James- You can do it! Believe me, if I can find a somewhat reasonable diet and exercise plan to stick to and lose weight (while still on corticosteroids!), so can you!
As you know, what I eat greatly affects my disease so I can't do some things a lot of other people can do. I already can't eat dairy, raw fruits and veggies, many cooked veggies because they have skins or shells on them and I can't digest them, pork, or red meat. Turkey is notorious for making you gassy, and the last thing anyone with IBD needs is more gas!

So, I have...well... chicken, potatoes, rice, and Ensure. I can't stand the taste of fish and I'm allergic to shellfish. I do take Omega-3/Omega-6 pills twice a day to make up for that.
You'll find something that works, I promise! Drink lots of water, take the stairs instead of the elevator, park further from the entrance to the store than you normally would. Every little bit helps!
ETA: or you could just get IBD. It's the best weight loss plan around. I lost 25 pounds in a week! Our support group motto is "Losin Weight Without Speed (or Sunflower Seeds!)"