Unit 2 - ENERGY

Introduction

Energy is defined as the ability to do work. Energy exists in several forms. The forms of energy important in nutrition are:

• Chemical energy in food. 
• Light or solar energy for synthesis of vitamin D in the skin and for photosynthesis is plants. 
• Mechanical energy for movement of muscles. 
• Electrical energy for functioning of the brain and Nerve cells. 
• Heat energy, generally produced when energy is converted from one form to another. 
• The energy from food is finally converted into heat energy. 

Forms of 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.. 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= 103J), or megajoule (MJ=106J) to express energy.
• 1 kilocalorie = 1 calories
• 1 kilocalorie = 4.184 or 4.2 kilojoules

ENERGY VALUE OF FOOD

The energy content of various foods can be measured in two ways: by calorimetry or by proximate composition.

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.

Working of bomb calorimeter

Proximate Composition

This is a simpler and faster way of determining the calorie content of food. The approximate carbohydrate, fat and protein 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

To calculate the energy available from a food, multiply the number of grams of carbohydrate, protein, and fat by 4,4, and 9, respectively. Then add the results together.
For example, 1 slice of bread with a tablespoon of peanut butter on it contains 16 grams carbohydrate, 7 grams protein, and 9 grams fat :
16g carbohydrate x 4 kcal/g =      64 kcal
7g protein x 4 kcal/g =      28 kcal
9g fat x 9kcal/g =      81 kcal
Total = 173 kcal

Energy contribution from macronutrients

• Macronutrients give us energy.
• Although each of these macronutrients supplies the energy needed to run body functions, the amount of energy that each provides varies.
• Carbohydrates and proteins each provide 17kJ/g whereas fats provide 37kJ/g. 1 kilojoule (kJ) = 1000 joules.
• 4.2 joules is the energy needed to raise the  temperature of 1g of water by 1°C.
• A balance of energy-giving nutrients is suggested.

Pie chart showing percentage amounts of  macronutrients in a well balanced diet.

Why do we need carbohydrates?

• Carbohydrates, in the form of starches and sugars, are the macronutrients required in the largest amounts. When eaten and broken down, carbohydrates provide the major source of energy to fuel our daily activities. It is recommended that carbohydrates should supply 45–65% of our total daily energy needs.
• Some of the carbohydrate we consume is converted into a type of starch known as glycogen, which is stored in the liver and muscles for later use as an energy source.
• Not all of the carbohydrates found in foods are digestible. For example, cellulose is a non-digestible carbohydrate present in fruits and vegetables. Although unable to be used as an energy source, this type of carbohydrate plays a very important role in maintaining the health of the large intestine and assisting with the removal of body waste. It is often referred to as ‘dietary fibre’.

Why do we need proteins?

• The proteins we consume as a part of our diet are broken down in the gut to amino acids. The body can then use these amino acids in 3 main ways:
• As ‘building blocks’ in the production of ‘new’ proteins needed for growth and repair of tissues, making essential hormones and enzymes and supporting immune function.
• As an energy source.
• As starting materials in the production of other compounds needed by the body.
• Protein in the diet that comes from animal sources contains all of the essential amino acids needed, whereas plant sources of protein do not. However, by eating a variety of plant sources, the essential amino acids can be supplied.

Why do we need fats?

• Although fats have received a bad reputation in relation to heart disease and weight gain, some fat in the diet is essential for health and wellbeing.
• It is recommended that 20–35% of our daily energy requirement should be supplied through the consumption of fats and oils. In addition to supplying energy, fats are needed to:
• Supply fatty acids that the body needs but cannot make (such as omega-3)
• Assist with absorption of the fat-soluble vitamins A, D, E and K and carotenoids
• Provide foods with flavour and texture.
• *carotenoids - any of a class of mainly yellow, orange, or red fat-soluble pigments, including carotene, which give colour to plant parts such as ripe tomatoes and autumn leaves.
• Dietary fats are of 3 main types:
• Saturated fat – found in foods like meat, butter and cream (animal sources).
• Unsaturated fat – found in foods like olive oil, avocados, nuts and canola oil (plant sources)
• Trans fats – found in commercially produced baked goods, snack foods, fast foods and some margarines.
• Replacing saturated fats and trans fats in the diet with unsaturated fats has been shown to decrease the risk of developing heart disease.

