Camila Orsso | ALES Graduate Seminar

Date(s) - 02/07/2020
9:30 am - 10:30 am

A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Camila Orsso. This seminar is open to the general public to attend.

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Meeting ID: 973 6887 7528

Password: ORSSO

Thesis Topic: Body Composition Assessment in Pediatric Obesity: Reliability, Validity, and Clinical Applications

MSc with Drs. Andrea Haqq and Carla Prado.

Seminar Abstract:

Adipose tissue and skeletal muscle have unique metabolic roles. Despite body mass index for age and sex (BMI z-score) being widely used to evaluate and monitor health status in children with obesity, it does not depict adiposity and muscularity (or their changes) during growth or weight loss interventions. Thus, using body composition techniques to identify metabolic risk factors and evaluate the effectiveness of obesity interventions is a more meaningful approach.

The first goal of this research was to summarize the reliability and validity of laboratory and field techniques used for body composition assessment in children with overweight and obesity. A systematic review of 66 studies revealed that laboratory techniques, such as air-displacement plethysmography (ADP) and dual-energy X-ray absorptiometry (DXA), had high reliability to assess variables describing both adiposity (i.e. percent body fat [%BF], fat mass [FM]) and muscularity (i.e. fat-free mass [FFM]). Furthermore, small bias combined with clinically acceptable limits of agreement (≤5%) were found for %BF measured by ADP (bias range= -0.4% to 3.17%), DXA (bias range= 1.0% to 2.2%), and isotope dilution (bias range= -2.7% to 2.7%) compared to multicompartment models in Bland-Altman analyses. Regarding field techniques, ultrasound (US) was found as a reliable technique to assess skeletal muscle and adiposity (in visceral and subcutaneous depots) as well as a valid technique for %BF estimation (bias range= -0.4% to 0.1%, compared to DXA). On the other hand, skinfolds and BIA (also known as field techniques) showed large bias (ranging from -12.7% to -0.1% and -7.1% to 3.6%, respectively) with unacceptable limits of agreement for %BF estimation (>5%), whilst skinfolds presented with good reliability to measure thickness at different body sites. These findings suggest that laboratory techniques should not be replaced by field techniques, except for US, when assessing body composition in children with excess adiposity.

The second goal of this research was to evaluate the extent to which body composition parameters (i) varied across BMI z-score values and metabolic health status, and (ii) associated with metabolic risk factors in children with obesity. Whole-body and segmental body composition were assessed using ADP and US (at the midthigh level), respectively; the load-capacity index (LCI) was calculated as the ratio between adiposity and muscularity. Children with similar BMI z-scores had a large variability in body composition; e.g. males with BMI z-score between 3 to 4 SD had a variation of 42.9% in FM index (adjusted for height squared), 21.4% in FFM index, and 33.7% in LCI by ADP. Children with high LCI had greater concentrations of markers of insulin resistance (IR; i.e. homeostatic model assessment of IR [HOMA-IR]; p=0.041) and low-grade inflammation (i.e. high-sensitivity c-reactive protein [hs-CRP]; p<0.001). Moreover, we found that HOMA-IR was positively associated with FFM index (R2=0.45; p=0.002) to a greater extent than FM index (R2=0.33; p=0.028), independent of sexual maturation. However, the associations were lost after adjusting for the effects of muscle echo intensity (mEI; a surrogate of ectopic fat in muscles; hence, muscle “quality”). In fact, mEI explained 43% of the variation in HOMA-IR (p=0.018) and 49% of the variation in hs-CRP (p=0.004).

The major finding of this research was that compared to children with obesity alone, those with obesity and metabolic dysfunction had lower muscle “quality” rather than lower muscle “quantity”. As BMI z-score and two-compartment body composition models (e.g. ADP, DXA) cannot distinguish ectopic fat in muscles from whole-body adiposity, the US technique may have a greater clinical utility. However, future studies should evaluate the agreement between US and imaging techniques in depicting segmental body composition in pediatric obesity populations. These findings will contribute to advancing the field of pediatric body composition assessment, design of trials investigating obesity intervention effectiveness, and improve care of children living with obesity.