Literature discussed: "Effect of diet change in healthy dogs with subclinical cardiac biomarker or echocardiographic abnormalities” Haimovitz D, Vereb M, Freeman L, Goldberg R, Lessard D, Rush J, Adin D. J Vet Intern Med. 2022 Apr 14. doi: 10.1111/jvim.16416
Key Takeaway: Heart abnormalities in otherwise healthy dogs eating grain-free diets can be resolved/reversed with a change of diet. This is consistent with the findings of multiple previous studies as well as clinical observations.
A recent study (Adin et al.,2021) revealed elevated levels of biomarker cardiac troponin I in healthy dogs eating grain-free diets as compared to dogs eating grain-inclusive diets. This biomarker has been associated with damage to cardiomyocytes, the heart muscle cells. It was proposed that elevations of that marker in dogs eating certain diets may be attributable to low-level cardiac damage. In follow-up of that finding, researchers continued to monitor a subset of cases and measure serial levels of that marker after a diet change. That data has now also been published in a new paper (Haimovitz et al., 2022).
Dogs were included on the basis of their participation in the previous study and the presence of subclinical echocardiographic abnormalities or elevated cardiac troponin I. Diet type was not an exclusion criteria (dogs eating grain free or grain inclusive diets could participate) unless the current diet was one of the six specific formulas offered as an intervention. Study participants had to feed the new, interventional diet for one year and present to the hospital for recheck examinations every 3 months. All interventional diet options were grain-inclusive and did not include pulse legumes or potatoes in the first 25 ingredients.
The final study population included 10 dogs in each diet group. The main significant difference between groups was a lower average weight in the grain-free group, attributable to the inclusion of three small breed dogs (all miniature schnauzers) that were not represented in the grain-inclusive group. At the rechecks, echocardiographic measurements were taken along with physical exam and blood work collection to assess biomarkers.
The study found that cardiac troponin I stayed stable in the grain-inclusive group when diet was changed, but decreased over time in the grain-free group, with the groups having similar measurements from the 6 month mark onward. Dogs in the grain-free group also experienced a significant reduction in left ventricular volume measurement on echocardiogram over time.
Another part of this study was performing a “pulse score” on the diets dogs were originally eating. This was done by assigning a number to pulse ingredients based on their position on the ingredients list, with a higher score corresponding to having more pulses or pulse fractions higher on the ingredients list. Grain-free diets were found to have a higher pulse score (median 52, range 0-80) than grain-inclusive diets (median 0, range 0-72).
The authors discuss that the findings suggest decreased heart muscle damage and improved cardiac performance associated with dietary intervention. It also suggests that the elevated values in the grain-free diet group prior to intervention were likely not a normal baseline for those and instead may be clinically relevant. They highlight that it is unclear what aspect of diet may be relevant to this observation; it could be secondary to the inclusion rate of pulse legumes or other unknown factors associated disproportionately with grain-free type diets.
The authors also discuss study limitations, including a relatively small sample size and limited breed representation. This may have prevented the study from identifying statistical significance where there are actual clinically meaningful differences. An underpowered study can produce statistically significant results if the differences are sufficient, but may miss more subtle differences, due to the way significance is calculated and the impact of sample size on it. In other words, a smaller sample size has to have more dramatic findings in order to suggest that random chance alone did not cause them. They suggest that future research aim to determine what factors of certain diets may influence mild increases in cardiac troponin levels and what impact diet change may have in other breeds or dogs with active heart disease.
My opinion: This study adds to a continuously growing body of literature associating grain-free or pulse-legume-rich diets with cardiac changes in dogs that are reversible with change of diet. While research still needs to discern the underlying mechanism of this association and identify other potential concurrent risk-factors, it is a reasonable approach for prioritizing canine welfare to recommend avoidance of these diets until more information is known.
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