Acute Renal Failure does have symptoms of less of an appitite, but this does not sound like Acute Renal Failure to me. Acute Renal Failure is when you kidneys shut down. Some symptoms are less urination or no urination and bloody stools. If your dog is not eating, you keep letting it out, and it still drinks water, it is most likely urinating when you let it out. And it sounds like your dogs stools aren't bleeding, but more like it ate something it shouldn't have.
And if the vet said that there was no major damage, why is the dog taking steroids? Personally, I think there is something fishy about that vet. I think you should see another vet to get a second opinion.
You should do some research yourself. I've found a link that would be useful to you.
Click here. Note that this is Acute Renal Failure for Humans.
This one is for dogs. This one also.
But if it is Acute Renal Failure, don't let your dog drink too much! The kidneys must gradually heal.
I really hope this helps