Section

7

Measuring Body Composition in Population Health Research: Case Studies

Case Study 4 Assessing Adiposity Changes in a Community-Based Healthy Weight Program

Background

A community-based healthy weight program (HWP) conducted in a neighborhood recreation center in an urban area plans to evaluate the effectiveness of its 12-week evidence-based program for children and adolescents aged 6–13 years. The HWP includes goals that are common to many similar programs: providing a safe and trusted setting for children and families who often combat obesity-related stigma, teaching behavior skills to make healthy choices easier, and improving health and social outcomes, as well as weight status. Key components of the evaluation will assess changes in behaviors and adiposity.

Considerations

This community-based HWP operates out of a recreation center with one health coach and one health assistant trained to deliver an existing healthy weight intervention curriculum and collect evaluation data. The program receives referrals from primary care providers and schools in the surrounding areas and self-referrals. Because this program is also reimbursed by health insurers for the services it provides, it must take into consideration the outcomes the insurers want evaluated. In this case, the insurers are primarily focused on results of changes in adiposity of participants.

In order to assess changes in adiposity, the program team will have to collect measurements at a minimum of two timepoints: at baseline and at the of the end of the 12-week program. Methods to assess adiposity changes must therefore be sufficiently sensitive to detecting changes in body composition over time. Given the small sample of 16 participants and the short duration of the intervention (12-weeks), the project team is aware the intervention may not detect changes in body composition. They opt to collect additional measures of health, such as changes in self-esteem, psychological health, and physical fitness, to highlight the overall effects of the intervention.

This two-person team with their limited resources will need to select a method that does not pose a collection burden on staff and allows for measurements to be collected feasibly during the limited hours of the intervention. Because measurements must be collected during the time available for participating in the intervention activities at the center, they must also be taken quickly in order to reduce time taken away from intervention participation. Furthermore, the recreation center has many open public spaces and limited privacy for the project team to conduct measurements, so it is important that measurements are collected in a secure area to avoid embarrassing or stigmatizing the children and adolescents. The project team must also take into consideration that methods need to be acceptable to parents who will provide consent and children who will need to assent.

Method Selection

The study team is aware that height and weight are most frequently used across similar programs to assess changes in adiposity. They are the least intrusive of adiposity assessment methods; require little specialized training and equipment; can be conducted quickly, minimizing the time the child is absent from the intervention; and are relatively low in cost. In addition, because this method is commonly used across pediatric practices to track growth, parents and children are familiar with them. When height and weight are collected, BMI can be calculated. However, the study team recognizes that BMI and related indices do not provide information on body composition, specifically fat and fat-free mass. Additionally, the current version of the CDC growth charts are not intended to be used for BMI z-scores and percentiles above the 97^th percentile because changes in extreme values are compressed into a narrow range of associated z-scores or percentiles that do not reflect meaningful changes.⁶²

Given the limitation of using height and weight in this cohort, the project team considers other options. Skinfold thicknesses are discussed as another possibility; measurements can be limited to two of the most accessible areas of the body such as triceps and subscapular and used to monitor changes in subcutaneous fat, a proxy for body fat. Waist circumference may be included as an index of change in central fat distribution. However, this tends to be more difficult to measure consistently in children who are severely obese. Both skinfold and waist circumference methods require skill and training to conduct, require time to collect measurements, and can be intrusive and embarrassing to the child. Methods that can estimate whole-body fat mass, such as DXA and ADP, would not be feasible in the community-based HWP setting for many reasons, including lack of accessibility, cost, the need for trained/technical staff, and time.

Given the limitation of using BMI with children who are severely obese, the difficulty in finding waist circumference landmarks in children with severe obesity, and the lack of privacy in the HWP, the project team decides to measure triceps and subscapular skinfolds as well as height and weight to calculate BMI. Triceps and subscapular can potentially support changes in BMI as being accounted for by changes in fat or show changes in fat that may not have translated to changes in BMI in this short time frame or with this population of children with severe obesity. Height and weight are typically feasible to assess in a community setting where staff, time, and resources are limited. BMI is also commonly used in other studies and in clinical settings for comparison purposes.

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