Genetic Influences on Executive Function and Self-Regulation of Body Mass Index

Abstract

The purpose of this cross-sectional, correlational study was to test a bio behavioral model that proposes self-regulation affects body mass index (BMI) and executive function (EF) mediates the relationship between self-regulation and BMI in a sample of female monozygotic (MZ) and dizygotic (DZ) twins age 25-64 (N=120). The model also suggests that genes influence EF. EF was measured with the TEXAS (a telephone administered measure of global EF) and the Barratt Impulsiveness Scale (BIS11). Self-regulation was measured with the Goal Systems Assessment Battery (GSAB), a self-report item with nine subscales representing different aspects of Self-regulation. BMI was collected by self-report. Generalized estimating equations (GEE) were used to adjust for the dependence among the twin pairs. Results showed that Self-Regulation was not associated with BMI, nor was EF associated with BMI, although the association between the TEXAS and BMI trended toward significance (r = .17, p = .062). To examine the genetic influence on EF, a smaller sample was used, comprised only of the twin pairs (N=68, 34 pairs, 20 MZ pairs and 14 DZ pairs) and differences between MZ and DZ twins pairs were compared. The MZ (median 0.76) twins had an 18.3% lower median difference on the composite EF score than the DZ twins (median 0.93), but the Mann Whitney test was non-significant (p = .204). It is not known whether this result is due to the small sample size or reflects no difference between the MZ and DZ twins. Exploratory findings showed that four of the individual subscales of the GSAB correlated with BMI including Self Efficacy (r = -.305, p<.001), Planning/Stimulus Control (r = -.193, p<.05), Negative Affect (r = .230, p<.05), and Self-Criticism (r = .230, p<.05). Two of the individual subscales of the GSAB were associated with the BIS11: Social (r = .186, p<.05) and Negative Affect (r = .331, p<.000) and two were associated with the composite EF score. The Center for Epidemiologic Studies Depression-Revised (CESD-R) was associated with both the composite EF score (r = .232, p<.05) and the TEXAS (r = .201, p<.05), and was associated with four of the subscales of the GSAB: Planning Stimulus Control (r = -.262, p<.01), Self Criticism (r = .488, p<.000), Positive Affect (r = -.309, p<.01) and Negative Affect (r = .496, p<.001). A linear regression model entering all nine of the Self-regulation subscales as predictors of BMI showed that the subscale Positive Affect contributed the most to the model (β= .455, p<.01), with Directive Self Efficacy (β= -2.73, p<.01) and Planning/Stimulus Control (β= -.322, p<.05) also significant. The remaining subscales were not significant. Future studies should use a larger sample size and participants known to be actively working on weight control goals.