Basal metabolic rate

Basal metabolic rate, also resting energy requirement, often resting energy consumption, resting energy turnover, basic energy turnover, basic requirement or basal metabolic rate, is the energy per unit time required by an organism to maintain homeostasis.

Basic functions in this context include breathing, blood circulation, thermoregulation and digestion. Energy required for physical activity or heavy sweating is not included in the basal metabolic rate. In physical terms, the basal metabolic rate is a power whose SI unit is the watt. In practice, however, instead of the legal unit of energy, the joule, the obsolete unit of heat, the calorie (usually meaning kilocalorie), is often used and the basal metabolic rate - since it always refers to a whole day, i.e. 24 hours - is accordingly given in kilocalories per 24 hours (kcal/24 h) (whereby the specification "/24 h" is often omitted). In the English-language literature, the term resting energy expenditure (REE) is used for the resting energy requirement.

Scientific literature increasingly formulates the basal metabolic rate using the SI unit megajoule per day (MJ/d) (example: Journal of Nutrition). The Food Information Regulation also prescribes the specification of the physiological calorific value in the unit kJ/100 g in the EU trade in goods, so that the energy balance of foods can also be calculated in the International System of Units (SI) via the quantity balance. There are slightly different factors for the conversion between kilojoules and kilocalories, depending on the definition of the standard conditions. The 9th General Conference on Weights and Measures established the following conversion factor in 1948:

and .

Factors that influence the basal metabolic rate include: Age, gender, body weight, height, muscle mass, heat insulation through clothing and state of health (e.g. increased body temperature due to fever or similar).

Definition

The resting energy requirement is the proportion of the daily energy requirement of an organism that is mathematically allotted to the maintenance of homeostasis at physical rest. This includes, among other things, thermoregulation, the mechanical work of the heart and lungs, the growth of the organism, membrane potential, substrate metabolism and the energy requirements of the brain. In humans, the resting energy requirement accounts for about 50 to 75 % of the total energy requirement (Total Energy Expenditure, TEE). In addition - depending on the individual - there are 15 to 40 % activity-dependent energy requirements and up to 10 % food-induced thermogenesis (NIT). The activity-dependent energy requirement varies according to occupational stress (non-exercise activity thermogenesis NEAT) and leisure activity (= sport, exercise activity thermogenesis, EAT). Food-induced thermogenesis is the energy requirement necessary for the metabolization of the nutrients supplied.

Determination and calculation of the resting energy requirement

The resting energy requirement can be determined using various methods. The most commonly used method is indirect calorimetry. In this method, the oxygen and carbon dioxide concentration is measured in the exhaled air. The amount of carbon dioxide released can be used to determine the energy metabolism. According to a formula by Harris and Benedict, the resting energy requirement can also be calculated. The parameters gender, body weight, body length and age are included in the formula.