Calorie intake and physical activity

The need for calories consumption varies with age, body weight, physical activity and body composition. The last factor is changing dramatically, especially during childhood and adolescence, the ratio between active organs and muscles. Both organs, such as brain, heart, liver and kidney, as the muscle tissue is considered as “low in fat mass and use most of the calories they consume daily, even when well-earned rest (basal metabolism). By contrast, the tissue consumes very little amount of energy. In an infant, muscle tissue is poorly developed and most of the energy is spent on the functioning of the heart, brain, liver, etc., along with new tissue. As your child grows, muscles develop and begin to consume the most energy of the body, while there are significant differences between the sexes. For example, a girl, muscles are 26% of body weight when they are three years old, a figure which increased to 35% at age 18.
As we grow up, the total energy required per kilogram of body weight is decreased gradually and stabilized in adulthood.
Apart from the energy required to support the basic metabolism, children spend extra energy on physical activity as to create new tissue, the digestion of food and absorption of nutrients after a meal.

Energy consumption from the physical activity varies greatly from child to child and from day to day. A 10-year-old boy makes a sedentary life, weighs 40 pounds and watches TV three hours a day without doing sports, do not need more than 1670 calories (7000 kJ). By contrast, the same boy, with a more active lifestyle (ie one hour of intense exercise a day) may need 2390 calories (10000 kJ).