EAL

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

The objectives of this study were to

Collect resting metabolic rate (RMR) in a group of nonobese and obese subjects
Four calculation standards were used to predict RMR

Harris Benedict
Harris Benedict using adjusted body weight in obese subjects
Owen
Mifflin.

Main outcome was percentage of subjects whose calculated RMR fell outside a ±10% limit from measured values.

Definitions

Accuracy for predicted equations: Predicted RMR within ±10% of measured RMR.
Obesity: BMI=30 kg/m²
Morbid obesity: BMI=40 kg/m².

Inclusion Criteria:

Adults—age minimum 18 y
Healthy
Non-hospitalized
Volunteers
Able to give consent
Nonobese and obese individuals.

Exclusion Criteria:

Younger individuals
Inability to ambulate
Steroid use
Known diabetes mellitus (because of fasting state required prior to IC) or thyroid disease
No exclusions on basis of gender or race.

Description of Study Protocol:

Same for all subjects

Anthropometrics: Height and weight measured using standardized protocol
Clinical: None described
Resting metabolic rate (RMR): Measured by indirect calorimetry (IC)
IC type: Open-circuit with gas collection via a rigid plastic canopy
Rest before measurement: Amount of time not described
Measurement length: 30 minutes with first 5 minutes of data discarded
Fasting prior to measurement: 12-15 hour fast overnight (away from research center)
Exercise restriction prior to measurement: Subjects abstained from physical exercise during the 12-15 hour fasting period
Room temperature: Ambient controlled by subject (light blankets offered)
Number of measurements: One 30 minute
Coefficient of variation: =10%.
Calibration of IC machine: Stated calibrated
Training of measurer: Not described
Subject given prior explanation of protocol and IC to minimize anxiety: Not discussed
Dietary Measurements: Not done.

Data Collection Summary:

Body mass index (BMI) calculated as kg/m²
Predicted equations used for study:

Harris Benedict (1917) (5% of subjects had BMI =30 kg/m²
Variation of Harris Benedict where all subjects with BMI =30 kg/m²had an adjusted weight substituted into the equation: Adjusted wt (kg)=( (body wt - ideal wt)x0.25) + ideal wt
Owen (1986) with subjects of varying weights; 30% had BMI =30 kg/m²
Mifflin (1990); 47% of subjects were obese with maximum BMI 42 kg/m².

[Note: Owen and Mifflin do not use weight adjustments for obesity.]

Ideal body weight was determined from body height and calculated with the Hamwi equation.

Description of Actual Data Sample:

134 (54 male, 76 female) non-hospitalized adult volunteers;
Subjects recruited by flyers posted in hospital and medical school , some were referred from a weight management clinic
Some from a surgery clinic evaluating morbidly obese individuals for gastric bypass surgery.
Sample was 98% Caucasian (5% from Australia or Europe in US for at least one year to study).

Grouped by degree of obesity

Range of BMI: 18.8-96.8 kg/m²
Obese group divided into obese and morbid obese groups (see definitions under measurements)
Description of 3 groups (nonobese, obese and morbid obese).

Nonobese (n=83)

Ht (cm)=range 146-192
Wt (kg)=range 39-103
BMI (kg/m²)=range 15.9-29.6
RMR (kcal/d)=range 990-2090
Men
Mean age: 41±2.9 (range 20-78) SEM
Women
Mean age: 38±2.2 (range: 22-74) SEM.

Obese (N=20)

Ht (cm)=range 154-189
Wt (kg)=range 77-133
BMI (kg/m²)=range 30.5-39.9
RMR (kcal/d)=range 1214-2654
Men
Mean age: 39±4 (range 18-62) SEM
Women
Mean age: 44±4 (range 26-69) SEM

Morbid Obese (N=27)

Ht (cm)=range 145-192
Wt (kg)=range 109-330
BMI (kg/m²)=range 40.1-96.8
RMR (kcal/d)=range 1679-4533
Men
Mean age: 41±3 (range 28-57) SEM
Women
Mean age: 37±2 (range 25-52) SEM.

No withdrawals discussed.

