Resting metabolic rate

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Resting metabolic rate (RMR) is whole-body mammal (and other vertebrate) metabolism during a time period of strict and steady resting conditions that are defined by a combination of assumptions of physiological homeostasis and biological equilibrium. RMR differs from basal metabolic rate (BMR) because BMR measurements must meet total physiological equilibrium whereas RMR conditions of measurement can be altered and defined by the contextual limitations. Therefore, BMR is measured in the elusive "perfect" steady state, whereas RMR measurement is more accessible and thus, represents most, if not all measurements or estimates of daily energy expenditure. [1]

Contents

Indirect calorimetry is the study or clinical use of the relationship between respirometry and bioenergetics, where the measurement of the rates of oxygen consumption, sometimes carbon dioxide production, and less often urea production is transformed to rates of energy expenditure, expressed as the ratio between i) energy and ii) the time frame of the measurement. For example, following analysis of oxygen consumption of a human subject, if 5.5 kilocalories of energy were estimated during a 5-minute measurement from a rested individual, then the resting metabolic rate equals = 1.1 kcal/min rate. Unlike some related measurements (e.g. METs), RMR itself is not referenced to body mass and has no bearing on the energy density of the metabolism.

A comprehensive treatment of confounding factors on BMR measurements is demonstrated as early as 1922 in Massachusetts by Engineering Professor Frank B Sanborn, wherein descriptions of the effects of food, posture, sleep, muscular activity, and emotion provide criteria for separating BMR from RMR. [2] [3] [4]

Indirect calorimetry

Pre-computer technologies

In the 1780s for the French Academy of Sciences, Lavoisier, Laplace, and Seguin investigated and published relationships between direct calorimetry and respiratory gas exchanges from mammalian subjects. 100 years later in the 19th century for the Connecticut-based Wesleyan University, Professors Atwater and Rosa provided ample evidence of nitrogen, carbon dioxide, and oxygen transport during the metabolism of amino acids, glucose, and fatty acids in human subjects, further establishing the value of indirect calorimetry in determining bioenergetics of free-living humans. [5] [6] The work of Atwater and Rosa also made it possible to calculate the caloric values of foods, which eventually became the criteria adopted by the USDA to create the food calorie library. [7]

In the early 20th century at Oxford University, physiology researcher Claude Gordon Douglas developed an inexpensive and mobile method of collecting exhaled breath (partly in preparation for experiments to be conducted on Pike's Peak, Colorado). In this method, the subject exhales into a nearly impermeable and large volume collection bag over a recorded period of time. The entire volume is measured, the oxygen and carbon dioxide content are analyzed, and the differences from inspired "ambient" air are calculated to determine the rates of oxygen uptake and carbon dioxide output. [8]

To estimate energy expenditure from the exhaled gases, several algorithms were developed. One of the most widely used was developed in 1949 at University of Glasgow by research physiologist J. B. de V. Weir. His abbreviated equation for estimating metabolic rate was written with rates of gas exchange being volume/time, excluded urinary nitrogen, and allowed for the inclusion of a time conversion factor of 1.44 to extrapolate to 24-hour energy expenditure from 'kcal per minute" to "kcal per day." Weir used the Douglas Bag method in his experiments, and in support of neglecting the effect of protein metabolism under normal physiological conditions and eating patterns of ~12.5% protein calories, he wrote:

"...In fact if the percentage of protein calories [consumed] lies between 10 and 14 the maximum error in using [the equation] is less than 1 in 500." [9]
An overview of how oxygen and carbon dioxide relate to human energy expenditure Resting Metabolic Rate.png
An overview of how oxygen and carbon dioxide relate to human energy expenditure

