I started commuting in March, biking 5.5 miles each way about the same length your commute will be. I am lucky in that we have a locker room and shower at work, so I push my self a bit and get sweaty. Since I started cycling, my appetite has gone up and I have been eating like a horse but I'm still losing weight. I started at 6' 220 lbs and am now down to 205. I'm expecting to keep losing some pounds because I'm still a bit overweight. Now that I am in better condition I'm thinking about lengthening the bike part of my commute - I currently do a multi-modal commute car-ferry-bike. If I cut the car out entirely I'll be going 14-15 miles each way.