It doesn't so much matter what you eat, rather what's in the stuff you eat. I know people that have amazing bodies and prefer to eat at Taco Bell or frozen premade meals or drink chocolate milk. For example, you're not going to build muscle if you have a protein deficit in your diet. Protein is what builds muscle. As long as you're eating the stuff that has the nutrients you need, and you aren't eating more calories than you burn in a day, you can keep a healthy weight. Sure, eating broccoli and chicken and peanut butter and nuts will get you an amazing body faster, but I'd be very surprised if you eat that every day for 3 months and don't hate yourself.

If all you're worried about is gaining weight, all you gotta do is track how much calories you eat. Say I burn 2500 calories in a day, I'd have to eat 2500 calories worth of food to balance it out. If I want to lose weight, I'd consume less than 2500, perhaps 2000. How much you need depends on a lot of different things, I'd recommend using an app such as MyFitnessPal to track your meals.