I did a little running before surgery and had trained some with a couch to 5k program. I started back with it about 6 weeks post-op. and ran my first 5k at 3 months out. I've done 3 more since (I am 6 months post now). I like that distance for now but may increase in the future. For me, being able to drink only small amounts only lasted a short time after surgery. Drinking is different than eating solid food. Immediately post op it was difficult to drink or eat more than 1-2 ounces over 30 minutes and I still can't eat more than say 3 ounces of meat and a few ounces veggie or other side at a time. But drinking 16-24 ounces of liquid over 20-30 minutes is no problem for me now, if there's no food in my stomach. I try to stick to stopping drinking 30 minutes before meals (the hard part for me)and waiting 30 minutes after (not a problem because I am full). Before running, I eat a small meal, a little more carb than I usually would. I don't have any problem grabbing a drink along the race route or drinking a 16 ounce bottle of water over 10-15 minutes after a race. This has been my experience so far, I think even training for/running a marathon is very do-able with a small stomach without becoming dehydrated. Hope this helps!

I'm several years out, and I can drink enough water to stay hydrated while running in the heat or working out intensely at the gym. After the initial post-op healing period, I've never struggled to get fluids down. I don't see any reason you couldn't train for a marathon.