ENERGY NEEDS OF THE BODY

The rate of energy release from macronutrients by chemical processes occurring in the body is known as metabolic rate.
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.
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.
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.
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.
Gender: The BMR is 10% higher in males as compared to females. The difference in BMR is attributed to a higher proportion of adipose tissue in females and hormonal variations between the genders.
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.
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.
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.
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.
Psychological tension: Worry and anxiety increases BMR.

SPECIFIC DYNAMIC ACTION

• Specific dynamic action (SDA) of a food represents the effort or energy that the body has to use to break down the food until it is reduced to its basic unit, which is the only form in which it can enter the bloodstream. 
• Also known as thermic effect of food (TEF) or dietary induced thermogenesis (DIT).
• 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

• 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

• 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
• 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.
• 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.
• Muscle: Protein is stored in limited amounts in the muscle.
• 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.

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.

Health Risks of Being Overweight

• Excess weight may increase the risk for many health problems, including
• type 2 diabetes
• high blood pressure
• heart disease and strokes
• certain types of cancer
• sleep apnea
• osteoarthritis
• fatty liver disease
• kidney disease
• pregnancy problems, such as high blood sugar during pregnancy, high blood pressure, and increased risk for cesarean delivery (C-section)

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 0.45kg/week.

Causes of under weight

• Hyperthyroidism
• Cancer
• Tuberculosis
• Diabetes
• HIV/AIDS
• Anorexia
• Bulimia
• Medication
• Excessive Physical Activity
• Excessive Stress
• Coeliac Disease (Gluten Allergy)

Health Risks of Being under weight

• malnutrition, vitamin deficiencies, or anemia
• osteoporosis from too little vitamin D and calcium
• decreased immune function
• increased risk for complications from surgery
• fertility issues caused by irregular menstrual cycles
• growth and development issues, especially in children and teenagers

BODY MASS INDEX

• 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. 
• Today the weight of an individual is assessed on a more scientific basis known as the body mass index (BMI).
• Body Mass Index (BMI) is a measure of body fat based on height and weight.
• Body mass index= weight in kilograms / (height in metres)2 = W/H2

On the basis of BMI, obesity is graded as 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 calories VS NUTRIENT DENSE FOODS

Factors affecting energy requirements

• BMR – A living body needs a minimum number of calories to maintain vital functions, such as breathing and keeping the heart beating.  This minimum number of calories is called Basal Metabolic Rate (BMR). A quick way to approximate your BMR is to multiply your current weight by 10 for females and by 11 for males.
• AGE – Energy requirement needs peak up at about the age of 25 yrs and then declines by 2 % every 10 years. The aging body replaces muscle with fat, which burns fewer calories than muscle does. Staying active and doing exercises keeps muscle mass intact.
• GENDER - An adult man has less body fat and about 10 to 20 % more muscle than a woman of the same size and age. Muscles burn more calories than fats does, a man’s energy requirement is about 5 to 10 % more than a woman’s.
• OCCUPATION  
• Sedentary work – teaching, office work, executive, housewife, tailoring. 
• Moderate work – farming, industrial labour, driver, maidservant. 
• Heavy work – stone cutter, miner, wood cutter. 
• HEALTH – Energy requirement increases during sickness or ill health.
• BODY SIZE - Our body shape and size affect the energy requirement you need because muscle burns more calories than body fat does. If your body has a greater proportion of muscle to fat, your metabolism is higher.  If your body has more fat than muscle, your metabolism is lower and you tend to store fat in the body.
• ENVIRONMENTAL TEMPERATURE – People living in colder climate require more energy to burn more calories so as to maintain the normal body temperature as compared to people staying in warmer climate

CONCLUSION

• The body requires a continuous source of energy to stay alive and to carry out all body functions, processes and activities.
• This energy is derived from the oxidation of carbohydrates, proteins and fats in the tissue cells resulting in the production of heat energy.
• The body is in need of energy to carry out the involuntary work of the body or for the basal metabolism.
• The body is in energy balance if there is no weight loss or weight gain.
• Overweight and obesity result from an imbalance between energy intake, which is more and energy output, which is less.
• Underweight results from deficient intake and more output.
• Both conditions can be cured by modifying the energy intake.