An individual remains healthy when all the metabolic activities are going on smoothly in his body. All of us require energy to carry on the voluntary and involuntary body functions. The energy requirements vary among different individuals. These variations are due mainly to the differences in their muscular activities. Certain other factors like body temperature, environmental changes, type of food taken, different physiological and emotional states also account for variations in energy requirements. Energy is measured in terms of calories.
A calorie is the amount of heat required to raise the temperature of 1 gm of water through 1°C rise in temperature. A physiological calorie is a thousand times more than the physics calorie. The food calorie is hence known as a kilocalorie.
A minimum number of calories are required to carry on the basic involuntary functions of the body. The rate at which the calories are required to carry on these functions is known as Basic Metabolic Rate of the individual and is commonly written as BMR. The BMR can be defined as the “energy expenditure of the organism in a state of complete mental and physical rest”. It can also be defined as the “rate at which a body is carrying on its overall cellular metabolism at basal conditions”. Basal conditions are described as the post absorption state (12 hrs. to 15 hrs. after meals), physically and mentally at rest in reclining position in bed, in a room with a temperature of 25°C and having comfortable humidity.
The output of energy and consumption of oxygen by the living organism are dependent upon its muscular activity and other factors like the nature of food consumed, body temperature, emotional state of mind as well as age and sex variations. The BMR can be measured by direct and indirect methods (Spirometer readings).
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Factors influencing BMR
The basal metabolic rate depends upon the body surface area and weight. In the case of a one year old baby weighing 10 kg having a surface area of 0.50 sq. m the surface area per unit body weight will be 0.05 sq m/kg while in the case of a 25-year old adult weighing 70 kg and having 1.8 sq. m surface area, the surface area per unit body weight will be 0.026 sq. m/kg (1.8 ÷70).
We, therefore, conclude that children have larger surface area per unit body weight. This accounts for a higher BMR in the case of children.
The BMR decreases as children grow older. Hence age is one of the factors affecting the basic requirements of calories. Boys are more vigorous than girls. The BMR in the case of males is higher than the females. In cold climates the BMR rises, while in warm weather the BMR goes down. During conditions of under nutrition and starvation, there is a general decline in the body activities that accounts for a lower BMR. The energy requirement increases when an individual has fever. Every degree of rise in temperature calls for a 12% increase in the BMR. Hormonal secretions affect the BMR of the individual. A person suffering from hypothyroidism has a lower BMR and is low and sluggish in his movements. A normal adult requires 1 calory of energy per kilogram of body weight each hour to carry on with the basic involuntary functions. The BMR of an adult weighing 50 kg will be 1×24×50=1200 calories.