Chapter 2 :- Energy

(A.) Definition of Energy and Units of its measurement (Kcal) :-

Energy:- The ability to do work. Energy from food is expressed in kilocalories and kilojoules.

Food energy is defined as the energy released from carbohydrates, fats, proteins, and other organic compounds. When the three major calorigenic nutrients (carbohydrates, fats, and proteins) in food are burnt entirely with sufficient amounts of oxygen, it releases energy or food calories.

Fats have the greatest amount of food energy per mass, up to 9 kcal g−1. Most of the carbohydrates and proteins have approximately 4 kcal g−1, whereas fibers have less due to its low digestibility and absorbance in human bodies.

Energy formed in mitochondria of the cell is actually stored in our liver and muscle cells and readily available as glycogen.

The energy from the breakdown of food is stored in the body in the form of a high energy compound, adenosine triphosphate (ATP). ATP is also known as energy currency. ATP acts as a store of energy-rich phosphate bonds. A living cell can use energy only in the form of energy-rich phosphate bonds. When energy is required ATP is converted to ADP. One mole of ATP provides 8 kcals 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. The kilocalorie is defined as the amount of heat required to raise the temperature of 1 kg (1,000 g) of water by 1°C. This calorie is 1,000 times bigger than the calorie used in physics. 

        The international unit for energy is the joule ( J) and it is the energy expanded when 1 kilogram (kg) is moved 1 metre (m) by a force of 1 newton (N).

Kilojoule (kJ = 10³ J ), or megajoule (MJ = 10⁶ J) .

1 kilocalorie = 4.184 kilojoules 

1 megajoule = 239 kilojoules 

(B.) Energy contribution from macronutrients (Carbohydrates, Proteins, and Fats) :-

The dietary macronutrients include carbohydrates, proteins, and fat are the major sources of energy in our diet. Food energy is necessary for biological functions including protein synthesis; maintenance of body temperature, cardiac output, respiration, and muscle function; and storage and metabolism. In our daily life, we do a lot of physical and mental activities that also require a lot of energy and these energy requirements fulfilled by macronutrients.

Energy:-

Energy is the capacity to do work.
In biology, energy is often stored by cells in biomolecules, like carbohydrates (sugars) and lipids. The energy is released when these molecules have been oxidized during cellular respiration. The energy released from them when they are oxidized during cellular respiration is carried and transported by an energy-carrier molecule called ATP (Adenosine Triphosphate).

Let’s see the energy contribution from macronutrients:

Carbohydrate:-

Dietary carbohydrates are involved in the control of energy balance because the regulation of food intake depends, in part, on the carbohydrate need of the individual. Because there is an obligatory requirement for glucose in several organs such as the brain, a spontaneous increase in food intake is seen when the diet has a low-carbohydrate, high-fat content.

While the amount of carbohydrate required to avoid ketosis is very small (about 50 g/day), carbohydrate provides the majority of energy in the diets of most people. An optimum diet should consist of at least 55% of total energy coming from carbohydrates obtained from a variety of food sources. In arriving at its recommendation of a minimum of 55% of total energy from carbohydrate, the consultation realized that a significant percentage of total energy needs to be provided by protein and fat, but that their contribution to total energy intakes will vary from one country to another based on food consumption patterns and food availability.

Protein:-

Proteins are essential nutrients for the human body. Protein provides the body with approximately 10 to 15% of its dietary energy and it is the second most abundant compound in the body, following water.

Proteins are one of the building blocks of body tissue and can also serve as a fuel source. As a fuel, proteins provide as much energy density as carbohydrates: 4 kcal (17 kJ) per gram; in contrast, lipids provide 9 kcal (37 kJ) per gram. Physical activity and exertion as well as enhanced muscular mass increase the need for protein. If not enough energy is taken in through diet, as in the process of starvation, the body will use protein from the muscle mass to meet its energy needs, leading to muscle wasting over time. If the individual does not consume adequate protein in nutrition, then the muscle will also waste as more vital cellular processes (e.g., respiration enzymes, blood cells) recycle muscle protein for their requirement.

While carbohydrates are indeed the body’s preferred source of fuel, protein plays an important part in the energy and muscle preservation needs of endurance athletes. Protein is mainly known for its role in the repair, maintenance, and growth of body tissues, but it also has a role in energy supply. After about 90 minutes of exercise in well-trained athletes, muscle glycogen stores become nearly depleted, and the body will look for alternative fuel sources. Our muscle tissue becomes a target for a process called gluconeogenesis, which is the synthesis of glucose from the fatty and amino acids of lean muscle tissue.

Fat:-

Fats are the slowest source of energy but the most energy-efficient form of food. Each gram of fat supplies the body with about 9 calories, more than twice that supplied by proteins or carbohydrates. Because fats are such an efficient form of energy, the body stores any excess energy as fat. The body deposits excess fat in the abdomen (omental fat) and under the skin (subcutaneous fat) to use when it needs more energy. The body may also deposit excess fat in blood vessels and within organs, where it can block blood flow and damage organs, often causing serious disorders.

The amount of energy stored in the form of fat is large, representing 92–98% of all endogenously stored energy with CHO contributing only about 2–8%. Fat is at the bottom of an oxidative hierarchy that determines fuel selection, and its oxidation is governed by the presence or absence of the other macronutrients. Besides, the rate at which it can be oxidized depends on the intensity of energy expenditure.

Fat should be limited to less than about 28% of daily total calories (or fewer than 90 grams per day).
Saturated fats should be limited to less than 8%.

Nutrients & Energy Value

• Kilocalorie (kcal) and kilojoule (kJ) are measuring units for energy.
• 1 Kcal is approximately equal to 4.2 KJ.

