ENERGY REGULATION DURING THE ADULT LIFESPAN
Location: Human Nutrition Research Center on Aging
Title: Effect of body composition methodology on heritability estimation of body fatness
| Elder, Sonya J. - |
| Roberts, Susan B. - |
| Mccrory, Megan A. - |
| Das, Sai Krupa - |
| Fuss, Paul J. - |
| Pittas, Anastassios G. - |
| Greenberg, Andrew S. - |
| Heymsfield, Steven B. - |
| Dawson-Hughes, Bess - |
| Bouchard, Thomas J. - |
| Saltzman, Edward - |
| Neale, Michael C. - |
Submitted to: Open Nutrition Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 15, 2011
Publication Date: February 28, 2012
Citation: Elder, S., Roberts, S., Mccrory, M., Das, S., Fuss, P., Pittas, A., Greenberg, A., Heymsfield, S., Dawson-Hughes, B., Bouchard, T., Saltzman, E., Neale, M. 2012. Effect of body composition methodology on heritability estimation of body fatness. Open Nutrition Journal. 6:48-58.
Interpretive Summary: The etiology of obesity and overweight is clearly multifactorial, but the relative influence of genes versus the environment in affluent societies with high rates of obesity remains uncertain and may be changing. The objectives of this study were to assess the effects of six body composition methodologies and three body fatness expressions on the heritability of body fatness, and to identify the methods and expressions that introduce the least bias. This work was part of a new cross-sectional investigation of the heritability of energy regulation measures in a population of identical twins reared apart (MZAs) or reared together (MZTs).This study of body fatness heritability in a unique population of MZAs and MZTs showed that genetics accounts for a lower (60%) and unique environmental factors account for a higher estimate of variability (about 20%)) than many previous studies. This difference can be attributed to the identification of appropriate body composition methods and expressions (Bone density (DXA) and total body water with fatness expressed as fat mass/height2) to minimize bias. Body fatness measured using these techniques appears to be substantially less heritable than other body parameters such as height and chest circumference, emphasizing the importance of environmental factors and possibly genotype by environmental interactions in the etiology of weight gain and the obesity epidemic.
Heritability estimates of human body fatness vary widely and the contribution of body composition methodology to this variability is unknown. The effect of body composition methodology on estimations of genetic and environmental contributions to body fatness variation was examined in 78 adult male and female monozygotic twin pairs reared apart or together. Body composition was assessed by six methods – body mass index (BMI), dual energy x-ray absorptiometry (DXA), underwater weighing (UWW), total body water (TBW), bioelectric impedance (BIA), and skinfold thickness. Body fatness was expressed as percent body fat, fat mass, and fat mass/height2 to assess the effect of body fatness expression on heritability estimates. Model-fitting multivariate analyses were used to assess the genetic and environmental components of variance. Mean BMI was 24.5 kg/m2 (range of 17.8-43.4 kg/m2). There was a significant effect of body composition methodology (p<0.001) on heritability estimates, with UWW giving the highest estimate (69%) and BIA giving the lowest estimate (47%) for fat mass/height2. Expression of body fatness as percent body fat resulted in significantly higher heritability estimates (on average 10.3% higher) compared to expression as fat mass/height2 (p=0.015). DXA and TBW methods expressing body fatness as fat mass/height2 gave the least biased heritability assessments, based on the small contribution of specific genetic factors to their genetic variance. A model combining DXA and TBW methods resulted in a relatively low FM/ht2 heritability estimate of 60%, and significant contributions of common and unique environmental factors (22% and 18%, respectively). The body fatness heritability estimate of 60% indicates a smaller contribution of genetic variance to total variance than many previous studies using less powerful research designs have indicated. The results also highlight the importance of environmental factors and possibly genotype by environmental interactions in the etiology of weight gain and the obesity epidemic.