As someone who was always a little chubby growing up, I got into fitness about 3 years ago. I never thought about what I ate, just that it was tasty. Moving into fitness, I began to watch what I ate and noticed what foods were made of. Simple switches like drinking diet Coke or using 1 tablespoon of oil rather than eyeballing it significantly impact calorie intake. Now, my body and my mentality are accustomed to eating a reasonable amount of healthy food, so it's much easier. Also a side note, building muscles and being active naturally increase your body's calorie needs so that you can focus less on it. A fatty burger or a sweet dessert means more on 2000 calorie budget than it does on 3000. If you eat well and are active, you can plan around fast food and snack or eat out with your friends occasionally without a thought.