Summary of Results:

Statistics

Each equation was compared to measured RMR by computing the absolute percent difference between calculated and measured values as a percent of measured RMR. Percent difference was presented in absolute terms to eliminate the mathematical tendency for negative variation to offset positive variation, thus keeping the mean near zero.
Statistical significance was set at P<0.05.

For Equations

Mean percent difference between calculated and measured RMR with inaccurate predictions of RMR (i.e., calculated >10% of measured). Mean values ±SEM shown.

Harris Benedict
Not obese: 13.3±0.8
All obese: 20.0±1.9 (p <0.05 not obese of same equation, vs. Mifflin of the same group)
Obese: 16.4±1.4
Morbid obese: 26.2±1.6 (p <0.05 not obese of the same equation, vs. Mifflin of the same group, vs. BMI 30-40 of the same equation, vs. Owen of the same group).

Harris Benedict (adj. weight)
All obese: 25.0±1.3 (p <0.05 vs. Mifflin of the same group)
Obese: 19.5±2.1
Morbid obese: 26.7±1.2 (p <0.05 vs. Mifflin of the same group, vs. BMI 30-40 of the same equation, vs. Owen of the same group.

Owen
Not obese: 15.4±1.1
All obese: 16.3±1.0
Obese: 21.4±2.4
Morbid obese: 16.0±1.3.

Mifflin
Not obese: 13.7±1.0
All obese: 13.6±0.8
Obese: 17.4±1.6
Morbid obese: 13.0±1.3.

Major Results

The groups were evenly matched for height and age.
BMI was normally distributed within the obesity groupings, but skewed toward a high BMI in the overall sample.
BMI was greater than 30 kg/m² in 36% of subjects with 57% of those having BMI in excess of 40 kg/m²
56% of subjects had sedentary lifestyles; the remainder undertook physical activity for recreation rather than occupational reasons.
Subjects whose predicted RMR was inaccurately predicted did not differ in height or age from those whose RMR was accurately predicted.
For the sample as a whole, the Mifflin equation was accurate more often (78%) than either the Harris Benedict (67%, P=0.05) or Owen equations (65%, P=0.02).
Harris Benedict was significantly less accurate than Mifflin in nonobese subjects, while Owen was significantly less accurate than Mifflin in all obese subjects grouped together, with the errors concentrated in the morbid obese group.
When errors occurred, they tended to be overestimates for the Harris Benedict equation (using actual body weight) and underestimates for all other equations.
Focusing on morbidly obese individuals in this study, use of Harris Benedict equation indicated a 12% overestimation using actual body weight and 22% underestimation using adjusted body weight (compared to 15% and 27%, respectively found in one validation study).
In the nonobese individuals in this study, the Harris Benedict and especially Mifflin equations were more accurate (accuracy rate 69% and 82%, respectively), while the Owen equation had an accuracy rate of 73% when compared to 55%, 52%, and 90%, respectively in one study of 67 nonobese men and women.
The results suggest that the Mifflin equation is accurate more often than the Harris Benedict or Owen equations in both obese and nonobese people, and that the Owen and Harris Benedict equations are similar to one another in accuracy.
Although error was more likely in obese than nonobese people for all equations, there were no clinically applicable markers to identify those people whose predicted RMR should be questioned.
Using adjusted body weight in the Harris Benedict equation caused underestimation of RMR in obesity, with the magnitude of the error increasing as BMI increased. Thus, the use of adjusted body weight is not a reasonable maneuver in the clinical setting.
RMR was predicted inaccurately by the Owen equation in 92% of women with morbid obesity, suggesting this is the threshold above which this equation should not be used.
The Mifflin equation does not appear to have a BMI threshold above which the equation fails to work with a large segment of people, though the accuracy rate in obese individuals is lower than in nonobese individuals.
In morbid obese individuals, the Harris Benedict equation tended to overestimate, while errors in the Owen and Mifflin equations tended to be underestimates.

