Basal metabolic rate

The basal metabolic rate , and resting energy requirements , often resting energy expenditure , resting energy expenditure , basic metabolic rate , basic needs or basal metabolic rate is the energy per unit of time, which an organism to maintain homeostasis required.

Basic functions in this context include breathing, blood circulation, thermoregulation and digestion. Energy that is required for physical activity or heavy sweating is not included in the basal metabolic rate. From a physical point of view, the basal metabolic rate is an output whose SI unit is the watt . In practice, however, instead of the legal unit of energy, the joule , the outdated unit of heat, the calorie (this usually means kilocalorie ), is used and the basal metabolic rate - since it is always over a whole day, i.e. 24 Hours refers - accordingly stated in kilocalories per 24 hours (kcal / 24 h) (whereby the indication “/ 24 h” is often omitted). In the English-language specialist literature, the term resting energy expenditure (REE) is used for the resting energy requirement .

The scientific literature increasingly formulates the basal metabolic rate with the SI unit megajoules per day (MJ / d) (example: Journal of Nutrition). The food information regulation also stipulates the specification of the physiological calorific value in the unit kJ / 100 g in the movement of goods in the EU , so that the energy balance of food in the International System of Units (SI) can also be calculated using the mass balance . For the conversion between kilojoules and kilocalories there are - depending on the definition of the standard conditions - slightly different factors. The 9th General Conference on Weights and Measures established the following conversion factor in 1948:

${\displaystyle 1\;\mathrm {kcal} =4{,}18684\;\mathrm {kJ} }$and . ${\displaystyle 1\;\mathrm {kJ} =0{,}2388\;\mathrm {kcal} }$

Factors that influence the basal metabolic rate include: a .: Age , gender , body weight , body size , muscle mass , thermal insulation through clothing as well as the 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, which arithmetically accounts for the maintenance of homeostasis during physical rest. These include thermoregulation , the mechanical work of the heart and lungs, the growth of the organism, the membrane potential , the substrate metabolism and the brain's energy requirements. In humans, the resting energy requirement accounts for around 50 to 75% of the total energy requirement (Total Energy Expenditure, TEE). In addition, there are - individually different - 15 to 40% activity-dependent energy requirements and up to 10% food- induced thermogenesis (NIT). The activity-dependent energy requirement varies depending on 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 metabolism of the supplied nutrients.

Determination and calculation of the idle energy requirement

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

The resting energy requirement of patients

The total energy requirement of bedridden patients is usually only slightly, in the range from 0 to 7%, above the resting energy requirement.

The additional energy requirement above the normal resting energy requirement is, however, strongly dependent on the disease. After surgery, for example, the increase is around 28%, in the case of an injury or sepsis by 26%, in cancer by 18% and in respiratory diseases by 9%.

Measurement

Indirect calorimetry in the laboratory with a canopy hood (dilution method)

Using calorimetry methods , the basal metabolic rate can be measured directly via the amount of heat given off or indirectly via the oxygen consumption, which is too time-consuming for everyday life outside of scientific research, for example in hospitals .

Direct calorimetry was developed by Antoine Laurent de Lavoisier in the 18th century , but is now only of historical importance. Instead, in today's medical practice, the subject's respiratory flow is measured with spirometers and from this the volume of the breath , the oxygen consumption and, ultimately, the basal metabolic rate itself is determined.

Calculation using approximation formulas

Harris-Benedict formula

Basal metabolic rate in kCal per day for men according to Harris-Benedict and BMI formulas, based on age and weight for a BMI of 21.5

Basal metabolic rate in kCal per day for women according to Harris-Benedict and BMI formulas, based on age and weight for a BMI of 21.5

In 1918, JA Harris and FG Benedict published the Harris-Benedict formula named after them, which includes body mass , height and age as factors influencing the basal metabolic rate. ${\displaystyle m}$ ${\displaystyle l}$ ${\displaystyle t}$

The formula still represents a good approximation of the measured basal metabolic rate that is generally accepted in nutritional medicine . For men it is: ${\displaystyle G}$

