weight of the mother. 9. State of nutrition: After prolonged calorie undernutrition the BMR may fall to at least 20-30 percent below normal. This reflects the body's adaptive efforts to conserve energy when there is a deficiency. BMR is affected by food consumption. Over feeding increases BMR by 5-10 percent while underfeeding reduces BMR. 10. Environment temperature: The lowest metabolic rate is observed at an environment temperature of 26o C. Higher metabolic rates are observed at temperatures both above and below this figure. A sudden increase in environmental temperature causes shivering and a temporary process of heat production with the result there is an increase in BMR. This adaptive response of the body to lowered environmental temperature is called "Cold Induced Thermogenesis". Temperature above the normal temperatures also leads to sweating which increases BMR. 11. Smoking: Research indicates that habitual smokers when they stop smoking tend to gain weight. This may be caused by the fact that the nicotine taken in increases BMR by 10 percent. 12. Genetic difference: BMR varies by up to +- 10% between individuals of the same age, sex, body weight and fat free mass and there is growing evidence that some of this variation is determined by genetic factors. 13. Psychological state: Psychological state may affect energy expenditure as acute anxiety is a potent stimulant of epinephrine secretion and this increases energy expenditure. 13. Pharmacological agents: Nicotine and caffeine increases energy expenditure by small but measurable amounts. Beta-blockers commonly used to treat hypertension may lead to a slight decrease in energy expenditure and hence a tendency to gain weight. 14. Disease process: This may increase metabolic rate like in fever, tumours and burns to the skin. Factors affecting basal metabolism _____________________________________________________________ 2. PHYSICAL ACTIVITY After BMR, physical activity constitutes the next major component of energy expenditure. Physical activity includes amount of work, intensity of work performed and the duration. According to work, there are 3 types of energy expenditure: 1. sedentary – walking, sitting, office workers, teachers, lawyers, doctors, drivers, shopkeepers 2. moderate - railway workers, postman, plumbers, bus conductors 3. 3.  heavy - miners, steel workers, farm labourers, construction workers 3. THERMIC EFFECT OF FOOD (TEF) / SPECIFIC DYNAMIC ACTION (SDA) The thermic effect of food refers to the stimulation in metabolism and therefore the production of heat that occurs from 1 to 3 hours after a meal as the result of the presence of food in the stomach and intestine and digested nutrients in the bloodstream. The increase in energy cost because of this thermogenesis amounts to about 10% of the total for basal metabolism and activity. The effect varies with the composition of the diet. Protein when eaten alone has been shown to increase the metabolic rate by 30%, whereas carbohydrates and fats produce much smaller increases – 5% on the basis of mixed diets usually eaten, SDA is 6% of total energy expenditure. *******************