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Healthy Non-Obese Adults (2010-2012)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

  1. Measure basal energy expenditure in a group of healthy individuals using direct and indirect calorimetry methods
  2. Compare to predicted basal energy expenditure using Harris Benedict equation.
Inclusion Criteria:
  1. Healthy
  2. Adults (men and women)
Exclusion Criteria:
  1. Subjects who were less than 90% or greater than 125% of ideal body weight (IBW)
  2. History of recent weight loss
  3. Subjects with unusual dietary practices (not defined)
  4. Subjects with endocrine disorders
  5. Subjects with pharmacologic therapy
  6. women on hormonal treatment
Description of Study Protocol:

Anthropometrics:

height and weight (not discussed as to whether measured or self-reported)

Clinical:

None discussed

Basal Energy Expenditure:

Measured in 2 subject pools using three calorimeters; by 2 methods—Indirect Calorimetry (IC) and Direct Calorimetry (DC)

Measurements of IC and DC done after subjects arrived at research centers; did not sleep at centers

Direct Calorimetry

How: Direct gradient-layer whole body instrument with a chamber size of 2.4 m3

Measurement length: 60-90 minutes with subject resting quietly inside the chamber

The basal energy expenditure was taken as the heat release following 10 to 15 minutes of stable readings

Radiant heat losses were measured with the gradient-layer within the walls of calorimeter

Calibrated by standard heat source

Prior studies using variety of wet and dry heat sources indicate the calorimeter is accurate to within 1 to 2%.

Indirect Calorimetry: (2 different IC calorimeters)

Type:  At Emory University—expired air measured  with a variable orifice pneumotachograph, and respiratory gases were collected by means of a tightly applied facemask, nonrebreathing valve, and meterological balloon.

At Memorial Sloan-Kettering Medical Center—metabolic measurement cart:

Rest before measurement: At Emory University, IC done at end of direct calorimetry, where subject rested quietly during measurement period.  At Memorial Sloan-Kettering, IC followed 15-30 minute resting period

Measurement length: At Emory; not discussed;  At Memorial Sloan-Kettering; measurements were monitored every 2 minutes until stable for at least 6 minutes; the three final results were averaged, providing a mean for each measurement

Fasting length before measurement: For both centers—12 hours overnight

Exercise conditioning prior to test? Not discussed

Room temperature: Not discussed

Coefficient of variation? At Emory, the accuracy of the pneumotachograph was compared to a Tissot spirometer at 3 volumes and results indicated a difference of less than 1.5%

Calibration of instrument: At Emory—routine calibration prior to each study using a .5 L syringe and primary standard calibration gases; Memorial Sloan-Kettering—instrument calibrated using a 1-L volumetric syringe and primary standard calibration gases.

Training of measurer: Not mentioned

Subject given prior training of IC to minimize anxiety? Not mentioned.

Dietary measures: None used.

Statistics:

  • Correlations between predicted and measured basal energy expenditure for all calorimetry methods.
  • Regression analysis.
  • Significance set at p <0.05.
Data Collection Summary:

Was blinding used? No

  1. Measured basal energy expenditure using IC and DC
  2. With DC, basal energy expenditure was taken as the heat release following 10 to 15 min of stable readings
  3. At Memorial Sloan Kettering, a computer program was used to calculate VO2, VCO2, and R. These measurements were monitored every 2 min until stable for at least 6 min; the three final results were averaged; providing a mean value for each measurement.
  4. At Emory, VO2, VCO2, and R were calculated from measured minute volume and fractions of expired oxygen and carbon dioxide.
  5. At both centers, energy expenditure in kcal min –1 was derived by multiplying VO2 by a factor representing the caloric value of 1 L of oxygen for the pertinent R value. The resulting basal energy expenditure in kcal min-1 was then extrapolated to 24 h. This measured rate of basal energy expenditure was then compared to the corresponding value predicted by the Harris-Benedict equation.
Description of Actual Data Sample:

Total of 127 healthy subjects (68 F, 59 M) between the ages of 18 and 67

Subjects were evaluated at 2 medical centers: Emory University School of Medicine and Memorial Sloan-Kettering Cancer Center

The group from Emory was enrolled at the Calorimetry Facility and the group from Memorial Sloan-Kettering was enrolled at the Metabolic Research Facility.

