Okay, so to ammend my last statement, I didn't know you were a buck 60. I made those statements assuming that you were much more developed as a bodybuilder. You know what they say about assumptions...
Unless you are really short, you probably aren't yet at a tremendous level of muscular adaptation; that is, almost no one's genetic potential as a natty bb'r ends at 160. You still have a lot of potential muscle and strength growth before you hit a big wall. This changes things a bit from what I said previously.
I would still recommend an intense, yet minimal lifting program but you will not likely see fast losses in muscle mass and strength if you swap to mma because you are not in a position in which you are carrying excessive levels of lean mass or strength (levels that exceed the needs of mma).
At 160lbs, you could likely continue to add mass and strength, at least for a while, while training for mma pending an appropriate training and nutrition protocol. Your gains would definitely be slower but this does not negate them entirely.
It is worth mentioning that the bigger the lifter, the more tissue which must be repaired after training and the greater the systemic stimulus of the training (due to the larger weights they are capable of lifting). This means that smaller people are capable of lifting heavy weights (respectively) and being recovered in time to take part in their mma training.
Of course, there are many variables to be considered but at your current size losing mass shouldn't be a big worry.
Sorry I rambled on. I am drunk.
Edit: After re-reading Robert's post I realized that I just repeated everything that he said in different words. This is proof that great minds think alike