The Steiger directionality test supported the hypothesis that the effect of fasting insulin on risk for anorexia is the correct causal direction as the variance explained by the IVs was lower for anorexia than fasting insulin (P = 1.35 × 10−27, P = 1.36 × 10−27 respectively for the upper and lower bound anorexia prevalence estimates) (Supplementary Table 9). The gene discussed is INS; the disease is Anorexia.