If we're talking about weight, it's all about calories in versus calories out. You can eat 2,000 calories of unhealthy foods and gain/maintain/lose the same weight you would if you ate 2,000 calories of healthy foods. While on the scale you may be the same weight, your body will be a mess internally if you just drank coke and ate fast food, which is when nutrients such as protein, fiber, carbs, fats, cholesterol, sugar, etc. come into play.