FNOA: Assessment of Overweight/Obesity (2012)

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

To determine whether body mass index and waist circumference are good surrogate measures for either total body fat or visceral fat area in older persons.

Inclusion Criteria:
  • Participant in the Health, Aging and Body Composition Study (HEALTH ABC)
  • Aged 70 to 79 years
  • Had complete preliminary data on the variables used in this analysis
  • Free of disability (reported twice that they had no difficulty walking 1/4 mile, walking up 10 steps without resting and also no difficulty with mobility-related Activities of Daily Living).
Exclusion Criteria:
  • Did not participate in the HEALTH ABC study
  • Age less than 70 years or greater than 79 years
  • Had incomplete data on the variables used in this analysis
  • Presence of a disability at baseline.
Description of Study Protocol:
  • Recruitment: Recruitment for the HEALTH ABC cohort began in 1996 at two field centers, the University of Pittsburgh and the University of Tennessee, Memphis
  • Design: Cross-sectional analysis of cohort data
  • Blinding used (if applicable): Implied with measurements.

Statistical Analysis

  • Pearson correlation coefficients for the anthropometric measures vs. total body fat and vs. visceral fat were calculated
  • Regression equations were calculated by gender for each of the anthropometric variables, using total body fat and then visceral fat as the dependent variables, adjusting for age, field center site and race. The association of a linear term was first tested and then a quadratic term was explored to look at possible improved fit of the model.
Data Collection Summary:

Timing of Measurements

A baseline examination was conducted, in which a medical history was taken, height and weight were measured and BMI was calculated. Several measures of body fat and anthropometric measurements were taken.

Dependent Variables

  • Total body fat
  • Visceral fat
  • Total and regional body fat were measured by dual-energy X-ray absorptiometry. Visceral and subcutaneous abdominal fat and well as thigh subcutaneous fat and thigh intermuscular fat were quantified from the scans.

Independent Variables

  • Height, weight and BMI
  • Waist circumference
  • Thigh circumference
  • Sagittal diameter.

Control Variables

  • Age
  • Field center site
  • Race.
Description of Actual Data Sample:
  • Initial N: 2,830 (1,439 women and 1,391 men)
  • Attrition (final N): All included in cross-sectional analysis
  • Age: 70 to 79 years
  • Ethnicity: 1,642 white participants and 1,188 black participants
  • Other relevant demographics: None.

Anthropometrics

  • Mean weight: 70.4kg for women and 81.4kg for men
  • Mean BMI: 27.6kg/m2 for women and 27.1kg/m2 for men
  • Mean total fat: 27.0kg for women and 21.2kg for men
  • Mean visceral fat: 130.6cm2 for women and 154.31cm2 for men.

Location

Two field centers in Pittsburgh, PA and Memphis, TN, USA.

 

Summary of Results:

Key Findings

  • Among men, sagittal diameter had the strongest correlation with visceral fat
  • Sagittal diameter and waist circumference had approximately equal correlation in women with visceral fat
  • When waist circumference was regressed on body mass index to remove the effect of weight, waist circumference was still poorly-related to visceral fat
  • In women, the largest R2 was for regression of body weight or body mass index on total body fat
  • In men, all of the anthropometric measures were about equal in terms of R2 for total body fat
  • Among women, all of the anthropometric measures (weight, BMI and waist circumference) explained about 40% of the variance in visceral fat
  • For men, sagittal diameter had the largest R2: 62% for any of the anthropometric variables on visceral fat.

Correlation Between Anthropometric Measures and Body Fat

  Women Men

Total Fat

Visceral Fat

Total Fat

Visceral Fat

BMI
0.91**
0.56**

0.86**

0.59**
Waist
0.80**
0.61**
0.83**
0.66*
Waist/Thigh
-0.05
0.33**
0.28**
0.41**
Sagittal diameter
0.74**
0.59**
0.85**
0.72**

**P<0.0001.

Regression of Linear and Quadratic Terms: Total Fat

  Women Men

Linear (β)

Quadratic (β)

Linear (β)

Quadratic (β)

Weight2
--
-0.001**
--
-0.002**
Weight (kg)
0.59**
0.73**
0.44**
0.82**
R2
0.88
0.88
0.74
0.76
BMI2
--
-0.003**
--
-0.014**
BMI (kg/m2)
1.55**
1.99**
1.49**
2.31**
R2
0.84
0.84
0.75
0.75
Waist2
--
-0.001**
--
-0.003**
Waist
0.55**
0.00
0.50**
1.21**
R2
0.69
0.69
0.69
0.75
Sagittal2
--
-0.028**
--
0.038**

Sagittal

1.69**
3.45**
1.92**
0.18
R2
0.55
0.68
0.73
0.74

P<0.001, adjusted for age, race and sex.

Regression of Linear and Quadratic Terms: Visceral Fat

  Women Men

Linear (β)

Quadratic (β)

Linear (β)

Quadratic (β)

Weight2
--
-0.03**
--
-0.02**
Weight (kg)
2.71**
6.71**
3.03**
6.23**
R2
0.38
0.40
0.41
0.42
BMI2
--
-0.21**
--
-0.19**
BMI (kg/m2)
7.25**
19.61**
10.78**
21.90**
R2
0.38
0.40
0.45
0.46
Waist2
--
-0.00**
--
-0.03**
Waist
2.92**
3.68
3.95**
10.24**
R2
0.40
0.40
0.49
0.53
Sagittal2
--
-0.20**
--
0.06**
Sagittal
10.40**
23.17**
17.00**
14.08
R2
0.41
0.55
0.62
0.62

P<0.001, adjusted for age, race and sex.

Author Conclusion:
  • In this population of healthier older persons aged 70 to 79 years, body weight and body mass index appear to be good indicators of total body fat, based on correlations, graphical data and regression modeling
  • Waist circumference and sagittal diameter were more strongly-correlated with total body fat than visceral fat. Adjusting waist circumference for BMI did not appear to correct this problem.
  • Adding quadratic terms to linear models for the anthropometric variables increased the R2 only for sagittal diameter in women and for waist circumference in men. The variables still remained more closely-related to total body fat.
  • The use of waist circumference or sagittal diameter as surrogate measures for the visceral fat area is problematic.
Funding Source:
Government: Epidemiology, Demography and Biometry Program of the National Institutes on Aging
Reviewer Comments:

Results apply to healthy, free-living older individuals.

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) N/A
  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) N/A
 
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? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
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? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
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) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  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? Yes
  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.) Yes
  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? Yes
  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%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  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? Yes
  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.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  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? Yes
  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? Yes
  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? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
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? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  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)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  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? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes