I'm 40, I am very fit, I do triathlons, lots of swimming, weights, soft sand running, cycling, boxing, basically anything to keep fit.
I have about 6% body fat, and was weighing just over 200lbs.
During my last big flare up I lost 44 lbs in six weeks!!! I looked like a skeleton ... it was awful, I didn't want to leave the house, I went from 200 lbs to 156 lbs, I'm now weigh 187lbs.
Once the flare up ended I put the weight back on really quickly, probably within 2 months.