${\displaystyle G_{\mathrm {m} }(m,l,t)=(66{,}5+13{,}7{\tfrac {1}{\mathrm {kg} }}\,m+5{,}0{\tfrac {1}{\mathrm {cm} }}\,l-6{,}8{\tfrac {1}{\mathrm {a} }}\,t){\tfrac {\mathrm {kcal} }{\mathrm {24\,h} }}\,,}$

and for women

${\displaystyle G_{\mathrm {w} }(m,l,t)=(655+9{,}6{\tfrac {1}{\mathrm {kg} }}\,m+1{,}8{\tfrac {1}{\mathrm {cm} }}\,l-4{,}7{\tfrac {1}{\mathrm {a} }}\,t){\tfrac {\mathrm {kcal} }{\mathrm {24\,h} }}\,.}$

In legal units that lead to the result in the SI unit kJ per day, the formulas for men are:

${\displaystyle G_{\mathrm {m} }(m,l,t)=(278{,}42+57{,}36{\tfrac {1}{\mathrm {kg} }}\,m+20{,}93{\tfrac {1}{\mathrm {cm} }}\,l-28{,}47{\tfrac {1}{\mathrm {a} }}\,t){\tfrac {\mathrm {kJ} }{\mathrm {24\,h} }}\,,}$

and for women:

${\displaystyle G_{\mathrm {w} }(m,l,t)=(2.742{,}35+40{,}19{\tfrac {1}{\mathrm {kg} }}\,m+7{,}54{\tfrac {1}{\mathrm {cm} }}\,l-19{,}68{\tfrac {1}{\mathrm {a} }}\,t){\tfrac {\mathrm {kJ} }{\mathrm {24\,h} }}\,.}$

The noticeable difference in the first summand by almost a power of ten expresses that the basal metabolic rate in men is more determined by body stature and the muscle mass that is dependent on it.

Broca index adjustment

Since the basal metabolic rate per kilogram of body weight decreases with increasing body fat percentage , the above should mainly be used from a BMI of 30 kg / m². Formulas a corrected body weight can be used, which is calculated taking into account the normal weight according to Paul Broca as follows: ${\displaystyle m_{\mathrm {korr} }}$ ${\displaystyle m_{\mathrm {norm} }}$

${\displaystyle m_{\mathrm {korr} }=m_{\mathrm {norm} }+{\tfrac {1}{4}}\,(m-m_{\mathrm {norm} })={\tfrac {3}{4}}\,m_{\mathrm {norm} }+{\tfrac {1}{4}}\,m={\tfrac {3}{4}}\,(l-100\,\mathrm {cm} )\,{\tfrac {\mathrm {kg} }{\mathrm {cm} }}+{\tfrac {1}{4}}\,m}$

A simplification results when both formulas are combined. The corrected basal metabolic rate is obtained without having to use a corrected body weight .

The formula is for men

${\displaystyle G_{\mathrm {korr,m} }(m,l,t)=(3{,}4{\tfrac {1}{\mathrm {kg} }}\,m+15{,}3{\tfrac {1}{\mathrm {cm} }}\,l-6{,}8{\tfrac {1}{\mathrm {a} }}\,t-961){\tfrac {\mathrm {kcal} }{\mathrm {24\,h} }}\,,}$

and for women

${\displaystyle G_{\mathrm {korr,w} }(m,l,t)=(2{,}4{\tfrac {1}{\mathrm {kg} }}\,m+9{,}0{\tfrac {1}{\mathrm {cm} }}\,l-4{,}7{\tfrac {1}{\mathrm {a} }}\,t-65){\tfrac {\mathrm {kcal} }{\mathrm {24\,h} }}\,.}$

In legal units that lead to the result in the SI unit kJ per day, the formulas for men are:

${\displaystyle G_{\mathrm {korr,m} }(m,l,t)=(14{,}24{\tfrac {1}{\mathrm {kg} }}\,m+64{,}06{\tfrac {1}{\mathrm {cm} }}\,l-28{,}47{\tfrac {1}{\mathrm {a} }}\,t-4.023{,}55){\tfrac {\mathrm {kJ} }{\mathrm {24\,h} }}\,,}$

and for women

${\displaystyle G_{\mathrm {korr,w} }(m,l,t)=(10{,}05{\tfrac {1}{\mathrm {kg} }}\,m+37{,}68{\tfrac {1}{\mathrm {cm} }}\,l-19{,}68{\tfrac {1}{\mathrm {a} }}\,t-272{,}14){\tfrac {\mathrm {kJ} }{\mathrm {24\,h} }}\,.}$

Except for the calculation of the corrected basal metabolic rate, the normal weight according to Broca plays practically no role anymore and has been replaced by the body mass index and various other physical parameters for assessing overweight and obesity .

