How important is the diet when it comes to a workout plan?

I read these magazines that have these excellent workout plans. I do the workouts, but I don’t do the crazy diet that they show with it. I don’t eat a lot of egg whites and things like that, but I do make sure I eat healthy and drink protein shakes like Muscle Milk. Is it important to follow the diet plan that they have in these magazines? I mean, prisoners don’t follow a series diet plan and they come out pretty ripped.