Why Am I Five Pounds Heavier?

Ok. In the last 30 days I've ridden my bike 48 hours and 37 minutes. I've covered 828 miles at an average speed of 17 MPH. I've climbed 16,938 feet and burned 75,623 calories. Seems to me I should lose a few pounds. But no. I have gained 5 pounds. I think it might have to do with my new bike. I'm riding faster and farther but my heart rate is lower. In the last seven days my average speed has increased to 18 MPH (5.6%) but my average heart rate has fallen to 123 BPM from 128 BPM (3.9%). My new bike weighs 7.5 pounds less than my old bike. So what has happened is that I have gained part of this weight back because my new bike is easier to ride. I'm just not burning as many calories on my new bike. So, to lose weight I need a heavier bike or I have to bike a little longer (by 5%-10%). After the ride on Tuesday I replaced the seat post that came with my bike with a new Thompson seat post. It's black and made of aluminum and looks good with the bike. It weighs about the same as the original post but is lightly scored to prevent slippage. During the ride I got to talking to a fellow rider named $Bill who had experienced the same slippage problem with his seat post. He recommended the Thompson solution and has been happy with the fix. Tomorrow I'll be testing it with a little longer ride where I can burn a few more calories.