You my friend, were one lucky duck. The mission was not so kind to most of us (in that regard-I loved it otherwise). I know for a fact that several of the BYU guys, including some of their former All Americans in track/xc and National Champions in track, gained as much as 30+ pounds and one even got over 200 who later became a multiple time AA.
While those cases are extreme on one end, I think yours is as well on the other. Most probably get something like a few push ups in daily, with a jog at 8-9 min pace for 20 mins twice a week, and a soccer or american football game once a week. I left a 4:10 miler, and returned to run an all out mile in 5:45 a day after coming home. And I mean ALL OUT. Rested up, warmed up, spiked up, high school track with no one in my way at the time, and finished the mile cashed. I thought my running career was done haha.