Assessing the causal role of adiposity on disordered eating in childhood, adolescence and adulthood: a Mendelian randomization analysis

Background
Observational studies have found that a higher body mass index (BMI) is associated with an increased risk of developing disordered eating patterns. However, the causal direction of this relationship remains ambiguous.
Objective
Our aim was to use Mendelian randomization (MR) to infer the direction of causality between BMI and disordered eating in childhood, adolescence and adulthood.
Design
MR analyses were conducted using a genetic score as an instrumental variable for BMI to assess the causal effect of BMI at age 7 on disordered eating patterns at age 13 using data from the Avon Longitudinal Study of Parents and Children (ALSPAC, N = 4,473). To examine causality in the reverse direction, MR analyses were used to estimate the effect of the same disordered eating patterns at age 13 on BMI at age 17 using a split-sample approach in ALSPAC. We also investigated the causal direction of association between BMI and eating disorders (EDs) in adults using a two-sample MR approach and publically available GWAS data.
Results
MR results indicated that higher BMI at age 7 likely causes higher levels of binge eating/overeating, weight/shape concern and weight control behaviour patterns in both males and females and food restriction in males at age 13. Furthermore, results suggested that higher levels of binge eating/overeating in males at age 13 likely cause higher BMI at age 17. We found no evidence of causality between BMI and EDs in adulthood in either direction.
Conclusions
This study provided evidence to suggest a causal effect of higher BMI in childhood and increased risk for disordered eating at age 13. Furthermore, higher levels of binge eating/overeating may cause higher BMI in later life. These results encourage exploration of ways to break the causal chain between these complex phenotypes, which could inform and prevent disordered eating problems in adolescence.