MY DOG SEEMS TO GET A STOMACH ACHE AND DIARRHEA FROM NUTRO PUPPY FOOD, DO YOU THINK IT IS A REACTION TO GRAIN?

I was thinking he may be having an intolerance to grains. He is 11 months and I need to figure out what to feed him for adult food. He seems perfectly healthy most of the time, he just groans when he sleeps sometimes and gets the runs alot. He doesn't have worms or anything like that.