Computer-aided RMR measurements

In the early 1970s, computer technology enabled on-site data processing, some real-time analysis, and even graphical displays of metabolic variables, such as O2, CO2, and air-flow, thereby encouraging academic institutions to test accuracy and precision in new ways. [10] [11] A few years later in the decade, battery-operated systems made debuts. For example, a demonstration of the mobile system with digital display of both cumulative and past-minute oxygen consumption was presented in 1977 at the Proceedings of the Physiological Society. [12] As manufacturing and computing costs dropped over the next few decades, various universal calibration methods for preparing and comparing various models in the 1990s brought attention to short-comings or advantages of various designs. [13] In addition to lower costs, the metabolic variable CO2 was often ignored, promoting instead a focus on oxygen-consumption models of weight management and exercise training. In the new millennium, smaller "desktop-sized" indirect calorimeters were being distributed with dedicated personal computers and printers, and running modern windows-based software. [14]

Use

RMR measurements are recommended when estimating total daily energy expenditure (TEE). Since BMR measures are restricted to the narrow time frame (and strict conditions) upon waking, the looser-conditions RMR measure is more typically conducted. In the review organized by the USDA, [15] most publications documented specific conditions of resting measurements, including time from latest food intake or physical activities; this comprehensive review estimated RMR is 10 – 20% higher than BMR due to thermic effect of feeding and residual burn from activities that occur throughout the day.

Relationship between resting metabolic rate and energy expenditure

Thermochemistry aside, the rate of metabolism and an amount of energy expenditures can be mistakenly interchanged, for example, when describing RMR and REE.

Clinical guidelines for conditions of resting measurements

The Academy of Nutrition and Dietetics (AND) provides clinical guidance for preparing a subject for RMR measures, [16] in order to mitigate possible confounding factors from feeding, stressful physical activities, or exposure to stimulants such as caffeine or nicotine:

In preparation, a subject should be fasting for 7 hrs or greater, and mindful to avoid stimulants and stressors, such as caffeine, nicotine, and hard physical activities such as purposeful exercises.

For 30 minutes before conducting the measurement, a subject should be laying supine without physical movements, no reading nor listening to music. The ambiance should reduce stimulation by maintaining constant quiet, low lighting, and steady temperature. These conditions continue during the measurement stage.

Further, the correct use of a well-maintained indirect calorimeter includes achieving a natural and steady breathing pattern in order to reveal oxygen consumption and carbon dioxide production rates under a reproducible resting condition. Indirect calorimetry is considered the gold-standard method to measure RMR. [17] Indirect calorimeters are usually found in laboratory and clinical settings, but technological advancements are bringing RMR measurement to free-living conditions.

Use of REE in weight management

Long-term weight management is directly proportional to calories absorbed from feeding; nevertheless, myriad non-caloric factors also play biologically significant roles (not covered here) in estimating energy intake. In counting energy expenditure, the use of a resting measurement (RMR) is the most accurate method for estimating the major portion of Total daily energy expenditure (TEE), thereby giving the closest approximations when planning & following a Calorie Intake Plan. Thus, estimation of REE by indirect calorimetry is strongly recommended for accomplishing long-term weight management, a conclusion reached and maintained due to ongoing observational research by well-respected institutions such as the USDA, AND (previously ADA), ACSM, and internationally by the WHO.

Common correlates to metabolic rate and 24-hr energy expenditure

Energy expenditure is correlated to a number of factors, listed in alphabetical order.

Work on non-human species

RMR is regularly used in ecology to study the response of individuals to changes in environmental conditions.

Parasites by definition have a negative impact on their hosts and it is thus expected that there might be effects on host RMR. Varying effects of parasite infection on host RMR have been found. Most studies indicate an increase in RMR with parasite infection, but others show no effect, or even a decrease in RMR. It is still unclear why such variation in the direction of change in RMR with parasite infection is seen. [19]

Related Research Articles

A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excreted by cells to create non-cellular structures, such as hair, scales, feathers, or exoskeletons. Some nutrients can be metabolically converted to smaller molecules in the process of releasing energy, such as for carbohydrates, lipids, proteins, and fermentation products, leading to end-products of water and carbon dioxide. All organisms require water. Essential nutrients for animals are the energy sources, some of the amino acids that are combined to create proteins, a subset of fatty acids, vitamins and certain minerals. Plants require more diverse minerals absorbed through roots, plus carbon dioxide and oxygen absorbed through leaves. Fungi live on dead or living organic matter and meet nutrient needs from their host.

