Diet Therapy Health Article

Energy requirements

Carbohydrates, proteins, and fats provide energy in the form of calories to fuel the body for metabolic processes, growth, and activity. When an individual consumes as many calories each day as the body uses, they are in a state of energy balance and will neither gain nor lose weight. When more calories are eaten than the body uses, the excess calories are stored as fat and weight increases. On the other hand, when fewer calories are consumed than the body needs, stored fat is burned and weight decreases. Using the metric system nomenclature, a kilojoule (kJ) is used instead of a kilocalorie (kcal), where 1 kcal=4.184 kJ and 1 megajoule (MJ)=1000 kJ.

The amount of energy required depends on such factors as an individual's weight, gender, age, and activity level, so an estimation should be made based on these parameters. Some dietary guidelines do suggest an average energy intake for people in different age groups, but many of the guidelines do not base the estimations on measures such as activity level. The Food and Agriculture Organization/World Health Organization uses a more accurate method for estimating energy requirements for populations and individuals. They define energy requirement as "... the amount of energy needed to maintain health, growth, and an appropriate level of physical activity." The "appropriate level of physical activity" is not a standardized level, but is dependent on social, cultural, and lifestyle factors. Physical activity categories for light, moderate activity or heavy work are used to provide a better energy estimation. For example, a 143 lb (65 kg) woman between the ages of 30-60 years who participates in light activity would require about 2190 kcal/day (9.2 MJ/day). At a moderate activity level, this same woman would require approximately 2300 kcal/day (9.6 MJ/day) and 2550 kcal/day (10.7 MJ/day) for heavy activity.