Hi there-
It is very difficult to answer your question without more detail...
Losing a small amount of weight before surgery should not affect the operation or outcome...
Losing a larger amount, particularly if the weight loss results in a change in your breasts, with loss of volume and skin sagging, may change your operative plan and should definitely be reviewed with your surgeon if surgery is already planned.
If you are asking whether you can lose weight before consulting with surgeons, then the answer is that, yes- you can- but I never like to hear that patients are losing weight IN ORDER to have cosmetic surgery. If you are losing weight as part of a healthy lifestyle that you are committed to maintaining over the long term and realistically believe that you will be able to adhere to it, then go for it. If you are losing the weight because you think you have to in order to have surgery, but in your heart believe that the odds of keeping the weight off after surgery are low, you need to talk to your surgeon.