[afroisalreadyin]

There was a time when I got used to eating a big plate of fries with my normal lunch (the student canteen at the university where I studied was just phenomenal), and after a couple of months, I had put on considerable weight. The problem was, I was thin my whole life, and I just couldn't imagine being overweight, so I didn't ever get on a scale, and had no idea how much I had put on. It was my mother telling me "my son, you've become properly fat" that made me realize that something significant had changed. The scale was now showing 90 kg, closer to 100 than my to my normal weight. After a couple of months of eating properly and running, everything was back to normal, but that was a stark reminder of how anyone can become obese given the right (or rather wrong) conditions.

[yodsanklai]

Usually, it happens insidiously. After 30-40, metabolism slows down and it's easy to very slowly gain weight, even for people who didn't have weight issues before. Losing weight can be quite hard. To me the solution is to monitor my weight and avoid junk food as much as possible. I never drink soda, avoid fries. Sometimes you have no choice (e.g. traveling and no easy healthy options), then I try to only eat once or twice a day.