Energy - Nutrition

 

 

ENERGY

Energy is defined as the ability to do the 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 skin and for photosynthesis in plants,

·         Mechanical energy for movement of muscles,

·         Electrical energy for functioning of brain and nerve cells; and

·         Heat energy, generally produced when energy is converted from one form to another.

 

The energy present in food or the energy needed by the body is measured in units called joules or calories.

The Kilocalorie is defined as the amount of heat required to raise the temperature of 1kg of water by 1^o C i.e. from 14.5 to 15.5 degree Celsius.

Joule is the energy that is expended when 1 kilogram (kg) is moved 1 metre (m) by a force of 1 newton (N).

1 kilocalorie = 4.184 kilojoules

1 megajoule = 239 kilocalories

 

Food is digested, the complex nutrients i.e., carbohydrates, fats, protein are broken down into monosaccharides, fatty acids & glycerol, & amino acids, respectively. These simple forms are absorbed into the blood stream & supplied to the millions of cells in the body to be oxidized by series of complex steps to release energy.

Human being needs energy for the following:

• Basal metabolism

• Metabolic responses to food – thermo genesis / SDA

• Physical activities

• Growth

• For mothers in special conditions (pregnancy & lactation)

 

Total Energy needed by the body = BMR + SDA + Activity

Basal Metabolic Rate (BMR): The amount of energy required by the body for carrying out involuntary work and maintaining the body temperature is known as BMR. The involuntary work includes the functioning of various organs and systems which work continuously to keep the body processes going such as heart and blood circulation, the kidneys and excretion. Approximately one-third of this energy is needed for these processes while the remaining two-third is utilized for maintenance of muscle tone.

Factors affecting the BMR:

BMR is the largest component of the daily energy demand representing 45 – 70 percent of daily total energy expenditure. It is highly variable & the cause of this variation includes factors such as:

 

·         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 athlete with well-built muscle 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 lactation it rapidly increases once again. The BMR gradually declines with age at the rate of 2% for each decade after the age of 21 years.

     ·         Sex: 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 variation between                 the sexes.

·         Fever: Fever increases the BMR by 7% for each degree. 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 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 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): It 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 thermogenic effect of food or the Specific dynamic effect. Proteins have the maximum effect 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 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.

 

·         Sedentary workers –persons taking, reading, watching TV, listening Radio, doing computer works specially sitting activities (teachers, office workers).

·         Moderate workers – with some activity’s servants, house cleaners, rural women, students etc.

·        Heavy workers – Labour class.

 The energy requirement varies with the type of the activity and the speed and efficiency with which it is performed. For example, walking briskly uses thrice the energy of walking at moderate pace. The larger the body size, the more energy would be needed just as more energy is needed to move a heavy sack of potatoes compared to a lighter one.

Energy requirement

The amount of food needed to ensure good health will vary from one individual to another. All people do not require the same amount of nutrients.

Requirements vary depending upon age, gender, body size, activities, state of health etc.

ICMR has prepared Recommended Dietary Allowances (RDA) for Indians.

 The body has three types of energy store.

Glycogen – The form in which carbohydrate is stored in the muscles and liver is adequate to last for 12-48 hours. Approx 300 g glycogen is stored in the muscle and 100 g 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.

Energy balance: Energy output – Energy input

Energy balance is a condition in which the energy provided by food is nearly equal to energy expenditure by the body resulting in a steady body weight.

Overweight & underweight both are the abnormalities and both are measured by BMI (body Mass Index)

 

BMI = Weight in kilograms / height in meters²

W/H²

^{Normal values of BMI for Men = 20-25}

^{For Women= 19-24}

^{Values over 25 indicate obesity.}

Obesity Grade I: BMI 25-29

Grade II: BMI 30-40

Grade III: BMI >40