What is the Basal Metabolic Rate?
Basal Metabolic Rate (BMR) refers to the energy metabolism rate when the human body is awake and extremely quiet, without being affected by muscle activity, ambient temperature, food, and mental stress [1] . That is, during basic physiological activities (ie, blood circulation, breathing, and constant body temperature), the minimum calorie consumption per unit surface area minus the standard calorie consumption, and the percentage of the difference between the standard calorie consumption and the standard calorie consumption is called basal metabolic rate [1] .
- Chinese name
- Basal metabolic rate
- Foreign name
- basal metabolic rate
- Short name
- BMR
- Definition
- Basal metabolism per unit of time
- Influencing factors
- Age, gender, ambient temperature, climate
- Clinical application
- Diagnosing a Thyroid Disease
- Basal Metabolic Rate (BMR) refers to the energy metabolism rate when the human body is awake and extremely quiet, without being affected by muscle activity, ambient temperature, food, and mental stress [1] . That is, during basic physiological activities (ie, blood circulation, breathing, and constant body temperature), the minimum calorie consumption per unit surface area minus the standard calorie consumption, and the percentage of the difference between the standard calorie consumption and the standard calorie consumption is called basal metabolic rate [1] .
- To measure the basal metabolic rate, before resting in the morning, rest for half an hour (but stay awake), maintain the room temperature above 20 , and use the indirect calorimetry method to measure. The unit of basal metabolic rate is kJ / (m 2 · h) (kJ / m2 / h), which is the number of kilojoules of heat emitted per square meter of body surface per hour [2] .
Introduction to Basal Metabolic Rate
- Basal metabolic rate, simply put, basal metabolism per unit time is called basal metabolic rate, which refers to the energy metabolism of the human body in a basic state, and the basic state refers to a person who is awake and very quiet, free from muscle activity, Factors such as ambient temperature, food, and mental stress affect your condition. . It is normal if it does not exceed or fall below 15% of the normal value. The measurement of basal metabolic rate is the main auxiliary method for clinical diagnosis of thyroid disease. When the thyroid function is hyperactive, the basal metabolic rate can be significantly increased, and when the thyroid function is low, the basal metabolic rate is significantly reduced.
- In clinical and physiological experiments, subjects were required to have not eaten food for at least 12 hours, rest at rest at room temperature of 20 ° C for half an hour, stay awake, and measure metabolic rate without performing mental and physical activities. [3]
Basal metabolic rate measurement principle
- According to the law of conservation of energy, the energy consumed by the body should be equal to the sum of the thermal energy generated and the external work done. If the body does not perform external work for a certain period of time, the energy consumed is equal to the thermal energy generated in a unit time. Since the human body temperature is constant, the heat output per unit time should be equal to the total heat emitted to the outside world. Therefore, by measuring the total heat emitted by the body within a certain time, the body's energy metabolism rate can be known [3] .
Basal metabolic rate measurement method
- Based on the above measurement principles and continuous research and testing, researchers at home and abroad have summarized three methods for determining BMR: direct calorimetry, indirect calorimetry, and formula estimation. The first two methods are the "gold standard" for measuring energy consumption, and the formula inference method is simpler and faster than the first two methods, and is suitable for the estimation of BMR in large sample populations [3] .
Direct calorimetry
- The direct calorimetry method is to place the subject in a special testing environment, collect the total heat emitted by the subject within a certain period of time (through radiation, conduction, convection and evaporation), and then convert it into unit time. The amount of metabolism, that is, the energy metabolic rate. However, the device for direct calorimetry is more complicated, and it is mainly used to study obesity and endocrine system disorders. The measurement of the general population mainly adopts the latter two methods [3] .
Basal metabolic rate indirect calorimetry
- Indirect calorimetry is easier to measure than direct calorimetry, and more accurate than formula inference. It is a method of measuring BMR that has attracted much attention in recent years. Its principle is to calculate the energy consumption by measuring the oxygen consumption and carbon dioxide generation under specific conditions and within a certain period of time based on the constant relationship between the oxygen consumed by the three major production nutrients and the carbon dioxide produced at the time of production [3] .
- The analysis system used in recent years for the gas metabolism analyzer (also known as the cardiopulmonary function tester) is a non-invasive indirect calorimetry system commonly used internationally and has been widely used in experimental and clinical research. Using indirect calorimeter to carry out BMR measurement can not only be used to study the nutritional requirements of the population, but also more suitable for clinical diagnosis and treatment of metabolic-related diseases or the need for accurate assessment of energy in nutritional support for various diseases, analysis of energy sources and nutritional support effects To develop individualized applications [3] .
