EAL

FNOA: Assessment of Overweight/Obesity (2012)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To assess associations of performance-based and self-reported physical function with absolute levels of lean and fat mass independently of each other and of overall body size.

Inclusion Criteria:

Reside in or near Sonoma, California
Participated in a baseline assessment for a cohort study investigating the effect of aging on physiologic capacity and physical function in 1992
Community dwelling
Age 55 years or older at time of baseline assessment.

Exclusion Criteria:

Aged younger than 55 years
Resident of an institution.

Description of Study Protocol:

Recruitment

All eligible participants were contacted following identification by a community-based census. 68.4% of eligible participants agreed to joining the cohort. This paper in a cross-sectional analysis of a baseline examination completed at time of cohort entry.

Design

Cross-sectional analysis of cohort.

Statistical Analysis

Pearson correlation coefficients provided a crude measure of the collinearity among pairs of body composition, body size and fat distribution. Residual variables were defined from linear regression analysis to allow for an evaluation of the distinct contribution to physical function that each part of body composition provides.
Analysis of variance was conducted with least-square means and 95% confidence intervals to examine mean differences in body composition and fat distribution by level of physical performance, adjusting for age and co-morbidity
Multivariable linear or logistic regression models were performed to evaluate the estimates of the independent associations between physical performance and fat mass, height, residual lean mass and residual waist circumference
All analyses were stratified by gender.

Data Collection Summary:

Timing of Measurements

All measurements were taken during a baseline examination.

Dependent Variables

Walking speed (number of feet walked in 60 seconds)
Grip strength (in dominant hand in kilograms with a hydraulic hand grip dynamometer)
Self-reported functional limitation (series of 10 questions measuring difficulty).

Independent Variables

Fat mass (bioelectrical impedance)
Lean mass (bioelectrical impedance
Height (measured)
Weight (measured)
Waist circumference (measured at natural waist).

Control Variables

Age
Co-morbidity
Self-reported physical activity
Smoking status.

Description of Actual Data Sample:

Initial N: Original sample consisted of 2,092 men and women
Attrition (final N): 947 women and 708 men included in the analysis
Age: Greater than 55 years old (mean age 69.3 years for women and 69.5 years for men)
Ethnicity: Predominately white (96.6%)
Other relevant demographics: Well-educated (40.4% with at least a college degree), relatively affluent (21.8% with incomes higher than $50,000 per year)
Anthropometrics: Women were shorter, lighter and with less lean mass and more fat mass than men. Women had a smaller mean waist circumference and had a lower level of reported physical activity than men.
Location: Sonoma, CA, US.

Summary of Results:

Key Findings

Associations of body composition and fat distribution with physical performance and self-reported functional limitation (mean differences by ANOVA with least square means):

Fat mass (26.3 vs 28.7kg and 21.8 vs. 24.0kg in women and men, respectively; P<0.0001) and waist circumference (82.6 vs 86.3cm and 96.6 vs. 100.3 cm in women and men, respectively; P<0.0001) were significantly lower in those with a faster walking speed
Fat mass (25.7 vs. 31.3kg and 22.2 vs. 25.2kg in women and men, respectively; P<0.0001) and waist circumference (82.2 vs. 89.3cm and 97.3 vs. 103.2cm in women and men, respectively; P<0.0001) were significantly lower in those with no self-reported functional limitation
Lean-to-fat ratio was significantly higher in those with a faster walking speed (1.57 vs. 1.46kg; P<0.001; and 2.90 vs. 2.66kg; P<0.0005 in women and men, respectively) and in those with no self-reported functional limitation (1.60 vs. 1.35kg and 2.85 vs. 2.49kg in women and men, respectively; P<0.0001)
Greater grip strength was significantly associated with greater lean mass (39.4 vs. 37.3kg and 59.4 vs. 56.8kg in women and men, respectively; P<0.0001)
Greater drip strength was not associated with lean-to-fat ratio, fat mass or waist circumference.

Independent associations of body composition and fat distribution with physical performance and self-reported functional limitation (multi-variable linear or logistic regression):

Walking speed remained inversely associated with fat mass (β=-0.009, SE=0.001 and -0.009, SE=0.002 in women and men, respectively) and waist circumference (β=-0.006, SE=0.002 and -0.001, SE=0.003 in women and men, respectively)
Walking speed was no longer inversely associated with lean mass, but showed a direct association in men (β=0.011, SE=0.004)
No relationship was seen between reported functional limitation and lean mass
Reported functional limitation was positively related to fat mass (OR=1.08, 95% CI: 1.06, 1.10 and OR=1.09, 95% CI: 1.05, 1.12; P<0.01 for women and men, respectively) and waist circumference (OR=1.03, 95% CI: 1.00, 1.07 and OR=1.06, 95% CI: 1.00, 1.12; P<0.05 for women and men, respectively)
In women, relations between grip strength and absolute measures of body composition varied by fat mass. Lean mass was directly associated with grip strength in all women, the magnitude of the association became less as fat mass increased (P for interaction between lean mass and fat mass =0.0001, β=-0.025). Grip strength in women was not associated with the lean-to-fat ratio. Grip strength was positively associated with waist circumference (β=-0.142, SE=0.046; P<0.01).
In men, relations between grip strength and body composition varied by age. The magnitude of grip strength associated with an increased lean mass was greater in older men (β=0.367 in younger men and 0.865 in older men). Fat mass was not associated in either age group. Waist circumference and lean-to-fat ratio was inversely associated with grip strength only in older men.

Other Findings

Interrelations of body composition, body size and fat distribution (rationale for use of residual variables):

Weight was almost entirely collinear with fat mass (R=0.97 and 0.95 in women and men, respectively)
Weight was directly related to lean mass (R=0.88 and 0.94 in women and men, respectively) and waist circumference (R=0.83 and 0.85 in women and men, respectively)
Weight was inversely related to the lean-to-fat ratio (R=-0.76 and -0.71 in women and men, respectively)
Height showed a modest correlation with fat mass (R=0.27 and 0.28 in women and men,respectively) and a substantial correlation withe lean mass (R=0.59 and 0.54 in women and men, respectively)
Lean mass and fat mass were highly, positively correlated with each other (R=0.75 and 0.78 in women and men, respectively)
Lean mass was correlated with waist circumference (R=0.64 and 0.71 in women and men, respectively)
Fat mass was correlated with waist circumference (R=0.86 and 0.89 in women and men, respectively).

Author Conclusion:

Fat mass negatively impacts some domains of physical performance and overall functioning, while lean mass is less significant in absolute terms but is important relative to amount of body fat
Higher fat mass was associated with slower walking speed and greater likelihood of functional limitation
The part of lean mass not accounted for by height or fat mass was not associated with these outcomes, except for a small direct association with walking speed in men
Accumulation of body fat may be more predictive of poor physical performance, functional limitation and subsequent disability than loss of muscle mass. The analytical approach in the study, which attempted to separate out that part of each body composition and fat distribution variable not accounted for by the other variables and by overall body size perhaps allowed for greater precision of estimates of independent associations.

Funding Source:

Government:

National Institute on Aging

Reviewer Comments:

Cohort studied was predominately middle to upper-middle class, White and well educated. Generalization to the elderly population as a whole is limited.
Sample was self-selected (44% of non-participants returned a questionnaire indicating that they were similar to participants in terms of age and medical conditions, but were less educated and more likely to be former or current smokers)
Cross-sectional design limits ability to make cause-and-effect judgments.

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.)	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?		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.)	No
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	No
	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?		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?	N/A
	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