I am slightly over weight, although at my worst I weighed 305 lbs, I'm down around 210 now, after three years of eatign right and working out. My UC was dx 10 months ago, but I don't believe it has caused any significant weight loss. Since symptoms crept up last Summer I've lost 14 lbs, but I work out 5-6 times a week, and eat relatively healthy.
I do believe that even though I hit the bathroom multiple times a day, the reason I haven't seen a huge weight loss is I am always eating. I eat close to 3000 calories a day, regardless if I am flaring or not. I know I lot of people avoid food when flaring, afraid of being sick, but for me I watched my brother(who has chrons) lose 80 lbs, because he refused to eat. He didn't look good, and lost so much muscle, and I refuse to allow that to happen to me. So regardless of flare or not I eat, I'd rather be eating, and deal with the UC symptoms, then startving and still deal with those same symptoms.
I due think its possible to maintain your weight with UC, you just have to eat, and eat a lot.