EAL

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To develop IC protocol that is practical for use in large-scale studies and produce reliable estimates of RMR in free-living, postmenopausal women. Specifically, addressed the length of the data collection period, the value of duplicate measures, and the pros and cons of conducting IC until achievement of specific steady state criteria.

Definitions

Postmenopausal: was defined as greater than or equal to 55 y of age or at least 12mo since last menses.
Steady state: was defined as 10 min during which the volume of oxygen consumed, variation in minute ventilation (VE) and RQ did not vary >10%. If 10 min of steady state was not achieved by 30 min data collection, the test was continued until 10 min of ‘steady state’ was achieved or at 45 min of data collection, whichever occurred first.

Inclusion Criteria:

Understand and give written consent
Free-living, postmenopausal women

Exclusion Criteria:

Refusal to consent
Not meeting inclusion criteria
Subjects that were excluded: bowel disease, diabetes, hypoglycemia, renal disease, liver disease, claustrophobia, weight change in excess of 4.5 kg in the 2 mo before enrolment and alcohol intake >2 servings per day.

Description of Study Protocol:

Subjects were scheduled for 2 fasting visits 1 wk apart. Each subject completed 24h urine collection before each visit. RMR was measured using a VMAX 2900 IC. One trained technician conducted all IC measurements.

Body composition was estimated using urinary creatinine from duplicate 24-h urine collections.

ANTHROPOMETRIC

Ht, Wt, hip and waist measurements

CLINICAL

IC measurements: Measured REE [(VO₂ l/min), VCO₂ (l/min; ml/kg/min), RQ, ventilation (l/min)].

Resting energy expenditure

IC type: VMAX2900
Equipment of Calibration: Sensormedics
Coefficient of variation using std gases: Yes or no
Rest before measure (state length of time rested if available): 30 min.
Measurement length: (Steady state) 10 min during which the volume of oxygen consumed, VE and RQ did not vary >10%
Fasting length: 8h prior to measurements
Exercise restrictions XX hr prior to test? 48 hr
Room temp: thermally neutral
No. of measures within the measurement period: data points were collected every 30 s
Were some measures eliminated? Not specified
Coefficient of variation in subjects measures? No
Training of measurer? Yes
Subject training of measuring process? Yes

Data Collection Summary:

Outcome(s) and other measures

Compared RMR for 0-5, 5-10, 5-15, 5-20, 5-25, 5-30, and 0- to 30-minutes IC segments and segments meeting stability criteria.
Height, weight, hip and waist circumference
24 hr urine collection

Blinding used: No

Description of Actual Data Sample:

N=102 women 50-79 years of age
Mean age: 62.5±8.2 y; 94% Caucasian

Statistical tests

RMR for segments had near normal distributions with slight left shifts; used the natural logarithmic transformation of all RMR to improve normal distribution approximations, followed by paired t test comparison. Pearson correlation coefficients

Summary of Results:

ANTHROPOMETRIC

31% BMI<23.1
34% BMI between 23.1 and 27.3
20% overweight, BMI between 27.3-32.2
15% obese, BMI>32.2
FFM: 47.3±4.7kg
% body fat: 32.4±10%

RMR from 5-10 minutes was positively correlated with FFM (r=0.62, P<0.0001), BMI (r=0.83, P<0.0001) and % body fat (r=0.36, P<0.0002). Relationships between these measures and the mean RMR recorded from 5 to 30 minutes were almost identical.

The mean RMR for the first 5 min was significantly higher than other time segments (P=0.001). Correlation coefficients between duplicate measures were high (r=0.90).

Cumulative % subjects achieving criteria (minus first 5 min)

	15 minutes	30 minutes	45 minutes
Visit 1 <5% variation for 5 min	23	34	39
10 min	2	2	2
<10% variation for 5 min	82	93	94
10 min	32	47	58

Stringent steady-state criteria (10 min with VO₂ VE, and RQ varying <5%) were too difficult for most women to achieve even after 45 min of data collection. Conversely, nearly all women (94%) achieved 5 min with <10% variability in VO₂ VE, and RQ.

