As usual for me, this is purely anecdotal.  My babies were all girls
and all  8lbs 4oz. at birth (yes...I am nothing if not consistant.)
They all followed the same curve for 15 months, despite very
different nursing patterns.  Big, fat babies with rolls and rolls and
rolls over thier thighs and arms. Termed obese by every Dr. who saw
them.  (except Jack Newman, who said at a conference that my 7 week
old was the breastfeeding poster child)  One was heavy for her age at
 age 4. One was very tiny for her age at 4, and one was the picture
of average.   Who knows?  For the record, I'm 5' tall and a whopping
93 lbs, and except for during pregnancy and the 4 weeks post partum,
I've always weighed that, except as a breastfed baby....when I was
tremendously obese....and strongly resembled Winston Churchill.
Given all this....I don't worry much about obese breastfed babies.

Stephanie Pearl
IBCLC Toronto, Canada