Excuse me while I let some steam come out of my ears ..... there, now I
feel a little better.  This guy has slandered you, Denise.  I have dashed
off a few thoughts here, but I will take the time later this week or
weekend to refine my thoughts somewhat, so, FWIW, here are my initial,
red-hot-angry thoughts about what you can do:

First, make sure you have this guy's exact name and title.  Then get the
address of the company for which he works, and his supervisor's name.
Then write a letter.  The following sentences and phrases come to mind:

I have learned that Mr. X has been spreading damaging lies about me to my
professional associates.  He has told people who know me that I reviewed
and approved of  your book.  This is absolutely false.  Your book is full
of out-of-date citations and downright misinformation and is clearly
designed to mislead women away from what I know as  a lactation consultant
is the only optimal means of feeding a baby.

I have consulted an attorney and am seriously considering a slander suit
against Mr. X and your company.  I may reconsider if you (1) send a letter
to everyone to whom Mr. X told this lie explaining that Mr. X was lying
and that I thoroughly DISapprove of your book, (2) publish a statement in
the hospital newsletter detailing Mr. X's wrongdoing and promising never
to do it again.

Rachael Hamlet, the lactating lunatic lawyer mom from HELL