Just my personal experience.  When I had my first baby I went back to work at
7 weeksPP.  A colleague of mine had a baby a few weeks before me.  we worked
12 hour night shifts together. We took turns during the night with the breast
pump.  We were both ravenous, always checking out the other nursing units in
the middle of the night searching for food because we had already eaten
everything we brought with us.  i was down to my prepregnancy weith 4 weeks
PP.  i gained 28 lbs during pregnancy.  One of the reasons I kept
breastfeeding was because it was the only time I could eat as much as I
wanted and not have to worry about weight gain.  i didn't lose the weight as
quickly the second time around but still had a large appetite and lost some
weight and never gained while nursing.. my colleague alos lost her weight
quickly.  i have had friends who didn't lose much weight until they
weaned...Must be individual differences.