Comment by Brian T. Steffen

The discrepancy between the positive observational associations and the null genetic findings likely reflects residual confounding in the observational models. Specifically, participants with higher C15:0 levels had healthier cardiometabolic profiles—lower waist circumference, lower diabetes prevalence, lower proportions of smokers, and lower fasting glucose (Table 1). Despite statistical adjustment, residual and unmeasured confounding of this type is difficult to eliminate in nutritional epidemiology.