Mifflin-St.Jeor formula

Basal metabolic rate in kCal per day for men and women according to Mifflin-St.Jeor and BMI formulas, based on age and weight for a BMI of 21.5

A more recent formula was proposed by Mifflin and St.Jeor in 1990, which should take into account the lifestyle changes of the last 100 years and is on average about 5% more accurate (mass in kg, height in cm, age in years, basal metabolic rate in kcal per day) .

${\displaystyle G(m,l,t)=10{,}0~m+6{,}25~l-5{,}0~t+s}$

with for men and for women. ${\displaystyle s=+5}$ ${\displaystyle s=-161}$

In legal units that lead to the result in kJ per day, the formula is:

${\displaystyle G(m,l,t)=41{,}87~m+26{,}17~l-20{,}93~t+s}$

with for men and for women. ${\displaystyle s=+20{,}93}$ ${\displaystyle s=-674{,}08}$

Simple estimate

Much simplified, but still suitable for everyday use, is the approximate assumption that humans consume 25 kcal per day per kilogram of body weight under the conditions mentioned. The following simplified formula is derived from this:

${\displaystyle G(m)=25{\tfrac {\mathrm {kcal} }{\mathrm {kg\cdot 24\,h} }}\,m}$

Since a day has 24 hours and 100 kJ corresponds to around 24 kcal, an even simpler rule of thumb with a factor of 24 is used in numerous publications. For example, 100 times the weight gives the basal metabolic rate of one day in kilojoules and the weight itself gives the basal metabolic rate per hour in kcal. According to this rule of thumb, the daily basal metabolic rate for a man is calculated as follows:

${\displaystyle G_{\mathrm {m} }(m)=24\,{\tfrac {\mathrm {kcal} }{\mathrm {kg\cdot 24\,h} }}\,m=1\,{\tfrac {\mathrm {kcal} }{\mathrm {kg\cdot h} }}\cdot m=100\,{\tfrac {\mathrm {kJ} }{\mathrm {kg\cdot 24\cdot h} }}\,m}$

Since men are on average slightly taller and have both more muscle mass and less body fat than women in relation to their body weight, a 10% lower basal metabolic rate is generally assumed for women:

${\displaystyle G_{\mathrm {w} }(m)=0{,}9\cdot 24\,{\tfrac {\mathrm {kcal} }{\mathrm {kg\cdot 24\,h} }}\,m=0{,}9\,{\tfrac {\mathrm {kcal} }{\mathrm {kg\cdot h} }}\,m=90\,{\tfrac {\mathrm {kJ} }{\mathrm {kg\cdot 24\cdot h} }}\,m}$

This results in the following values ​​for a person weighing 70 kg:

${\displaystyle G_{\mathrm {m} }(70\,\mathrm {kg} )=1680\,{\tfrac {\mathrm {kcal} }{\mathrm {24\,h} }}=70\,{\tfrac {\mathrm {kcal} }{\mathrm {h} }}=7000\,{\tfrac {\mathrm {kJ} }{\mathrm {24\cdot h} }}=7000\,{\tfrac {\mathrm {kJ} }{\mathrm {86400\cdot s} }}={\tfrac {7000}{86400}}\,{\tfrac {\mathrm {kJ} }{\mathrm {s} }}=81\,\mathrm {W} }$

${\displaystyle G_{\mathrm {w} }(70\,\mathrm {kg} )=1512\,{\tfrac {\mathrm {kcal} }{\mathrm {24\,h} }}=63\,{\tfrac {\mathrm {kcal} }{\mathrm {h} }}=6300\,{\tfrac {\mathrm {kJ} }{\mathrm {24\cdot h} }}=6300\,{\tfrac {\mathrm {kJ} }{\mathrm {86400\,s} }}={\tfrac {6300}{86400}}\,{\tfrac {\mathrm {kJ} }{\mathrm {s} }}=73\,\mathrm {W} }$

Total energy expenditure

With increased physical activity, the energy expenditure also increases. The additional amount of energy converted per day is called the output . The total energy turnover is the sum of the basic and output turnover. It can be estimated by multiplying the previously determined basal metabolic rate by an activity factor (PAL value, English physical activity level ). This is between 1.2 lying down or sitting and up to 2.4 during heavy physical work, e.g. B. in heavy industry or in competitive sports. For office work, on the other hand, you only get an activity factor of 1.3 to 1.6.

