The most recent paper on this topic was published March 17, 2022 in the journal "Frontiers in Animal Science."
It has the same conclusions the FDA report and several other papers have had (despite the misreading of that research by many): There is no credible link between grain-free food and dilated cardiomyopathy in dogs.
In a press release, one of the co-authors of the paper stated:
“Based on the data we received from veterinary cardiologists across the U.S., we did not observe a significant increase in DCM incidence rate over time, which included the recent period when grain-free pet food sales grew exponentially."
“The existing scientific literature indicates that nutritional factors can lead to the development of DCM, but we did not find a correlation in the DCM incidence rate to grain-free pet food sales.”
(Stephanie Clark, Ph.D., CVT, PAS, CFS, Dpl. ACAS, board-certified companion animal nutritionist and co-author of the paper)
Many of the prior studies were flawed and were based on "dirty" data. This study had much better design because it used only cases of DCM diagnosed by veterinary cardiologists. The study sample was also more than adequate: they looked at 68,000 total canine cardiology cases from veterinary cardiology referral hospitals, diagnosed between 2000 and 2019.
The average incidence rate of DCM was 3.9% (ranging from 2.53-5.65%). If grain-free food did in fact cause DCM, we would clearly see a higher incidence rate since such a high percentage of dogs eat grain free. But that was not at all reflected in the data.
The paper acknowledges that there is a trend of increasing DCM diagnoses, however, we need to look elsewhere for the cause as the evidence is repeatedly discrediting the grain-free food hypothesis.
Full paper here: https://www.frontiersin.org/articles/10.3389/fanim.2022.846227/full