UAB Studies Obesity Treatment Response Variability in Humans
The rising prevalence of human obesity worldwide has focused research on a variety of interventions that result in highly varied degrees of weight loss (WL). The advent of genomic testing has quantified estimates of both the contribution of genetic factors to the development of obesity, as well as racial/ethnic variation of risk alleles across subpopulations. More recent studies have examined genetic associations with effectiveness of WL interventions, but to date are unable to explain a large proportion of the variance observed.
Therefore, Dr. Kathryn Kaiser, instructor in the office of energetics at the University of Alabama at Birmingham – collaborating with Dr. Gary Gadbury, adjunct professor in the department of biostatistics, section on statistical genetics – described and provided two illustrations of statistical methods to estimate upper and lower bounds of WL treatment response heterogeneity (TRH) in the absence of genotypic data, using published summary statistics from 66 recent weight-loss studies and a raw data set from one large study of 18 months duration.
Thirty-two studies of the 66 studies resulted in some evidence of a positive mean treatment effect with respect to the control group, while the other 34 did not. Data from 12 of these 32 studies with a positive mean effect indicated WL TRH; of these 12, a total of three demonstrated an estimated proportion of greater than 5 percent of the sampled population having an outcome opposite the expected effect (weight gain rather than weight loss). In the raw data set, bounds estimations for change in waist circumference revealed tighter ranges in men than in women. A larger proportion of the sample of women were observed to have an increase in waist circumference over the 18 months of the study despite being in the treatment group, while fewer men demonstrated the same effect. Gender and genetic differences, along with multiple other factors, may interact to reduce average outcomes in WL studies.
Dr. Kaiser concluded that future studies may be able to take advantage of multiple approaches, including the method she employed, to identify and quantify the presence of TRH in studies of WL or related outcomes. “Estimating the Range of Obesity Treatment Response Variability in Humans: Methods and Illustrations” was published in a recent issue of Human Heredity.