I'm assuming that the doc needs you to lose fat rather than weight? If so, there's no reason you can't carry on eating a reasonable amount. You need the energy for work and for biking. You just need to cut out the crap food and drink. It requires some effort, thought and planning. But isn't too hard. I put on about 20lbs of weight in the process of losing fat. Muscle weight isn't a health/medical problem (though it still makes going up hills a PITA!). You might find that this approach works as your work is basically weight-lifting.