We had dieticians monitoring our intakes. We had special exceptions to eat in class, so that we could eat enough to maintain weight. Our coach was an Olympic medalist and trained all of us like he expected the same from us. I made first runner up for the national team my freshman year of college, but then focused on other things. Once I knew it was possible, an Olympic medal didn't seem worth the effort.

The main thing that is great about swimming long distance, as opposed to running, is that swimming is almost 0 impact. The other benefit is that you'll start burning fat quicker, because your metabolism has to kick into overdrive, as the water is leeching heat from you as quickly as it can.