Should I lose 20lbs first and then do lower lids? Does it have an impact on the outcome?

Weight loss or gain should not alter your lower eyelid puffiness or fat. It is fine to go ahead with your lower eyelid blepharoplasty and should have not effect your outcome. Good luck with your procedure.

Weight loss and gain should affect the surgical procedure (lower blepharoplasty) or outcome so you are okay to proceed. Due note that weight loss in general causes the face/eyes to look more aged but that doesn't mean you shouldn't lose weight.

Thanks for sharing.  Significant weight loss after certain facial rejuvenation procedures may have a negative impact. That said, a potential 20 lb weight loss after a standard lower (or upper)  blepharoplasty should have not real impact on your results.  Best of luck!

Losing the weight should not affect the surgery.  IT would be very rare for 20 lbs to change the amount of fat in the lower lids. 

  A 20 pound weight loss will have no bearing on the lower lids, since the fatty deposits  are not weight dependent. It is okay to proceed to do the lower lids before or after a 20 pound weight loss