Basal Metabolic Rate Formula
- Advances in indirect calorimetry and equipment have provided feasibility for accurate assessment of human BMR. However, like direct calorimetry, there are problems such as expensive equipment, long measurement time, and complex instrument operation. Therefore, after years of research, researchers have proposed various formulas to predict the BMR of the population. The formula inference method requires only simple anthropometric measurements to evaluate basal metabolism, which is convenient for clinical practice, public health, and sports medicine, and for conducting large-scale population research [3] .
Basal metabolic rate calculation formula
- There are many formulas for calculating the basal metabolic rate, which correspond to different methods. Only three of them are listed below. The most commonly used method is the first method. It is more reliable if the average value of the following formula results is taken in the calculation [1] :
- (1) Basal metabolic rate% = (pulse rate + pulse pressure difference)-111 (Gale method) [1]
- (2) Basal metabolic rate% = 0.75 × (pulse rate + pulse pressure difference × 0.74)-72 (Reed method) [1]
- (3) Basal metabolic rate% = 1.28 × (pulse rate + pulse pressure difference)-116 (Kosa method) [1]
Clinical significance of basal metabolic rate
| age) | 11 ~ 15 | 16 ~ 17 | 18 ~ 19 | 20 ~ 30 | 31 ~ 40 | 41 ~ 50 | 51 or more |
|---|---|---|---|---|---|---|---|
| 195.5 | 193.4 | 166.2 | 157.8 | 158.7 | 154.0 | 149.0 |
| female | 172.5 | 181.7 | 154.0 | 146.5 | 146.9 | 142.4 | 138.6 |
- As shown in Table 1 [4] , basal metabolic rate varies with age and gender. However, in normal people of the same sex, weight and age group, the basal metabolic rate is very close. Among them, about 90% of the people have a metabolic rate that does not differ from the average by more than 15%. Therefore, clinically, this percentage value is used as the limit of the normal value. Exceeding this limit is considered as a basal metabolic abnormality. For example, in patients with hyperthyroidism, the basal metabolic rate may be 20 to 80% higher than normal; while patients with hypothyroidism are 20 to 40% lower than normal.
- The measurement of basal metabolic rate is a simple and effective method for clinical diagnosis of thyroid disease. Others, such as adrenal cortex and anterior pituitary hormone secretion, can also be manifested as reduced basal metabolic rate. As body temperature rises, basal metabolic rate also increases. Normally, for every 1 ° C increase in body temperature, the basal metabolic rate increases by 13%. When people are chronically hungry or undernourished, their basal metabolism decreases. In addition, the determination of basal metabolic rate and energy metabolic rate under different activity intensities is also the basis for rationally formulating nutritional standards and arranging people's diets [5] .
Factors Affecting Basal Metabolic Rate
Basal metabolic rate body surface area
- The body's total basal metabolism is obviously different with different body sizes.
- Figure 1 Normal basal metabolic rate by sex and age
- A = 0.00659H + 0.0126W-0.1603 [5]
- A: Body surface area (square of m) [5]
- H: Height (cm) [5]
- W: weight (kg) [5]
Basal metabolic rate age sex
- The basal metabolic rate of women is slightly lower than that of men. During infancy, the growth of body tissues is strong, and the basal metabolic rate is the highest. Later, it gradually decreases with age (see Figure 1), and the basal metabolic rate of pregnant women is relatively high [6] .
Basal Metabolic Rate Ambient Temperature and Climate
- Ambient temperature has a significant impact on basal metabolism. In a comfortable environment (20-25 ° C), metabolism is lowest; in low and high temperature environments, metabolism is elevated. Too low ambient temperature may cause varying degrees of tremor to affect elevated metabolism; when the ambient temperature is high, sweating is required due to heat dissipation, and breathing and heart rate are accelerated. As a result, the metabolism is increased [6] .
Basal Metabolic Rate Nutrition and Functional Status
- During periods of severe hunger and chronic malnutrition, the basal metabolic rate of the body can be reduced by up to 50%. Diseases and infections can increase basal metabolic rates. Hyperthyroidism and elevated adrenaline can increase basal metabolic rate [6] .
Basal metabolic rate thyroid function
- Thyroxine can increase the rate of all biochemical reactions in all cells. Therefore, an increase in thyroid hormone can cause an increase in basal metabolic rate. The measurement of basal metabolic rate is one of the important diagnostic indicators of clinical hyperthyroidism. In patients with hyperthyroidism, the basal metabolic rate can increase by 40 to 80% from the normal average, and in patients with hypothyroidism, it can be 40 to 50% lower than the normal value. [6]
Other factors of basal metabolic rate
- Factors that affect the basal metabolic rate of the human body include drugs and sympathetic nerve activity, such as nicotine and caffeine, which can also increase the basal metabolic rate [6] [6] .