Ah. The chicken and egg dilemma. 
Many women with large breasts are overweight.
Many overweight women have large breasts.
When you are overweight insurance will tell you your breasts are large because you are fat. Lose the weight and your breasts will get smaller. This is true. Especially as you age, breasts get fattier. Even women who when younger had “breasts which did not change with weight,” will see breast size change with weight change when they are older.
So. You are overweight and have large breasts. What to do?
Back to the chicken and egg dilemma…
If you are overweight you need to work out to lose weight. If you have large breasts, it is difficult to do the aforementioned exercise to lose weight because you can’t run, do aerobics, or do anything else which is bouncy. (Who can find a bra? Must you wear two bras?) Yes, yes. It is not impossible. You can work out with less bouncy things like swimming and biking. And yes, you can lose weight by watching what you eat. But it is more difficult.
Why try to lose weight before breast reduction?
The reasons are multiple:
1. Breasts are about proportion to your body. I don’t know what size to make you if I don’t know what size your body will be.
2. A breast reduction lifts the breast. If you lose weight after your reduction you will loosen up your lift. (This is not good. It will make you droop.)
3. If I make your breasts a perfect size and you lose weight, your breasts will get smaller. Again, it is all about proportion to your body.
4. If you are healthier, you will heal better and faster. There are higher surgical risk and complication rates when overweight, especially if your BMI puts you in the obese category.
So. Get working out. Double bra it and get moving. I love breast reductions and lifts. I think they can be life (and back pain) changing surgery.