Based on my reading (I'm new to this stuff myself), It all depends on the time you have available prior to your UA. IF you have 3 weeks or more then you should go low fat sweatin' to the oldies until about a week or so before your UA and then switch to High fat w/o exercise.

The low fat, exercise portion increases your metabolism and flushes your fat tissue of THC metabolites...which eventually leave your body via urine. But...you don't want to do that too long because you could end up having more THC metabolites in your urine at the time of the test than if you weren't exercising at all.

You essentially want to strip a much as you can and then add new fat to cover up what's left. I'm sure someone will be able to explain it better than I am.