Just popping in to add my two cents...

Def genetics and diet, but two other things to throw into the equation is timing and effort...

If you want to lose weight, you should exercise in the morning (lifts metabolism and it burns more quickly all day)
If you want to build muscle, exercise in the evening, as you rest for 8-12 hours and then another 10-12 maybe before more exercise


Also, effort - watch your heart rate... if it lifts too high on your ride you will not burn fat/lose weight, but you will consolidate muscle mass...


Don't know how these two aspects fit into your regimen, Noushkin.. and others... but the more I cycle, the more of a science I realise cycling is.