my vet wants me to switch food but im hesitant

My dog is 7 and up until this year has been perfectly healthy. I've fed him Nutro Ultra since he was a puppy.

The past 2 months, he's had some abnormal urine results, first he had crystals, then he had a low negative gravity (?), so they did a blood test and everything came out healthy. We need to repeat it again in a month.

The vet recommends slowly switching him over to Natural Balance or some other grain free food. I guess my thinking is he's been eating the same food for 7 years without much issue, what if something goes terribly wrong by switching him after all this time? He doesn't eat people food (he gets violently ill), he only eats his food and the occasional treat.

What are your thoughts on switching to grain free after all this time? TIA

Re: my vet wants me to switch food but im hesitant

Grain free foods are less allergenic and should not cause your dog any ill effects as long as you transition to the new food slowly.

Re: my vet wants me to switch food but im hesitant

you're most likely right. i spoke with my vet again and he said he has seen instances of dogs getting urinary tract infections after swtiching to grain free food. since we're still waiting for him to have normal urine results, we decided to wait till the summer to switch over. i have to do more research too.