You can eat for mass and at the same time gain lean muscle. It's just a little harder because carbs have a lot more calories than protein. Just stay away from sugary carbs, fast food and shovel as much chicken, fish, tuna and egg whites in you mouth as much as possible. An awesome breakfast i have is 3 packs of oatmeal and I cook 6 egg whites and chop it up and mix it in with my oatmeal. Tastes awesome, get my carbs and protein at the same time, plus the carbs in the morning kick start my day.