I'm not sure I read the first post on this but I gathered a 4 month old boy
weighting 20 lb?  As others have posted, there is very little link between
obesity in infancy and adult obesity.  It's when they get to be older
children and teenagers that the association is great.
At any rate, I think it is important not to assume that since he is being fed
the appropriate food (breastmilk), that he is also necessarily being fed the
appropriate way (on demand).
While a "diet" or milk restriction, solids, etc. are clearly not necessary,
it may be a good time to make sure mom is picking up well on baby's signals
of hunger and fullness.  Is she feeding automatically or is she also trying
other calming techniques (rocking, wearing baby, etc)?  Is she concerned that
baby suck for a certain amount of time or doesn't feel that he's had enough?
 Does a chubby baby equal a healthy baby for her?

Someone asked about Tiny Tummies.  Thanks for asking!  It is a nutrition
newsletter for parents and children.  I focus on nutrition from pregnancy
through teens, with emphasis on healthy eating and lifestyles for the whole
family.  The newsletter includes articles, recipes (mostly vegetarian),
current pediatric nutrition information, Nutrient of the Month, healthy
lunches, etc.  Email me if you would like more information.
 [log in to unmask]  Also, I always welcome "news" on breastfeeding so please
send me anything you think would be of interest.
Sanna James, M.S., R.D.
Editor, Tiny Tummies Nutrition News
Mill Valley CA