Author Conclusion:

“Of the equations tested, the Mifflin equation provided an accurate estimate of actual RMR in the largest percentage of nonobese and obese people, with a low rate of overestimation.”
“Among morbidly obese people whose RMR was not accurately predicted, the magnitude of error was smaller for the Mifflin equation than for the other equations.”
Thus, the Mifflin equation deserves consideration as the standard for calculation of RMR in obese and nonobese individuals.
“The clinician can expect disagreement between measured and predicted RMR to be more common in obese individuals than in nonobese individuals, but those individuals who do not conform to standard cannot be identified without actually measuring RMR.”
“The usual clinical maneuver of inserting an adjusted body weight into the Harris Benedict equations corrects the tendency of that equation to overestimate RMR but replaces it with a tendency to underestimate RMR.”

Funding Source:

University/Hospital:

Pennsylvania State University

Reviewer Comments:

Strengths

Wide range of BMI.

Limitations

Self-selection bias—convenience sample with volunteers
Limited generalizability—98% Caucasian; not representative of general population
Traveling to research center before measurement rather than spending night in facility (?); might affect RMR; did not discuss length of time of rest before measurement (was it long enough?)
Did the researchers control for physical activity (56% had sedentary lifestyles and 46% had recreational physical activity; intensity??)
Small sample sizes when divided into groups
Limitations of study not discussed.

Quality Criteria Checklist: Primary Research
Relevance Questions
	1.	Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies)	Yes
	2.	Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?	Yes
	3.	Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice?	Yes
	4.	Is the intervention or procedure feasible? (NA for some epidemiological studies)	Yes

Validity Questions
1.	Was the research question clearly stated?		Yes
	1.1.	Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?	N/A
	1.2.	Was (were) the outcome(s) [dependent variable(s)] clearly indicated?	N/A
	1.3.	Were the target population and setting specified?	N/A
2.	Was the selection of study subjects/patients free from bias?		Yes
	2.1.	Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study?	N/A
	2.2.	Were criteria applied equally to all study groups?	N/A
	2.3.	Were health, demographics, and other characteristics of subjects described?	N/A
	2.4.	Were the subjects/patients a representative sample of the relevant population?	N/A
3.	Were study groups comparable?		N/A
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	N/A
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	N/A
	3.4.	If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis?	N/A
	3.5.	If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.)	N/A
	3.6.	If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")?	N/A
4.	Was method of handling withdrawals described?		No
	4.1.	Were follow-up methods described and the same for all groups?	N/A
	4.2.	Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.)	N/A
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	N/A
	4.4.	Were reasons for withdrawals similar across groups?	N/A
	4.5.	If diagnostic test, was decision to perform reference test not dependent on results of test under study?	N/A
5.	Was blinding used to prevent introduction of bias?		No
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	N/A
	5.2.	Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.)	N/A
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	N/A
	5.4.	In case control study, was case definition explicit and case ascertainment not influenced by exposure status?	N/A
	5.5.	In diagnostic study, were test results blinded to patient history and other test results?	N/A
6.	Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described?		Yes
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	N/A
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	N/A
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	N/A
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	N/A
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	N/A
	6.6.	Were extra or unplanned treatments described?	N/A
	6.7.	Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?	N/A
	6.8.	In diagnostic study, were details of test administration and replication sufficient?	N/A
7.	Were outcomes clearly defined and the measurements valid and reliable?		Yes
	7.1.	Were primary and secondary endpoints described and relevant to the question?	N/A
	7.2.	Were nutrition measures appropriate to question and outcomes of concern?	N/A
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	N/A
	7.4.	Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?	N/A
	7.5.	Was the measurement of effect at an appropriate level of precision?	N/A
	7.6.	Were other factors accounted for (measured) that could affect outcomes?	N/A
	7.7.	Were the measurements conducted consistently across groups?	N/A
8.	Was the statistical analysis appropriate for the study design and type of outcome indicators?		Yes
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	N/A
	8.2.	Were correct statistical tests used and assumptions of test not violated?	N/A
	8.3.	Were statistics reported with levels of significance and/or confidence intervals?	N/A
	8.4.	Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)?	N/A
	8.5.	Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?	N/A
	8.6.	Was clinical significance as well as statistical significance reported?	N/A
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	N/A
9.	Are conclusions supported by results with biases and limitations taken into consideration?		No
	9.1.	Is there a discussion of findings?	N/A
	9.2.	Are biases and study limitations identified and discussed?	N/A
10.	Is bias due to study's funding or sponsorship unlikely?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	N/A
	10.2.	Was the study free from apparent conflict of interest?	N/A