4.3 understand that energy requirements vary with activity levels, age and pregnancy

Age/sex/occupation of person	Energy needed per day
Newborn baby	2000
Child aged 2	5000
Child aged 6	7500
Girl aged 12-14	9000
Boy aged 12-14	11000
Girl aged 15-17	9000
Boy aged 15-17	12000
Office worker	9500-10500
Heavy manual worker	15000
Pregnant woman	10000
Breast-feeding woman	11300

Energy is needed for all movement as wells as for keeping the body warm, for heartbeat, to allow messages to be sent through nerves and other body functions. However, the amount of energy needed also depends on the physical work, age, sex and condition.

Boys need more energy than girls in general and pregnant women need more energy due to the fetus. 

The amount of physical work done also varies energy requirements

Not only does the energy requirement vary, the content of the diet may vary too. For example, during pregnancy, a woman may need extra iron and calcium to aid the growth of the fetus. In younger women, the blood loss during menstruation can result in anemia (blood does not carry much oxygen) and hence need extra iron to compensate for blood loss.