Examining Variations of Resting Metabolic Rate of Adults
Purpose. There has not been a recent comprehensive effort to examine existing studies on the resting metabolic rate (RMR) of adults to identify the effect of common population demographic and anthropometric characteristics. Thus, we reviewed the literature on RMR (kcal·kg·h) to determine the relationship of age, sex, and obesity status to RMR as compared with the commonly accepted value for the metabolic equivalent (MET; e.g., 1.0 kcal·kg·h).
Methods. Using several databases, scientific articles published from 1980 to 2011 were identified that measured RMR, and from those, others dating back to 1920 were identified. One hundred and ninety-seven studies were identified, resulting in 397 publication estimates of RMR that could represent a population subgroup. Inverse variance weighting technique was applied to compute means and 95% confidence intervals (CI).
Results. The mean value for RMR was 0.863 kcal·kg·h (95% CI = 0.852–0.874), higher for men than women, decreasing with increasing age, and less in overweight than normal weight adults. Regardless of sex, adults with BMI ≥ 30 kg·m had the lowest RMR (<0.741 kcal·kg·h).
Conclusions. No single value for RMR is appropriate for all adults. Adhering to the nearly universally accepted MET convention may lead to the overestimation of the RMR of approximately 10% for men and almost 15% for women and be as high as 20%–30% for some demographic and anthropometric combinations. These large errors raise questions about the longstanding adherence to the conventional MET value for RMR. Failure to recognize this discrepancy may result in important miscalculations of energy expended from interventions using physical activity for diabetes and other chronic disease prevention efforts.
Resting metabolic rate (RMR), also called resting energy expenditure, is important to understand because it typically accounts for the largest portion of total energy needs. RMR is typically defined as the energy required by the body in a resting condition. The definition can be further refined as the amount of energy expended when the individual is awake, in a postabsorptive, thermoneutral state while having not exercised for typically 12 h. RMR has been measured either in the sitting or supine positions, with a minimum of 15 min of rest, sometimes up to an overnight rest. Resting and basal metabolic rate (BMR) are similar and only differ in that BMR is usually measured in the morning, after an overnight fast, no exercise for the previous 24 h, free from emotional stress, familiar with the apparatus, and the subject completely rested. In general, RMR may be a better indicator of daily energy needs than BMR. Although there have been comparative studies on the influence of sex, age, and obesity status on BMR, which have resulted in prediction equations, there is little comprehensive comparative data on the influence of sex, age, and obesity status on RMR. Studies have shown differences in RMR between men and women, between obese and nonobese adults, and possibly racial/ethnic differences. Furthermore, older adults (>70 yr) have lower RMRs than younger adults by as much as 20%–25%. However, to our knowledge, there has not been an examination of combined effects of sex, age, and obesity status on RMR to approximate group characteristics normally encountered in public health efforts.
The metabolic equivalent (MET) is a common term used by exercise physiologists, epidemiologists, and the medical community to express RMR. In addition, energy demands of various physical activities have been represented by multiples of a MET, made relative to RMR. The concept of a MET has been in use for quite some time, but the exact derivation is not known. The conventional definition of one MET is 3.5 mL oxygen per kilogram body mass per minute (3.5 mL·kg·min) and is assumed to be approximately equal to 1 kcal·kg·h or 4.184 kJ·kg·h. In all three articles by Ainsworth et al., the energy expenditure of a MET is noted to be imprecise and seen only as a means of classifying activities based on the expected intensity of typical activity participation when expressed as a multiple of 1 MET. Work by Byrne et al. suggests that the use of the conventionally defined MET value often reflects an overestimate that does not apply well to all individuals nor to population subgroups. Unfortunately, applying a standard MET value to all individuals has attained widespread acceptance but has been questioned in the past decade by the scientific community.
A perusal of the RMR literature reveals that considerable information on studies of specific population subgroups (e.g., men, women, children, obese, and patient populations) is based primarily on relatively small sample sizes, or studies that were not intended to be population based. Although reviews have been completed, there has not been any comprehensive effort to assemble RMR estimates from existing studies to identify the combined effect of common demographic (sex and age) and obesity status (body mass index) characteristics that apply to groups of individuals encountered in the delivery of public health interventions. Such an effort is important because the convention of applying a single estimate of RMR to an entire population subgroup is likely to misrepresent expected energy costs of physical activity promotion intended to achieve, for example, energy balance among groups of men or women who are overweight or obese. In addition, the issue is relevant to public health efforts that target groups of individuals for the delivery of physical activity programs, to say, older adult, overweight women versus younger, and obese men, in hopes of thwarting the growing diabetes epidemic. Thus, the purposes of this article were to examine the literature on RMR and to determine the extent to which age, sex, and obesity status relate to RMR as compared with the commonly accepted value for a MET.
