This is an interesting question that I was asked to blog about. There is both a superficial and a deeper answer to this question.
The superficial answer is: it depends on the type of plastic surgery performed and what type of lifestyle changes have occurred.
Certain surgeries are going to be more affected by lifestyle than others. If you have Smartlipo with me (my most popular procedure) and then put on a significant amount of weight afterwards, it will obviously detract from how good you look. You may still get a significant benefit from the Smartlipo because if the Smartlipo brought a better balance to the shape of your body, even if you put on weight, you will likely still have a better overall shape.
A tummy tuck is even less sensitive to minor weight gain, since you will have a much flatter abdomen after a tummy tuck than before. Even if you gain weight, you should still look much better than before surgery. The weight gain, if not too excessive, will generally not lead to loose skin, so the benefits of a tummy tuck will remain. The muscle tightening that is usually done with a tummy tuck will still remain if a few pounds are added after surgery. Of course, if you put on a lot of weight, some of the weight will be belly fat and this could cause your abdomen to protrude.
Procedures such a blepharoplasty or fillers or botox are not going to be affected very much by mild weight gain. Similarly, minor weight gain after a breast reduction will not have much affect.
On a deeper level — and this is where my certified life coaching training comes in — cosmetic procedures can be a stepping stone for transformation. If we look better, we feel better about ourselves. We realize that if we feel better about ourselves, we feel empowered, have more energy, treat those around us better etc. Those of you who have seen me in consultation for a body procedure know that I almost will discuss modification to your diet and exercise. If after doing a tummy tuck or Smartlipo you can be motivated to eat a healthier diet and increase your exercise, these benefits will far surpass anything that i can do for your surgically – especially if you keep those habits for life. So often, I see my patients alter their dieting and exercising and then drop 10-25 pounds, looking and feeling so much better. My concern with putting on weight after a procedure is that the procedure has not fulfilled its potential for being a stepping stone for transformation.