What is energy in foods?

Energy :

Our body needs a balance in energy. Energy balance in an individual depends on his or her dietary energy intake and energy expenditure. Imbalance in energy intake and expenditure results in gain or loss of body components resulting in changes in body weight. Excess energy cannot be eliminated, and is eventually deposited in the form of body fat which results in obesity.

Energy is calculated in Calories and calories are obtained from food. We calculate the energy (calories ) given by one food using the contents of the food.

The Estimated Energy Requirement (EER) is the average dietary energy intake that is predicted to maintain energy balance in a healthy, adult of a defined age, gender, weight, height, and level of physical activity consistent with good health.

So energy requirements vary by each individual and so average energy estimation helps to set a normal standard for people. Energy requirements also depends on each persons' Basal metabolic rate (BMR).

To calculate ones energy requirements we need to know Basal Energy Expenditure (BEE) ,Diet induced Energy Expenditure (DEE) and Activity-induced Energy Expenditure (AEE)
BEE refers to the metabolic activity necessary to sustain life (i.e., respiration, pulse, body temperature) or the energy needed in resting condition and can be estimated using the following equation:
Harris-Benedict equation:
BEE(kcal/day):Males = 66.5 + (13.7 X W) + (5.0 X H) - (6.8 X A)
Females = 655 + (9.6 X W ) + (1.7 X H) - (4.7 X A)
where:
W = usual or adjusted weight in kilograms
H = height in centimeters
A = age in years

Diet -induced Energy Expenditure includes energy costs of food absorption, metabolism and storage. DEE in individuals is relatively small and doesnot make important contirbution in energy balance.
Total energy Expenditure (TEE) = BEE + Activity-induced Energy Expenditure (Physical activity,PA )

Or the total energy expenditure is calculated by multiplying BEE with PA factor.

The physical activity factor varies between individuals depending on the duration and intensity of activities they perform. The PA factor vaires from 1.2 - 2.2 between individuals 18 and 64 year old healthy adults. On an average it is estimated the people having western life style ,regular ,relatively sedentary lifestyle have PA between 1.2-1.6 and that of elite athelets can be greater than 2.5

On an average the energy needed by individual is given below.
Men ~2300-2600 kcal
Women ~1900-2200 kcal
Pregnant +500 kcal

Lactating +600 kcal