ENERGY 1 Energy is defined as the ability to do work. Energy exists in several forms. The forms of energy important in nutrition are: 1. Chemical energy in food. 2. Light or solar energy for synthesis of vitamin D in the skin and for photosynthesis is plants. 3. Mechanical energy for movement of muscles. 4. Electrical energy for functioning of the brain and Nerve cells. 5. Heat energy, generally produced when energy is converted from one form to another. The energy from food is finally converted into heat energy. UNITS OF MEASUREMENT The energy present in food or the energy needed by the body is measured in units called joules or calories. The calorie in nutrition is the large calorie or kilocalorie. The kilocalorie is defined as the amount of heat required to raise the temperature of 1 kg (1000g) of water by 1 o C. This calorie is 1000 times bigger than the calorie used in physics. The international unit for energy is the joule (J) and it is the energy expended when 1 kilogram (kg) is moved 1 metre (m) by a force of 1 newton (N). Scientists and nutritionists are concerned with large amounts of energy, so they use the units kilocalorie, kilojoules (kj= 10 3 J), or megajoule (MJ=10 6 J) to express energy. 1 kilocalorie = 4.184 kilojoules 1 megajoule = 239 kilocalories ENERGY VALUE OF FOOD The energy content of various foods can be measured in two ways: a. by calorimetry or b. by proximate composition. a. Calorimetry The bomb calorimeter is based on the principle of calorimetry. It measures the heat produced when the food sample is ignited by an electric spark in the presence of oxygen and platinum which acts as a catalyst. The bomb calorimeter is made of two main parts an inner part in which a measured quantity of food sample to be tested is placed and an outer portion which contains a known volume of water. When the food sample is electrically ignited, the surrounding water absorbs the heat produced. The energy value of the food is calculated by measuring the rise in temperature of water based on the definition of the term calorie. b. Proximate Composition This is a simpler and faster way of determining the calorie content of food. The approximate carbohydrate, fat and protein
2 content of a food given in the food composition tables is multiplied by their fuel factor, i.e., calories provided by 1 g of the nutrient and this total gives the energy value of the food. Carbohydrates 4 kcal Proteins 4 kcal Fats 9 kcal ENERGY NEEDS OF THE BODY The energy requirement for an average healthy person is based on the energy required to carry out basal processes as well as the energy cost of activities one indulges in. The allowances are suggested for a reference man weighing 60kg and a reference woman weighing 50 kg in the 20-39 year age group. Reference Man: The reference man is between 20-39 years of age and weighs 60kg. He is in a state of good health, free from disease, and physically fit for active work. He is moderately active and is employed for 8 hours in moderate work. He spends 8 hours in bed, 4-6 hours sitting or engaged in light work, and 2 hours in walking, active recreation, or household chores. On an average his energy requirement is 2875 kcal. Reference Woman: the reference woman is between 20-39 years of age and weighs 50kg. She is moderately active and spends 8 hours in routine household work. She spends 8 hours in bed, 4-6 hours sitting or moving around and performing light activity, and 2 hours in walking, active recreation, or household chores. On an average her energy requirement is 2225 kcal. BASAL METABOLIC RATE The amount of energy required by the body for carrying out involuntary work and maintaining the body temperature is known as the basal metabolic rate (BMR). The involuntary work includes the functioning of various organs and system which work continuously to keep the body processes going such as the heart and blood circulation, the kidneys and excretion. Approximately one third of this energy is needed for these processes while the remaining two- thirds is utilized for maintenance of muscle tone. Factors affecting the BMR Many factors influence the BMR. a. Body size: Heat is continuously lost through the skin. A tall well built person has a greater skin surface area than shorter or smaller person and loses more heat through the skin and hence has a higher BMR.
3 b. Body composition: The amount of muscle tissue and adipose or fatty tissue in the body affects the BMR. An athlete with well built muscles and little body fat has a higher BMR than a non athlete with more body fat of the same weight. The metabolic activity in muscle tissue or lean tissue is much more as compared to adipose or fatty tissue. c. Age: During periods of rapid growth, the BMR increases by 15-20% because the growth hormone stimulates cell metabolism and new cells are formed. It is high during infancy, pre-school years, and puberty. During pregnancy and location it rapidly increases once again. The BMR gradually decline with age at the rate of 2% for each decade after the age of 21 years. d. Sex: The BMR is 10% higher is male as compared to female. The difference in BMR is attributed to a higher proportion of adipose tissue in females and hormonal variations between the sexes. e. Fever: Fever increases the BMR by 7% for each degree Fahrenheit rise in body temperature. This is one of the reasons for loss of weight during fever. f. State of health: The BMR is low during starvation and malnutrition because of reduction in muscle tissue. In diseases and conditions where catabolic processes are high such as cancers, tuberculosis, and burns, BMR is high. g. Hormones: Disorders of the thyroid gland markedly influence the BMR. Hyperthyroidism, a condition of excessive production of thyroid hormone increases BMR, and hypothyroidism or decreased production of thyroid hormone decreases BMR. h. Climate: BMR rises when the climate is cold in order to maintain normal body temperature. In very warm climates leading to profuse sweating, BMR may increase by trying to reduce body temperature. i. Psychological tension: Worry and anxiety increases BMR. SPECIFIC DYNAMIC ACTION Specific dynamic action (SDA) is a term used to describe the effect food has in increasing the metabolic rate above the level found when fasting. Energy is needed to digest, absorb, and metabolize the food we eat. Food intake stimulates the metabolism process leading to an increase in energy expenditure. This is known as the thermogenic effect of food or the specific dynamic effect. Proteins have maximum effects on SDA, increasing the BMR by about 30% when eaten alone, while carbohydrates and fats show smaller increases. When eaten together in a normal mixed diet, the increase is about 5-10% of basal metabolism.
