Multiple Modelling Methods Suggest That Grain-Free Diets Are Not Predictive of New Owner-Reported Cardiac Diagnoses Over Two Years in the Dog Aging Project, Despite Owner Misclassification of Diet.

Abstract

Background: Grain-free diets have been potentially linked to dilated cardiomyopathy (DCM) in several studies in dogs, although the underlying mechanisms for this potential link, if present, are unclear. Additionally, some studies have found no association between grain-free diets and DCM in dogs. Unfortunately, many of these studies were limited by the validity of owner-reported diet information. Furthermore, the effect of grain-free diets on other cardiac conditions in dogs is even less studied.

Objectives: To assess the validity of owner-reported grain-free diet status information, and to model the potential effect of grain-free diet exposures over the first several years of Dog Aging Project data collection.

Methods: The validity of owner-reported grain-free status of the diet was evaluated by comparing owner-reported grain-free diet status to the ingredients. Several regression analyses were performed, accounting for likely confounding factors identified with a directed acyclic graph (DAG), to measure the effect of owner-reported grain-free diet status on all cardiac diagnoses. General linear mixed-effects models and general linear regression models were used with similar results.

Results: There was a large misclassification error in the diets reported to be grain-free. In spite of this, modelling methods anticipate that any bias introduced into an effect estimate would be very small. Several modelling methods failed to find a statistically significant association between grain-free status of the diet and any cardiac diagnosis. When including incident-only cases in a linear model with confounders, the odds ratio for the effect of grain-free diet status on any new cardiac diagnosis was 1.05 (0.91-1.21, p value 0.52), suggesting no effect.

Conclusions: The findings suggested that the potential effect of grain-free feeding on all owner-reported new diagnoses of any cardiac disease within this dataset is likely minimal or absent.