Since you opened a new thread about it I thought I'd copy the link I posted on another thread about food. Our vet also says there's nothing wrong with grains and that a lot of time grain free prescribred/suggested for no reason.
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I found a link with all of the complaints submitted from dog owners to FDA before and after their report in 2018 was published. For those concerned about this topic I think it's worth checking if the food we feed came up in complaints.
Also, out of hundreds complains only 5 of them are yorkies.
https://www.fda.gov/media/128303/download