PHYSICAL ACTIVITY 4 Physical activity increases the energy requirement above the basal metabolism. There is a wide variation in the energy required for physical activity among individuals. Physical activity includes energy needed for work, recreation, and mental activity, i.e., all voluntary activities. Some people use up more energy for physical activity than for basal metabolism. On the basis of occupation, activities are grouped under three heads. Sedentary work teaching, office work, executive, housewife, tailoring. Moderate work farming, industrial labour, driver, maidservant. Heavy work stone cutter, miner, wood cutter. ENERGY BALANCE The human body is constantly using energy which needs to be replaced. For this a constant supply of energy is required. Energy is used for basal metabolism, specific dynamic action, and physical activity. The energy from the food we eat, mainly carbohydrates and fats, is used to meet the energy demands of the body. When food is not available during fasting or starvation, the body draws upon its own stores to meet the energy needs of the body. The body has three types of energy store: i. Glycogen: The form is which carbohydrate is stored in the muscle and liver is adequate to last for 12-48 hours. Approximately 300g glycogen is stored in the muscle and 100g in the liver. ii. Muscle: Protein is stored in limited amounts in the muscle. iii. Adipose tissue: Fat is stored in the adipose tissue and the amount stored varies vastly from one person to another. A person in energy balance neither gains weight nor loses weight. Excessive consumption of calories as compared to the output or activity leads to a condition called over weight, which in severe cases is called obesity. A deficient intake of carbohydrates and fats in the diet leads to underweight or under nutrition. Both underweight and obesity are undesirable conditions which need timely correction. Definition: Energy balance is a condition in which the energy provided by food is nearly equal to the total energy expended by the body resulting in steady body weight. Energy balance: Energy output = Energy input
5 OVERWEIGHT Overweight and obesity affect over 25% adults in developed countries and can lead to serious health consequences if not treated early. When an individual s energy intake consistently exceeds energy expenditure, weight gain occurs initially, leading to obesity. Since energy can neither be created nor destroyed but can be changed from one form to another, the excess chemical energy from food is converted into fat and stored as potential energy in the adipose tissues. Overweight: A person whose body weight is 10% more than the prescribed height for weight standards for his age and sex. Obese: A person whose body weight is 20% or more than that of the prescribed standards. Grossly obese: A person who weighs 45kg or 100% more than accepted standards. Causes of obesity Family food habits rich high calorie foods Ignorant of calorific value of food Skips breakfast, gobbles high calorie snacks Sedentary lifestyle Lower metabolism with increasing age but failure to reduce intake Emotional outlet- eats more to overcome worry, stress, etc. Attend many social events Distress eating ( to avoid wastage) All obese people should lose one to two pounds per week. Physical activity should be increased for faster weight loss and better muscle tone. UNDERWEIGHT Underweight is caused due to under-nutrition which is the result of ingesting insufficient quantity of food. An energy intake less than the need are the most common cause. Other causes for underweight are poor assimilation of food due to digestive disorders, faulty absorption, intestinal infections, poor food habits, stress and tension, poverty and lack of nutrition knowledge. Under nutrition affects ones growth, health, behavior, and brain structure and function. Such individuals should be prescribed a high calorie, high protein, and moderate fat diet for gaining weight. An excess of 500 kcal/day will help in gaining 1 lb/week. BODY MASS INDEX (BMI) The concept of ideal or desirable body weight has been changing from time to time and ideal weight for different body frames was initially computed.
6 Today the weight of an individual is assessed on a more scientific basis known as the body mass index (BMI). BMI is the measure of body fat based on height and weight and applies to an adult man or woman. It is defined as the body mass divided by the square of the body height and is measured in kg/m². Body mass index= weight in kilograms / (height in metres) 2 = W/H 2 Normal BMI is 18.5-25 On the basis of BMI, obesity is graded follows: Obesity BMI Grade 1 25-29 Grade 2 30-40 Grade 3 >40 DIETARY SOURCES All foods provide energy. While selecting food one must consider the other nutrients such as proteins, vitamins, minerals, and fibre present in the food and make a wise choice. The nutrients carbohydrates and fats are consumed mainly as a source of energy. All refined carbohydrates i.e., sugars and starch and all foods rich in fats are rich sources of energy. The cereal group is another excellent source of energy and supplies the highest percentage of calories. Hollow calorie foods Aerated soft drinks Synthetic syrups Candy and candy floss Chocolates Iced cakes and fresh Cream pastries Ice lolly Puff pastry Nutrient dense foods Milk, cheese, yoghurt Green leafy vegetables Pulses, sprouts Soya beans, peanuts Guava, amla Liver, fish, meat Eggs Flax seeds