Factors influencing energy requirements

Energy from food is measured in kilocalories. You need to ensure you are consuming enough kilocalories to meet the demands of your BMR and PAL, alongside many other factors.

Factors that affect the amount of energy an individual requires can include:


BMR represents roughly 75% of daily energy expenditure. This can influence the energy an individual requires depending on their age, gender, body size and composition (as explained above).

Energy requirements for growth and synthesis of tissues are as follows: During the first three months of life, growth uses about 35% of total energy needs. This falls to 5% at 12 months, reduces to less than 2% in the second year of life and finally to 1–2% until mid-adolescence and 0% by 20 years of age.


Adult males often have about 10-20% more muscle mass than females of the same size and age. Therefore males have a higher BMR as muscle burns more calories than fat, resulting in males requiring about 5-10% more energy than females.


Children and adolescents need more energy for growth and development in comparison to adults. As individuals grow older, their energy requirements reduce as their body composition changes leading to a reduction in BMR. Many people also become less active as they get older.


An individual with an active job such as a personal trainer or a builder will require more energy than an individual with a more sedentary job such as a receptionist in an office.

Physical Activity Levels (PAL)

An active person who exercises daily will require more energy than someone who is inactive, and therefore will have a higher PAL than someone who is less active. If an individual is completing intensive physical training such as running a marathon they will be required to increase their energy intake significantly to meet the demand.


Energy requirements may need to increase to help recover from an illness.

Specific needs

Energy requirements for pregnant or lactating women need to increase slightly (for example, by 200 kilocalories per day during the last trimester of pregnancy) to support the growing foetus and to produce milk for their baby.