If you eat nothing but fruit and grain, you may be missing some protein from your diet. Protein is very good for building muscle. I've also noticed that people that don't eat some kind of meat seem to be more sickly and weak(no offense to any vegetarians). You need fiber in your diet to help keep things moving. Fruits and veggies give you many essential nutrients. I wouldn't reccomend cutting out meat entirely, but you shouldn't eat too much meat. Unless you do it for religious reasons.