How long after a breast lift an augmentation can I go on a diet and cut calories to lose a few pounds? (photos)

For the first 2 to 3 weeks it is important that you are taking adequate calories and protein.  I would not diet for at least a couple of months after surgery.

Discuss your intentions to cut your caloric intake with your surgeon. You are only 3 weeks away from surgery and still healing. It seems early to do this and might have an adverse effect on your healing. I would wait an additional 4-6 weeks before beginning your diet. In the meantime, discuss what exercises your surgeon will allow you to perform to help burn off some calories.

It is best not to "diet" after plastic surgery as your body needs the nutrition to heal.  If you are starving yourself, it will affect the results in terms of healing.  I would suggest at least 6-12 weeks before you embark on any type of calorie restriction.  More importantly, I would suggest have a healthy and nutritious diet and get back to exercise as soon as your surgeon says it is ok.  Good Luck