Food energy is chemical energy that animals derive from their food to sustain their metabolism, including their muscular activity.

<span class="mw-page-title-main">Exercise physiology</span>

Exercise physiology is the physiology of physical exercise. It is one of the allied health professions, and involves the study of the acute responses and chronic adaptations to exercise. Exercise physiologists are the highest qualified exercise professionals and utilise education, lifestyle intervention and specific forms of exercise to rehabilitate and manage acute and chronic injuries and conditions.

Basal metabolic rate (BMR) is the rate of energy expenditure per unit time by endothermic animals at rest. It is reported in energy units per unit time ranging from watt (joule/second) to ml O2/min or joule per hour per kg body mass J/(h·kg). Proper measurement requires a strict set of criteria to be met. These criteria include being in a physically and psychologically undisturbed state and being in a thermally neutral environment while in the post-absorptive state (i.e., not actively digesting food). In bradymetabolic animals, such as fish and reptiles, the equivalent term standard metabolic rate (SMR) applies. It follows the same criteria as BMR, but requires the documentation of the temperature at which the metabolic rate was measured. This makes BMR a variant of standard metabolic rate measurement that excludes the temperature data, a practice that has led to problems in defining "standard" rates of metabolism for many mammals.

<span class="mw-page-title-main">Anaerobic exercise</span> Physical exercise intense enough to cause lactate formation

Anaerobic exercise is a type of exercise that breaks down glucose in the body without using oxygen; anaerobic means "without oxygen". In practical terms, this means that anaerobic exercise is more intense, but shorter in duration than aerobic exercise.

<span class="mw-page-title-main">Exercise intensity</span>

Exercise intensity refers to how much energy is expended when exercising. Perceived intensity varies with each person. It has been found that intensity has an effect on what fuel the body uses and what kind of adaptations the body makes after exercise. Intensity is the amount of physical power that the body uses when performing an activity. For example, exercise intensity defines how hard the body has to work to walk a mile in 20 minutes.

<span class="mw-page-title-main">Excess post-exercise oxygen consumption</span> Increased rate of oxygen intake following strenuous activity

Excess post-exercise oxygen consumption is a measurably increased rate of oxygen intake following strenuous activity. In historical contexts the term "oxygen debt" was popularized to explain or perhaps attempt to quantify anaerobic energy expenditure, particularly as regards lactic acid/lactate metabolism; in fact, the term "oxygen debt" is still widely used to this day. However, direct and indirect calorimeter experiments have definitively disproven any association of lactate metabolism as causal to an elevated oxygen uptake.

The metabolic equivalent of task (MET) is the objective measure of the ratio of the rate at which a person expends energy, relative to the mass of that person, while performing some specific physical activity compared to a reference, currently set by convention at an absolute 3.5 mL of oxygen per kg per minute, which is the energy expended when sitting quietly by a reference individual, chosen to be roughly representative of the general population, and thereby suited to epidemiological surveys. A Compendium of Physical Activities is available online, which provides MET values for hundreds of activities.

The respiratory quotient is a dimensionless number used in calculations of basal metabolic rate (BMR) when estimated from carbon dioxide production. It is calculated from the ratio of carbon dioxide produced by the body to oxygen consumed by the body. Such measurements, like measurements of oxygen uptake, are forms of indirect calorimetry. It is measured using a respirometer. The respiratory quotient value indicates which macronutrients are being metabolized, as different energy pathways are used for fats, carbohydrates, and proteins. If metabolism consists solely of lipids, the respiratory quotient is approximately 0.7, for proteins it is approximately 0.8, and for carbohydrates it is 1.0. Most of the time, however, energy consumption is composed of both fats and carbohydrates. The approximate respiratory quotient of a mixed diet is 0.8. Some of the other factors that may affect the respiratory quotient are energy balance, circulating insulin, and insulin sensitivity.

