IntroductionMeasuring energy requirement , expenditure and growth
Body need regular supply of energy to carry out the basic functions. Energy is required for growth, development, organ functioning, thermoregulation and work. Energy measurement are carried out in kilocalorie unit (kcal) or kilojoule (kJ).
Calorie (C) and kcal are often used to denote the same amount of energy expended or derived from food. A kcal or Cal is ''the amount of heat required to raise the temperature of 1 kg of water by 1 degree Celsius''.
Occasionally, kcal is confused with calorie (lower case ''c'' ) which is '' the amount of energy required to increase temperature of one gram of water by 1 ''c''.
However, the SI unit for energy measurement is kilojoules, which is equal to 1000 joules . A joule is defined as ''the amount of energy transferred to an object when a one newton force acts on an object in the direction movement through a distance of one meter''.
Calorie density is the concentration of energy in a defined amount of food. For example, foods enriched with fat have the highest caloric density since fat provides most energy among the nutrient .Likewise, nutrient density is defined as the concentration of nutrient in a given amount of food.
We derive energy from foods and drink in the form of carbohydrates (primary fuel), fats (storage fuel), protein (back up fuel) and alcohol. Fat being most energy dense nutrient provides approximately 9 kcal, followed by carbohydrates (3.75 kcal) and protein (4 kcal) carbohydrates act as a primary fuel for the body while protein and fat sever as back-up and storage fuel, respectively.
The requirements of energy vary among individuals depending upon age, gender, physical activity level, body composition and hormonal status etc. The energy expenditure of individual is the sum of basal metabolic rate (BMR), thermic effect of food and energy utilized in physical activity.
Balance between energy intake and expenditure is helpful to maintain body weight. Any disturbance to this balance, will either lead to loss in weight or weight gain as described in the figure below;
If energy input (intake) is lower than energy output (expenditure) i.e. negative energy balance, it leads to poor growth and development, mobilization of tissue energy reserves and reduced physical activity.
Contrarily, higher energy intake as compared to energy expenditure leads to positive energy balance resulting in obesity and increased risk of certain lifestyle related chronic disease.
Factor affecting energy expenditure
Energy requirement of the body are met in the from of chemical energy (used in metabolic pathway), electrical energy (used in brain and nerve activities), mechanical energy (for body warming). following factor affect the energy needs.
Body size; Body composition and size are the important determinant of energy expenditure. If an individual has more weight, owing to increased BMR/RMR and increased energy needs of larger body, person's caloric needs eventually increase.
Age; The energy expenditure declines with age as the fat free mass decreases over the age. In females decline starts at the age of 40 while in females decline begins ar 50 years. In females the decline is due to excessive fat free mass loss during menopause and overall physical activity decreases after the middle age.
Growth period; Period of growth i.e. periods when new tissues are formed by the body, require additional energy as compared to non-growth phases of life, thus affecting the energy expenditure. Such tissue growth occurs during early years of life (childhood, adolescence), gestation and lactation.
During infancy , there is increased rate of growth, energy requirement is much higher as compared to childhood and adulthood. For example, 35% of the energy is devoted to growth in 1 month old infants while this proportions decreased to 3%only in 12 month old infants.
Physical activity;
Regular physical activity may increase BMR/RMR, leading to higher total daily energy expenditure. It is understood that regular exercise/physical activity helps to maintain energy balance and have a positive effect on lean body mass (particularly skeletal muscles). Moreover, physical activity also regulates the key enzyme responsible for metabolism.
Pregnancy and lactation; Energy needs increase during pregnancy for the growth and development of the fetus, placenta, and maternal tissue. Rise of BMR is attributed to tissues , higher maternal renal, respiratory, and cardiovascular work. during lactation significant proportion of energy (400-500 kcal) is spent in milk production.
Environment; The major determinant of energy expenditure related to environmental is ambient temperature. Shivering and painting contribute to increase energy expenditure in the cold and hot environments respectively. Food intake and physical activity are the behavioral determinants of energy expenditure revenant to environment.
Physiological and genetic influences; Physiological conditions and genetic factor also influence the energy expenditure . Hypothyroidism, muscle atrophy and prolonged fasting decrease energy expenditure while hyperthyroidism, fever burns recovery from major surgery and sepsis increase energy expenditure.
Individual's genes are influenced by the environment they live in and respond differently to specific environment condition, thus affecting appetite and energy expenditure.
Pathological factor; Certain pathological condition can affect energy needs individuals. For example, energy expenditures are decreased during hypothermia and hypothyroidism while fever (13% increase per degree rise in temperature), burns, hyperthyroidism, burns, recovery from surgery and sepsis results in increased energy needs.
What is energy requirement?
Which is the accurate method for measuring energy differences?
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