My puppy also eats a lot of grass. In fact I can't keep it out of his mouth. I had to start bagging the clippings after I mowed. I feed a Chicken and potato formula food so I don't think its the food you feed. I'm chalking it up to just being a puppy. On numerous occasions I've found Hans just ripping the grass up not actually eating it.
"The more people I meet, the more I like my dog"