Nutrient	Energy Value
Carbohydrate	17kJ (4 kcal) per gram
Protein	17kJ (4 kcal) per gram
Fat	37kJ (9 kcal) per gram

The energy requirements of individuals vary according to several factors, including the thermic effect of food (the energy required to process foods), the basal metabolic rate, the physical activity level, food availability and climate as well.

Macronutrient distribution range

Macronutrient	Distribution range
carbohydrate	45%-65% of energy
protein	10%-35% of energy
fat	20%-35% of energy

(C.) 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 -

1. Sedentary work – teaching, office work, executive, housewife, tailoring. 
2. Moderate work – farming, industrial labour, driver, maidservant. 
3. 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.

(D.) Concept of BMR, SDA, Thermodynamic action of food:-

BMR (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 systems 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:- 

Body Size:- Heat is continuously lost through the skin. A tall well-built person has a greater skin surface area than a 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 athletic 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 percent 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 declines with age at the rate of 2 percent for each decade after the age of 21 years.

Sex:- The BMR is 10 percent higher in men as compared to women. The difference in BMR is attributed to a higher proportion of adipose tissue in females and hormonal variations between the sexes.

Fever:- Fever increases the BMR by 7 percent 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 hyperthyroidism or decreased production of thyroid hormone decreases BMR. 

Climate:- The 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 increase BMR.

Specific Dynamic Action (SDA):- 

• 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 effect on SDA, increasing the BMR by about 30 percent when eaten alone, while carbohydrates and fats show smaller increases. When eaten together in a normal mixed diet, the increase is about 5-10 percent of basal metabolism. 

Physical Activity:-

Physical activity increases the energy requirement above basal metabolism. There is a wide variation in the energy required for physical activity among individuals. Physical activity includes the 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 labor, driver, maidservant.
• Heavy work – stone cutter, miner, woodcutter.

(E.) Dietary sources of energy:-

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 or empty calories are provided by food which is rich in energy but lack other vital nutrients. Sugars, fats, and alcoholic beverages are referred to as empty-calorie foods because they contain traces of vitamins and minerals. They are low in nutrient density. 

• Aerated soft drinks 
• Synthetic syrups
• Candy and candy floss
• Chocolates 
• Iced cakes and fresh cream pastries 
• Ice lolly
• Puff pastry 

Nutrient-dense foods are those food which are rich in one or more nutrients apart from calories. It is a measure of the quantity of these nutrients supplied by a food in relation to its calorie content. Nutrient-dense foods are of special importance to weight watchers and those leading a sedentary lifestyle. It helps them get all the nutrients they need without consuming unnecessary calorie-rich foods and gaining weight. 

• Milk,cheese, yoghurt 
• Green leafy vegetables 
• Pulses, sprouts 
• Soya beans,peanuts
• Guava, amla
• Liver,fish, meat
• Eggs
• Flaxseeds

(F.) Concept of energy balance and the health hazards associated with Underweight, Overweight:-

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 stores to meet the energy needs of the body.

The body has three types of energy store:

Glycogen: The form in 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 overweight, which in severe cases is called obesity. The deficient
intake of carbohydrates and fats in the diet leads to underweight or undernutrition. Both underweight and obesity are undesirable conditions that 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

Overweight:- Overweight and obesity affect over 25 percent 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 percent more than the prescribed height for weight standards for his age and sex.

Obese A person whose body weight is 20 percent or more than that of the prescribed standards. 

Grossly obese A person who weighs 45 kg or 100 percent more than accepted standards. 

Underweight A person whose weight is 15-20 percent below the accepted standards. 

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) = Weight in                                                          kilograms/(Height in metres)²

Normal BMI of men = 20-25 or women= 19-24 

Values over 25 indicate obesity. 

Causes of obesity:-

• Family food habits-rich high-calorie foods
• Ignorant of calorific value of food
• Skips breakfast, nibbles high-calorie snacks 
• Sedentary lifestyle 
• Lower metabolism with increasing age but failure to reduce intake 
• Emotional outlet- eats more to overcome worry, stress, etc.
• Attends many social events 
• Distress eating (to avoid wastage)

An obese person should lose one to two pounds per week. A reduction of 500 kcal/day will lead to a weight loss of one pound per week. Physical activity should be increased for faster weight loss and better muscle tone. 

If 1 lb weight is to be lost per week, then 

1 lb of body fat = 455 g

1 g of body fat provides 7.7 kcal/g as it has some water in it.

Calorie equivalent of

1 lb body fat = 455 × 7.7 = 3,500 kcal

3,500 kcal to be lost in 1 week or 7 days

:. Weight loss in 1 day = 3,500/7 = 500 kcal/day

Underweight:- Underweight is caused due to undernutrition which is the result of ingesting insufficient quantity of food. An energy intake less than the need is the most common cause. Other causes for underweight are poor assimilation of food due to digestive disorders, faulty absorption, intestinal infestations, infections, poor food habits, stress and tension, poverty, and lack of nutrition knowledge. 

            Teenagers are weight conscious and skip meals or consume junk food to maintain their weight. Anorexia nervosa is a condition of self-induced severe weight loss seen in adolescents and has psychological origins.

            Undernutrition affects one's growth, health, behaviour, and brain structure and function. Such individuals should be prescribed a high-calorie ,high-protein,moderate-fat diet for gaining weight. An excess of 500 kcal/day will help in gaining 1 lb/week.

Key Terms:-

• Basal Metabolism:- The energy needed by the body to carry out involuntary activities while at rest.
• Calorimeters:- An instrument used to measure heat energy by noting the rise in temperature of a known volume of water. 
• Specific dynamic action:- Also known as post-prandial thermogenesis or calorigenic effect of food. It is the energy required to transform food into nutrients to be used by body cells and accounts for 6-10 percent increase in energy expenditure.