Emory:  (N = 74; 39 F, 35 M)

Age: 38.8 ± 13.4

Ht (cm):  168.7 ± 15.8

Wt (kg):  71.1 ± 9.4

Body surface (M2) = 1.82 ± 0.13

Basal Energy Expenditure—

Indirect (kcal/d) = 1423 ± 190 (predicted vs. measured, p <0.001)

Direct (kcal/d) = 1378 ± 154 (predicted vs. measured, p <0.001)

Predicted (kcal/d) = 1572 ± 228

Sloan-Kettering: (N = 53; 29 F, 24 M)

Age:  31 ± 7.8

Ht:   171.4 ± 5.8

Wt:  67.4 ± 7.3

Body Surface = 1.78 ± 0.14

Basal Energy Expenditure:

Indirect (kcal/d) = 1399 ± 146 (predicted vs. measured, p <0.001)

Direct (not measured)

Predicted (kcal/d) = 1572 ± 77

Withdrawals not mentioned.

Summary of Results:

Indirect Calorimetry:

At Emory, there was a significant correlation between predicted and measured basal energy expenditure (r = 0.83; p <0.001), but there were significant differences between the two results: the Harris-Benedict overpredicted the measured value by 10.4 + 11.7% (p <0.001, t-test)

The findings were similar at Sloan-Kettering using IC. Predicted and measured basal energy expenditure were significantly correlated (r = 0.82, p <0.001), but a 12.3 + 10.6% (p <0.001) overprediction occurred using the Harris-Benedict equation.

The magnitude of the overprediction remained unchanged when men, women, and different age groups were analyzed separately.

Direct Calorimetry:

At Emory, the use of DC confirmed the findings of IC. There was a significant correlation (r = 0.84, p <0.001) but overprediction of basal energy expenditure by the Harris-Benedict equation (14.1 + 12.6%, p <0.001).

Indirect Calorimetry and Direct Calorimetry:

The correlation at Emory for IC and DC was significant (r = 0.81, p <0.001), and the mean difference between the 2 methods was 3%.

Author Conclusion:

Using DC and 2 different IC, our two centers found that the Harris-Benedict equation overestimated basal energy requirements by 10 to 15% (avg 12.3%).

For some individual patients the overprediction was much larger, in some cases up to 25 or 30%.

The original Harris-Benedict study was meticulous in design, execution, and description, and therefore the differences between our results must be ascribed to technical factors or variations in our subject pools. Our method of analyzing ventilatory volumes and respiratory gases are more sophisticated than those used in the Harris-Benedict study; therefore some of the difference may be accounted for by modernization of equipment. Early workers also noted a training factor, with repeated measurements of energy expenditure on the same subject decreasing by 8-10% from the initial measurement. Subject differences, climatic factors, the level of physical activity, body composition, and foods ingested have all changed over the six decades since completion of the Harris-Benedict study. Whatever the explanation, the problem of accurate prediction of basal energy expenditure in the individual patient remains.

A simple and logical conclusion from our study would be to reduce the predicted basal energy expenditure for an individual patient by about 10%. However, our data, like that of Harris-Benedict, may not be universally applicable.

The results from 15 other studies in which basal energy expenditure measured in healthy non-obese individuals could be compared to a value predicted by the Harris-Benedict equation. There was a wide variability in measured basal energy expenditure than predicted; from –14% to +19%. The specific causes of the variability are unknown, but no doubt both technical and biologic differences combine to produce the observed differences.

In summary, We observed a relatively large difference between one of these estimated values, basal energy expenditure, and the actual value derived by calorimetry. With the current interest in human energy requirements, it would be worthwhile developing predictors of 24 h basal energy expenditure of improved accuracy.

Funding Source:
Government: State of Georgia
Industry:
HJ Heinz Co.
Food Company:
Reviewer Comments:

Strengths:

  • Wide variability in subjects ages

Limitations:

  • Small sample size when split into groups
  • Physical activity not accounted for; might affect results
  • Cross-sectional design does not allow for cause and effect statements
  • Subjects from New York and convenience sample; limited generalizability
  • Used only non-obese individuals
  • Unusual dietary practices( ?)
  • Methodology not clear—ex.  Height and weight-self-reported or measured?
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? No
  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