Doubly labeled water is water in which both the hydrogen and the oxygen have been partly or completely replaced with an uncommon isotope of these elements for tracing purposes.

Respirometry is a general term that encompasses a number of techniques for obtaining estimates of the rates of metabolism of vertebrates, invertebrates, plants, tissues, cells, or microorganisms via an indirect measure of heat production (calorimetry).

An energy budget is a balance sheet of energy income against expenditure. It is studied in the field of Energetics which deals with the study of energy transfer and transformation from one form to another. Calorie is the basic unit of measurement. An organism in a laboratory experiment is an open thermodynamic system, exchanging energy with its surroundings in three ways - heat, work and the potential energy of biochemical compounds.

The respiratory exchange ratio (RER) is the ratio between the metabolic production of carbon dioxide (CO2) and the uptake of oxygen (O2).

Running economy (RE) a complex, multifactorial concept that represents the sum of metabolic, cardiorespiratory, biomechanical and neuromuscular efficiency during running. Oxygen consumption (VO2) is the most commonly used method for measuring running economy, as the exchange of gases in the body, specifically oxygen and carbon dioxide, closely reflects energy metabolism. Those who are able to consume less oxygen while running at a given velocity are said to have a better running economy. However, straightforward oxygen usage does not account for whether the body is metabolising lipids or carbohydrates, which produce different amounts of energy per unit of oxygen; as such, accurate measurements of running economy must use O2 and CO2 data to estimate the calorific content of the substrate that the oxygen is being used to respire.

The Harris–Benedict equation is a method used to estimate an individual's basal metabolic rate (BMR).

<span class="mw-page-title-main">Weight management</span> Techniques for maintaining body weight

Weight management refers to behaviors, techniques, and physiological processes that contribute to a person's ability to attain and maintain a healthy weight. Most weight management techniques encompass long-term lifestyle strategies that promote healthy eating and daily physical activity. Moreover, weight management involves developing meaningful ways to track weight over time and to identify ideal body weights for different individuals.

A calorie deficit is any shortage in the number of calories consumed relative to the number of calories needed for maintenance of current body weight.

<span class="mw-page-title-main">Indirect calorimetry</span> Measurement of the heat of living organisms through indirect means

Indirect calorimetry calculates heat that living organisms produce by measuring either their production of carbon dioxide and nitrogen waste, or from their consumption of oxygen. Indirect calorimetry estimates the type and rate of substrate utilization and energy metabolism in vivo starting from gas exchange measurements. This technique provides unique information, is noninvasive, and can be advantageously combined with other experimental methods to investigate numerous aspects of nutrient assimilation, thermogenesis, the energetics of physical exercise, and the pathogenesis of metabolic diseases.

The Weir formula is a formula used in indirect calorimetry, relating metabolic rate to oxygen consumption and carbon dioxide production. According to original source, it says:

Paul Deurenberg is a Dutch retired academic, nutritional biochemist and consultant. He was a former associate professor in the Department of Human Nutrition at Wageningen University (WU), and is most known for his research expertise in the areas of energy metabolism, food consumption, and body composition studies.

