The common problem of college students gaining fifteen pounds (~7kg) during their first year, presumably due to all-you-can-eat dining halls, pizza, beer, perhaps pot (the munchies), and replacement of physical activity with study.

I myself actually lost about 20 pounds in my freshman year of college, probably due to the horrid food in Kagin Commons, my preference for instant miso soup over pizza, and my preference for gin over beer.