The total daily energy expenditure (TEE) is an important calculation in the determination of the overall dietary and exercise practices of any person. The amount of energy needed by anyone to meet the daily physical demands will have two components: the amount of energy needed to maintain the body's needs at rest, the basal energy expenditure, expressed as the base metabolic rate (BMR), and the needs generated by the daily activity levels, which include employment, sport, and any other activities.
In general terms, the body will function at a reasonably efficient level where the amount of energy-producing foods consumed is equal to the amount of energy expended. The macronutrients consumed in all diets are the carbohydrates, proteins, and fats present in varying amounts in all foods. As a rule of thumb, a healthy diet will be approximately 60-65% carbohydrates, 12-15% proteins, and less than 30% fats; this standard is subject to deviation to suit individual dietary requirements necessitated by the particular demands of a sport or an existing physiological condition, such as diabetes.
In calculating the total energy expenditure for a given person or the impact of a particular dietary practice on the energy value of the foods consumed, different types of foods have differing values. One gram of a carbohydrate will produce four calories of energy. One gram of a protein will also produce four calories of energy. One gram of fat produces nine calories of energy.
The BMR represents the total daily energy requirements to permit the function of all of the essential body systems, including heart rate, brain function, cardiovascular function, and the work of the thermoregulatory system. The BMR is the energy used by the body at rest. A component of the BMR is the thermic effect, the energy consumed through the ingestion and digestion of food.
Five critical factors will most significantly influence the BMR value for any individual. The first such factor is the body type and body composition of the individual. Heredity plays a role in the determination of the metabolic rate of every person. The second BMR factor is the presence of lean muscle within the body. The body's lean muscle mass has an inherently greater level of metabolic activity than does corresponding body fat tissue. Age is the third factor; the BMR slows by a rate of approximately 2% per decade after age 30. Gender is the fourth factor; females, primarily due to the fact of their typically greater percentage of body fat than males, tend to have a BMR approximately 10% lower than males of similar age and level of fitness. The final BMR factor is a reduction in the body's caloric consumption. When the body is forced to operate on a reduced calorie diet, the body becomes more efficient in the use of the energy sources available to it.
There are a number of methods to determine how many calories of food energy a person requires to simply maintain their BMR. One method, the Harris-Bennet calculation, provides an equation that factors height, weight, and age into a fixed formula, with certain constants provided, calculated in metric measure. This calculation is premised on the fact that a larger person will tend to consume a greater number of calories at rest than would a smaller person. For example, using the Harris-Bennet calculation, a 47-year-old male who is 6 ft 4 in (1.93 m) tall and weighs 190 lb (86 kg) could estimate his BMR as: 66 + (13.7 × 86) + (5 × 193) − (6.87 × 47) ≅ 2,660 calories per day.
While the BMR will vary from person to person, the daily physical activities of an individual are the greatest single factor in energy expenditure. It is an indisputable factor of human function that the more active the individual, the more energy will be expended and the more calories burned from the body's dietary stores. There is significant evidence that the BMR, which is elevated by exercise, will remain elevated from a period of time after the exercise has ceased, causing the body to use more energy than it would otherwise require at rest.
The amount of energy expended during an athletic activity will be determined by the size of the person, the duration, and the intensity of the activity. The total daily energy expenditure will be significantly influenced by these factors. When a person seeks to maintain a particular weight, the total daily energy expenditure can be variable, so long as the caloric consumption remains no greater than the BMR and the TEE combined. One pound of stored body fat (0.5 kg) represents 3,500 calories of potential energy, thus any increase in the TEE or decrease in the daily physical activities that represents a net difference of 500 calories will result in a 1 lb weight loss per week (500 calories per day over seven days).