Grew up never really thinking about nutrition at all. I honestly never put any thought into what I put in me. Used to play video games and drink 2 liters of pepsi or whatever. There was a realization when I went on to college that I wasn't eating properly. My knees were killing me at 22 years old "didn't start college till 22". It wasn't something that happened immediately honestly. I had the help of ephedra early on. I say that helped me alot because my stomach was physically hungry eating what I was supposed to eat per day, so I had to kill my appetite. I eventually started implementing cardio, but honestly early on, the diet had to be adjusted. When I gave up soda, I think I lost 15lbs on that alone. That was a hard break going from soda to diet soda, and now rarely even diet soda.
Starting cardio, I did it by walking first. Eventually as the weight came off, my knees didn't hurt as much and I could start running. I would usually run for specific amounts of time, say 30 seconds, and work my way up to where I could run distances. When I lived on campus at school, probably one of the best things for me was the gym they had there. I was almost instantly addicted to it, hell I was overtraining at one point 5-6 days a week, separate isolated training every day. Bench got up to 255 at one point too.
I will say I haven't had my pitfalls, though I've never gone back near what I used to weigh, worst I've weighed was maybe 230. Thing is, I don't eat fast food anymore, so its hard for me to even eat it without feeling physically sick. Cooking when I grew up helps me now. I honestly blame the 300lbs on general miseducation, I really didn't know how unhealthy things were for me,and when I educated myself on food and nutrition, I learned how to control it and get it to work for me.