Why have I gained 10 lbs. four weeks after abdominalplasty w/ no liposuction?

Petgriff,
Abdominoplasty will not prevent you from gaining weight. Many persons have problems with maintaining body weight after they lose some of it. You will gain weight if you don't burn calories you take. You can try by increasing level of activity. 
If you have any doubts then you should visit your plastic surgeon.
I hope this was helpful,
Dr. Daniel BarrettPlastic and Reconstructive SurgeryBeverly Hills, CA

Thank you for reaching out. It is very normal to have quite a bit of post op swelling from a tummy tuck. Fluid retention is very normal. I would speak with a doctor about such a low calorie diet, maybe up your calorie intake by a bit and keep in close contact with your surgeon. Some patients have swelling for the first 3-6 months, everyone heals differently and at a different pace. Best of luck! Dr. Kachenmeister

after surgery BUT most of it is fluid weight right after the procedure and the weight comes down quite easily.  If you're gaining weight with 500 calories a day, you should see your surgeon for some advice.  You are on a starvation type diet and that slows your body's metabolism.  Its better to eat more and be more active and at 4 weeks post-op, you should be able to be much more active and you should clear what activities you can do with your surgeon.

Gaining weight after surgery is universal in the temporary phase. One of the body's physiologic responses to surgery is to hold on to fluid. This is a natural and probably important process that resolves typically over the first few days after surgery. With tummy tuck, there is also some chronic swelling in the relocated skin of the front of the abdomen and also any side areas which were treated with liposuction. Watching your nutrition is very important after tummy tuck because excellent nutrition is key for a good recovery/result.  You need to be very selective about the quality of your food because most patients are not able to eat larger portions or exercise as vigorously for a while. I think it is important to know how much tissue was removed and subtract this from your pre surgery weight. This number is your new baseline. Although carefully avoiding weight gain and monitoring your nutrition is very important after tummy tuck, I don't advise patients to weight themselves for several weeks after surgery.