Absolutely. When you lose weight your breasts will reduce in size. Equally if you put on weight your breasts will increase in size.
Good Question.Your breast is made up of breast glands and fat. The fat in your breast will respond to diet and exercise.So, if you lose weight the Fat component of your breast will respond by reducing in size. Whether it will become obvious, will depend on the amount of weight lost and the amount of fat in the breast.