I was an All-State swimmer and three time conference champion in the 50 yard freestyle when I was in high school. I was the exact same height as I am today (5' 11") and only 150 pounds my senior year during swim season. I was even less my junior, sophmore and freshmen years but never below the low 140s. I was thin, lean and "toned." However, I was swimming 30,000 to 45,000 yards per week, nearly all year round. In other words, I was burning a LOT of calories. Possibly 10,000 calories per week just from swimming. I often would eat two dinners and still could not gain any weight. The moment I went off to college and stopped swimming, I piled on the pounds. I kept eating the same, if not more so naturally I went from a caloric deficit to a surplus. Within 18 months I was up to 218 pounds! That was 13 years ago and I've been fighting my weight ever since. Matter of fact, I have never been below 192 since. So sure, like Steve said, if you're burning more than you are taking in, you'll lose fat and eventually get lean. Good luck. Swimming is awesome and I often dream of competing again.