exercise routine, fasting will likely help you maintain your muscle mass while burning fat.
When you fast, your body ramps up the HGH production, which helps you maintain muscle. Once the glycogen stores in the liver are depleted (during a fast), your body switches to burning fat while leaving the muscle alone.
I've been having really good success with losing fat and maintaining muscle through fasting.
I don't have the references for those studies handy, but could get then this evening if you are interested.