In the event of illness, the basal metabolic rate to determine the actual energy requirement is multiplied not only by the activity factor (which is 1.2 for bedridden patients and 1.3 for mobilized patients) but also by a trauma factor, which is determined by the severity of the illness and between 1 , 0 and 1.6.

Basal metabolic rate in humans

The liver and skeletal muscles account for the largest share of the basal metabolic rate in the human body with about 26% each, followed by the brain with 18%, the heart with 9% and the kidneys with 7%. The remaining 14% are accounted for by the other organs.

See also

• Starvation metabolism

Web links

• Interactive energy demand calculation from the University of Hohenheim

Remarks

1. ↑ Guide for Authors. The Journal of Nutrition (JN) , accessed on April 17, 2019 (English, see there specifically under 5.3.8. Units of measure.). doi : 10.1093 / jn / 128.1.2 
2. ↑ JA Levine and CM Kotz: NEAT (non-exercise activity thermogenesis) egocentric and geocentric environmental factors vs. biological regulation. In: Acta Physiol Scand 184, 2005, pp. 309-318. PMID 16026422 (Review)
3. ^ JA Levine: Non-exercise activity thermogenesis (NEAT). In: Best Pract Res Clin Endocrinol Metab 16, 2002, pp. 679-702. PMID 12468415 (Review)
4. ^ Erwin-Josef Speckmann: Physiology. Urban & Fischer Verlag, ISBN 3-437-41318-X , pp. 588-596.
5. ↑ MJ Müller et al.: Estimation and measurement of energy consumption: methods and significance in clinical diagnostics. In: Intensivmed 29, 1992, pp. 411-426.
6. ^ JA Harris and FG Benedict: Publication No 279A biometric study of basal metabolism in man. In: Carnegie Institution of Washington 1919
7. ↑ University of Düsseldorf: Guideline Parenteral Nutrition Chapter 3 - Energy expenditure and energy supply. according to Akt Ernähr Med 32, 2007, pp. 8-12. doi : 10.1055 / s-2006-951862 accessed on September 13, 2016
8. ↑ W. Behrendt et al .: How reliable are short-term measurements of oxygen uptake in polytraumatized and long-term ventilated patients? In: Infusionsther Transfusionsmed 18, 1991, pp. 20-24. PMID 2030048
9. ^ DC Frankenfield et al .: Relationships between resting and total energy expenditure in injured and septic patients. In: Crit Care Med 22, 1994, pp. 1796-1804. PMID 7956284
10. ↑ NA Smyrnios et al .: Accuracy of 30-minute indirect calorimetry studies in predicting 24-hour energy expenditure in mechanically ventilated, critically ill patients. In: JPEN 21, 1997, pp. 168-174. PMID 9168370
11. ↑ DL Swinamer include: Twenty-four hour energy expenditure in critically ill patients. In: Crit Care Med 15, 1987, pp. 637-643. PMID 3595152
12. ^ C. Weissman, M. Kemper, DH Elwyn, J. Askanazi, AI Hyman, JM Kinney: The energy expenditure of the mechanically ventilated critically ill patient. An analysis. In: Chest. Volume 89, Number 2, February 1986, pp. 254-259, PMID 3943386 .
13. ^ JM Miles: Energy expenditure in hospitalized patients: implications for nutritional support. In: Mayo Clinic Proceedings. Volume 81, Number 6, June 2006, pp. 809-816, doi : 10.4065 / 81.6.809 , PMID 16770981 .
14. ↑ Horst de Marées: Sportphysiologie S. 381ff Cologne 2003. ISBN 3-939390-00-3
15. ^ Harris J, Benedict F: A Biometric Study of Human Basal Metabolism . In: Proc Sci US a . 4, No. 12, 1918, pp. 370-3. doi : 10.1073 / pnas.4.12.370 . PMID 16576330 . PMC 1091498 (free full text).
16. ↑ Mifflin, St Jeor et al: A new predictive equation for resting energy expenditure in healthy individuals . In: American Journal of Clinical Nutrition . 51, No. 2, pp. 241-247. PMID 2305711 .
17. ^ David Frankenfield et al: Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults: A Systematic Review . In: Journal of the American Dietetic Association . 105, No. 5, May 2005, pp. 775-789. doi : 10.1016 / j.jada.2005.02.005 .
18. ^ Robert F. Schmidt , Florian Lang, Manfred Heckmann: Physiologie des Menschen. with pathophysiology . 31st edition. SpringerMedizin Verlag, Heidelberg 2010, ISBN 978-3-642-01650-9 , p. 838 .