midnight upchucking

Question
I have a big neutered male 4 yr. old choc. lab, and every 5-10 nights about 3am he retches and finally vomits mostly water.  I feed 2 cups of Pedigree morning(about 9am) & night(about 5).  He's always hungry but maintains his weight and seems to be in excellent health.  So what's the deal with the vomiting?  Any suggestions, Labman?

Answer
I think Labs feel they need the body of a seal in case they ever have to retrieve a duck.  So he may be occasionally supplementing his diet with something he forages.  If you have never ask the vet about it, you might the next time you are in for a routine visit.  Otherwise, it is trying to keep him form eating who knows what.  Maybe even limit the water he drinks in the late evening.  

I will mention my friend's Lab that would throw up after eating a stick.