EAL

FNOA: Assessment of Overweight/Obesity (2012)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

The purpose of this study was to assess the prevalence of normal weight obesity (NWO), according to different cut points in Lausanne, Switzerland.

Inclusion Criteria:

Caucasian men and women aged 35 years to 75 years
Must be of Caucasian origin, meaning that both parents and grandparents were Caucasian
Provide written informed consent
Willing to take part in the examination and to have blood samples drawn.

Exclusion Criteria:

Not of Caucasian ethnicity.

Description of Study Protocol:

Recruitment

A simple nonstratified random selection of the subjects was performed and a random sample of 35% of the overall population was drawn. An invitation letter with a study description and a formulary in a pre-stamped envelope was sent to all subjects. Interested subjects returned the formulary and were contacted telephonically within 14 days by one of the staff members who provided more information about the study and arranged for an appointment.

Design: Cross-sectional study.

Blinding used (if applicable): implied with measurements

Intervention (if applicable): Not applicable

Statistical Analysis

Analysis were performed using Stata 9.2.
Comparisons were performed using Student's t test and analysis of variance for quantitative variables.
X² tests were used for qualitative variables.
Statistical significance was assessed for P<0.05.

Data Collection Summary:

Timing of Measurements

Informed consent was obtained from participants before their arrival at the study clinic
One questionnaire was mailed with the appointments letter and completed by the participant prior to the morning visit
A second questionnaire was applied by interview prior to clinical measurements and blood collection
Data were collected by trained field interviewers in a single visit lasting about 60 minutes at an outpatient clinic at the Centre Hospitalier Universitaire Vaudois in the morning after an overnight fast
Data was collected on smoking, alcohol consumption and physical activity.

Dependent Variables

Prevalence of NWO (Normal Weight Obesity), defined as an excessive body fat associated with a normal body mass index (BMI less than 25kg/m²).

Independent Variables

Body weight and height were measured with participants standing without shoes in light indoor clothes
Body weight was measured in kilograms to the nearest 100g, using a Seca electronic scale
Height was measured to the nearest five mm, using a Seca height gauge
BMI was defined as weight/height²
Waist and hip circumference was also measured
Body composition was assessed by electrical bioelectrical impedance analysis.

Control Variables

Not applicable.

Description of Actual Data Sample:

Initial N: 19,830 subjects
Attrition (final N): 6,188, which represents 43% of eligible responders, 41% of all responders, and 31% of the initially sampled population
Age: Men and women 35 to 75 years
Ethnicity: Caucasian origin, with both parents and grandparents being Caucasian
Other relevant demographics: Percentage born in Switzerland, education, smoking status, physical activity, alcohol drinking, height, weight, BMI, body fat percentage, fat mass index, waist and hip circumference
Anthropometrics: Women also had a lower BMI and waist and hip circumference, but a higher body fat percentage and a higher fat and a higher fat mass index than men. In both genders, body fat levels (expressed in percentage of body weight) increased with age.
Location: Lausanne, Switzerland.

Summary of Results:

Key Findings

Percentage body fat increased with age:

	Age: 34-44 Years	Age: 45-54 Years	Age:55-64 Years	Age: 65-75 Years
Percent body fat in men	20.2±5.4	23.0±5.4	26.3±5.2	28.2±4.6
Percent body fat in women	29.9±7.8	33.1±7.4	36.7±7.5	39.6±6.9

Other Findings

In men, the prevalence of NWO was below 1% for all thresholds used, but in women the prevalence of NWO varied from 1.4 to 27.8%, according to the cut-off used
The prevalence of NWO increased with age when age-independent cut-points were used in women, but not in men.

Author Conclusion:

The prevalence of Normal Weight Obesity (NWO) is low in the Caucasian population of Lausanne and higher in women than in men
The prevalence of NWO in women is also dependent on the cut-point used to define excess body fat and efforts are needed to establish appropriate body fat cut points if the prevalences are to be compared between surveys.

Funding Source:

Industry:

GlaxoSmithKline

Pharmaceutical/Dietary Supplement Company:

University/Hospital:

Faculty of Biology and Medicine of Lausanne, Switzerland

Other:

Reviewer Comments:

Authors note the following limitations:

Only Caucasians were included and it might be necessary to use ethnic-specific cut-points as proposed by others
Assessment of body fat was performed using bioelectrical impedance analysis, which might underestimate the values relative to DXA
Study did not include subjects aged over 75 years and it would have been interesting to assess the prevalence of NWO in this age group
Participation rate was rather low (41%), which might limit generalizability of findings
It has been shown that the NHANES and Geneva bioelectrical impedance analysis equations estimate body composition equally well in men, but showed some discrepancies in women, thus it is likely that the differences in the prevalence of NWO women as derived from the Swiss or USA cut-points might partly be due to differences in estimation methods.

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?		No
	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?	No
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.)	Yes
	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?	Yes
	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?	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?		???
	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?	Yes
	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?	???
	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?	N/A
	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?	No
	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?	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