Abstract and Introduction
Abstract
Purpose. There has not been a recent comprehensive effort to examine existing studies on the resting metabolic rate (RMR) of adults to identify the effect of common population demographic and anthropometric characteristics. Thus, we reviewed the literature on RMR (kcal·kg·h) to determine the relationship of age, sex, and obesity status to RMR as compared with the commonly accepted value for the metabolic equivalent (MET; e.g., 1.0 kcal·kg·h).
Methods. Using several databases, scientific articles published from 1980 to 2011 were identified that measured RMR, and from those, others dating back to 1920 were identified. One hundred and ninety-seven studies were identified, resulting in 397 publication estimates of RMR that could represent a population subgroup. Inverse variance weighting technique was applied to compute means and 95% confidence intervals (CI).
Results. The mean value for RMR was 0.863 kcal·kg·h (95% CI = 0.852–0.874), higher for men than women, decreasing with increasing age, and less in overweight than normal weight adults. Regardless of sex, adults with BMI ≥ 30 kg·m had the lowest RMR (<0.741 kcal·kg·h).
Conclusions. No single value for RMR is appropriate for all adults. Adhering to the nearly universally accepted MET convention may lead to the overestimation of the RMR of approximately 10% for men and almost 15% for women and be as high as 20%–30% for some demographic and anthropometric combinations. These large errors raise questions about the longstanding adherence to the conventional MET value for RMR. Failure to recognize this discrepancy may result in important miscalculations of energy expended from interventions using physical activity for diabetes and other chronic disease prevention efforts.
Introduction
Resting metabolic rate (RMR), also called resting energy expenditure, is important to understand because it typically accounts for the largest portion of total energy needs. RMR is typically defined as the energy required by the body in a resting condition. The definition can be further refined as the amount of energy expended when the individual is awake, in a postabsorptive, thermoneutral state while having not exercised for typically 12 h. RMR has been measured either in the sitting or supine positions, with a minimum of 15 min of rest, sometimes up to an overnight rest. Resting and basal metabolic rate (BMR) are similar and only differ in that BMR is usually measured in the morning, after an overnight fast, no exercise for the previous 24 h, free from emotional stress, familiar with the apparatus, and the subject completely rested. In general, RMR may be a better indicator of daily energy needs than BMR. Although there have been comparative studies on the influence of sex, age, and obesity status on BMR, which have resulted in prediction equations, there is little comprehensive comparative data on the influence of sex, age, and obesity status on RMR. Studies have shown differences in RMR between men and women, between obese and nonobese adults, and possibly racial/ethnic differences. Furthermore, older adults (>70 yr) have lower RMRs than younger adults by as much as 20%–25%. However, to our knowledge, there has not been an examination of combined effects of sex, age, and obesity status on RMR to approximate group characteristics normally encountered in public health efforts.
The metabolic equivalent (MET) is a common term used by exercise physiologists, epidemiologists, and the medical community to express RMR. In addition, energy demands of various physical activities have been represented by multiples of a MET, made relative to RMR. The concept of a MET has been in use for quite some time, but the exact derivation is not known. The conventional definition of one MET is 3.5 mL oxygen per kilogram body mass per minute (3.5 mL·kg·min) and is assumed to be approximately equal to 1 kcal·kg·h or 4.184 kJ·kg·h. In all three articles by Ainsworth et al., the energy expenditure of a MET is noted to be imprecise and seen only as a means of classifying activities based on the expected intensity of typical activity participation when expressed as a multiple of 1 MET. Work by Byrne et al. suggests that the use of the conventionally defined MET value often reflects an overestimate that does not apply well to all individuals nor to population subgroups. Unfortunately, applying a standard MET value to all individuals has attained widespread acceptance but has been questioned in the past decade by the scientific community.
A perusal of the RMR literature reveals that considerable information on studies of specific population subgroups (e.g., men, women, children, obese, and patient populations) is based primarily on relatively small sample sizes, or studies that were not intended to be population based. Although reviews have been completed, there has not been any comprehensive effort to assemble RMR estimates from existing studies to identify the combined effect of common demographic (sex and age) and obesity status (body mass index) characteristics that apply to groups of individuals encountered in the delivery of public health interventions. Such an effort is important because the convention of applying a single estimate of RMR to an entire population subgroup is likely to misrepresent expected energy costs of physical activity promotion intended to achieve, for example, energy balance among groups of men or women who are overweight or obese. In addition, the issue is relevant to public health efforts that target groups of individuals for the delivery of physical activity programs, to say, older adult, overweight women versus younger, and obese men, in hopes of thwarting the growing diabetes epidemic. Thus, the purposes of this article were to examine the literature on RMR and to determine the extent to which age, sex, and obesity status relate to RMR as compared with the commonly accepted value for a MET.
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