References

  1. ↑ Ravussin, E.; Burnand, B.; Schutz, Y.; Jéquier, E. (March 1, 1982). "Twenty-four-hour energy expenditure and resting metabolic rate in obese, moderately obese, and control subjects". The American Journal of Clinical Nutrition. 35 (3): 566–573. doi: 10.1093/ajcn/35.3.566 . ISSN   0002-9165. PMID   6801963.
  2. ↑ Sanborn M.S., Frank B (1922). Basal metabolism: its determination and application. p. 20. Retrieved 21 March 2016.
  3. ↑ McNab, B. K. 1997. On the Utility of Uniformity in the Definition of Basal Rate of Metabolism. Physiol. Zool. Vol.70; 718–720.
  4. ↑ Speakman, J.R., Krol, E., Johnson, M.S. 2004. The Functional Significance of Individual Variation in Basal Metabolic Rate. Phys. Biochem. Zool. Vol. 77(6):900–915.
  5. ↑ Report of preliminary investigations on the metabolism of nitrogen and carbon in the human organism, with a respiration calorimeter of special construction. Washington : Govt. Print. Off. 1897. Retrieved 2016-03-07– via The Internet Archive.
  6. ↑ Description of a New Respiration Calorimeter and Experiments on the Conservation of Energy in the Human Body. Washington : Govt. print. off. 1899. Retrieved 2016-03-07– via The Internet Archive.
  7. ↑ Why Calories Count . Retrieved 2016-03-03.{{cite book}}: |website= ignored (help)
  8. ↑ Cunningham, D. J. C. (1964-11-01). "Claude Gordon Douglas. 1882-1963". Biographical Memoirs of Fellows of the Royal Society. 10: 51–74. doi:10.1098/rsbm.1964.0004.
  9. ↑ Weir, J. B. de V. (1949). "New methods for calculating metabolic rate with special reference to protein metabolism". The Journal of Physiology. 109 (1–2): 1–9. doi:10.1113/jphysiol.1949.sp004363. PMC   1392602 . PMID   15394301.
  10. ↑ Beaver, WL; Wasserman, K; Whipp, BJ (1973). "On-line computer analysis and breath-by-breath graphical display of exercise function tests". Journal of Applied Physiology. 34 (1): 128–132. doi:10.1152/jappl.1973.34.1.128. PMID   4697371.
  11. ↑ Wilmore, JH; Davis, JA; Norton, AC (1976). "An automated system for assessing metabolic and respiratory function during exercise". Journal of Applied Physiology. 40 (4): 619–624. doi:10.1152/jappl.1976.40.4.619. PMID   931884.
  12. ↑ Humphrey, SJE; Wolff, HS (1977). "The Oxylog". Journal of Physiology. 267: 12. doi:10.1113/jphysiol.1977.sp011841.
  13. ↑ Huszczuk, A; Whipp, BJ; Wasserman, K (1990). "A respiratory gas exchange simulator for routine calibration in metabolic studies" (PDF). European Respiratory Journal. 3 (4): 465–468. PMID   2114308 . Retrieved 2016-03-07.
  14. ↑ "Angeion 2005 Annual Report -- page 7 -- Narrative Description of Business -- General" (PDF). MGC Diagnostics Company. MGC Diagnostics. Retrieved 2016-03-07.
  15. ↑ "Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients) (2005)". USDA. National Academy of Sciences, Institute of Medicine, Food and Nutrition Board. Archived from the original on 10 March 2016. Retrieved 21 March 2016.
  16. ↑ Raynor, Hollie; Champagne, Catherine (2016). "Position of the Academy of Nutrition and Dietetics: Interventions for the Treatment of Overweight and Obesity in Adults". Journal of the Academy of Nutrition and Dietetics. 116 (1): 129–47. doi:10.1016/j.jand.2015.10.031. PMID   26718656 . Retrieved 21 March 2016.
  17. ↑ Haugen, Heather A.; Chan, Lingtak-Neander; Li, Fanny (2007-08-01). "Indirect calorimetry: a practical guide for clinicians". Nutrition in Clinical Practice. 22 (4): 377–388. doi:10.1177/0115426507022004377. ISSN   0884-5336. PMID   17644692.
  18. ↑ Manore, Melinda; Meyer, Nanna; Thompson, Janice (2009). Sport Nutrition for Health and Performance (2 ed.). United States of America: Human Kinetics. ISBN   9780736052955 . Retrieved 30 October 2019.
  19. ↑ Robar, Nicholas; Murray, Dennis L.; Burness, Gary (2011). "Effects of parasites on host energy expenditure: the resting metabolic rate stalemate". Canadian Journal of Zoology. 89 (11): 1146–1155. doi:10.1139/z11-084.
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