In general, more subjects achieved steady state criteria more quickly and more often at visit 2 than at visit 1. 84% of women achieved 5 min with <10% variability in VO₂ VE, and RQ in 15 min; 65% achieved <10% variation for 10 minutes variability in VO₂ VE, and RQ in 45 min; Slightly less than half (43%) achieved <5% variation for 5 minutes within the first 45 min; and only 4% achieved this variation for 10 minutes in the first 45 min.

For subjects not achieving 10 min with <10% variability in VO₂ VE and RQ by 30 min, we observed a mean increase of 3-6 kcal in RMR when we continued IC until either this criteria was achieved or 45 min elapse (P=0.005).

Compared with visit 1, RMRs were lower at visit 2 for the 0-5 min (p=0.001), 5-15 (P=0.04) and 0 to 30 min (P=0.05) segments. RMRs calculated from the full length of IC were lower for visit 2 (P=0.06).

Use of defined stability criteria produced.

COMPARISON TO PREDICITON FORMULAS

Predicted RMRs were 100-200 kcal higher than measured values using the 5- to 10 min segment of IC from each visit and a two-visit mean (P=0.001) RMR measured from segments that met the three achievable definitions of steady-state were 10-30 kcal closer to predicted values; however, differences between measured and predicted RMR remained (P<0.02).

	Visit 1 (kcals)	Range (kcals)
HB	177±108	-167-477
Mifflin	102±114	-218-382
WHO	236±112	-89-491
	Visit 2 (kcals)	Range (kcals)
HB	187±102	-92-434
Mifflin	112±106	-145-419
WHO	246±102	-46-493
	2-visit (kcals)	Range (kcals)
HB	179±99	-143-435
Mifflin	104±102	-180-340
WHO	238±101	-98-449

RMR measures from segments that met the three achievable definitions of steady state were 10-30 kcal closer to predicted values; Differences between measured and predicted RMR remained (P<0.02).

Author Conclusion:

“Data suggested that IC measurements longer than 10 min offer little improvement in RMR estimates.”

“conducting IC to achieve predetermined steady-state criteria offered few improvements in RMR accuracy, increased subject burden and would reduce sample size because some subjects were unable to meet the criteria.”

“Small differences in mean RMR seen when IC is conducted for various lengths of time, although statistically significant, are likely to be inconsequential in the overall TE calculation that includes the highly variable activity-related energy expenditure component.”

“More reactive RMR data during the first 5 min of measurement, suggesting it may not reflect RMR and should be discarded.”

“At the second visit, more subjects were able to achieve stability criteria by 20 min and there was a 10-20 kcal reduction in mean RMR compared with the first visit; nonetheless, the average difference in RMR between the two visit measures was <20 kcal and correlation coefficients between the two visits were ~0.90, which suggest that doing a second measure is of limited value.”

“Limitations include comparing time segments of continuous IC studies instead of conducting studies of various lengths on each subject, which may underestimate differences that occur when the shorter measures are taken; only assess RMR using IC study lengths, duplicate measures and 3 steady-state criteria definitions; Did not explore various lengths of relaxation before measurements.”

“For public health protocol including IC to assess RMR as a component of TEE in post menopausal women, a 10-min canopy study (excluding the first 5 min of data collection) produced reliable results with minimal subject burden.”

“Use of steady state criteria (i.e., achieved 5 min of <10% criteria variation by 45 min offered no additional precision and clinically unimportant differences in mean RMR measures.”

Funding Source:

Government:

National Cancer Institute

Reviewer Comments:

Strongly agree with author’s conclusion.

Strengths

Well-defined population and well set inclusion/exclusion criteria.
Controlled for diet and physical activity before each measurement.
One trained technician performed the IC measurement, increased the reliability/consistency of the measurements.
Limitations were fully discussed.

Generalizability/Weaknesses

Generalizability may be limited to free-living, postmenopausal women.

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?		Yes
	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?		Yes
	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?		Yes
	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