diet and metabolic rate
carbohydrates - to release energy, fats to keep warm and release energy, protein for growth, cell repair and cell replacement, fibre to keep things running smoothly through the digestive system, vitamins and mineral ions to keep your skin, bones blood and everything generally healthy
you need energy to fuel the chemical reactions in the body to keep you alive. these reactions are your metabolism and the speed at which they occur is called your metabolic rate.
peoples energy needs vary because of who they are