If you want to lose weight I suggest riding longer distances.

Last year I started the summer by riding ~20 miles a day. The weight wouldn't budge, so I increased my mileage to 25 with a couple of short hills and started to lose. By October I was riding 5-6 days a week, 35-40 miles a day, with lots of hills and had dropped 20 pounds. I managed to keep the weight off during the winter months (first time ever!!) and am still losing. I've already dropped 5 pounds since the spring training/riding season started.

Try building up to longer distances. It worked for me.

I too have an HRM and use it to monitor my progress. Record your ride information in a training log to keep track of how you are doing and where you need to make changes.