I feed a higher calorie food than that and my dogs weigh less and I feed 2 cups. You could definitely go higher, just add more food slowly so his body gets a chance to get used to the additional calories, otherwise you’ll be back to the diarrhea. Give him just a quarter cup more for a few days, then a quarter cup more for a few more days, until you are feeding the desired amount. Some dogs are just naturally lean so don’t be surprised if there is only so much and no more that he is willing to eat.
