Beer and breast milk

I've just started reading Dombey and Son by Charles Dickens. Like other novels by Dickens - Great Expectations, David Copperfield, The Old Curiosity Shop - it abounds with references to beer and brewing.

As the novel opens, the son of the title has just been born. His mother dies shortly afterwards, leading Mr Dombey to employ a working-class "wet nurse" to breast feed him.  He also orders that she be supplied with "porter - quite unlimited."

I've heard the idea before that stout promotes the production of breast milk.  According to the beer writer Michael Jackson, in Malta Farsons Lacto Stout is prescribed by doctors to breastfeeding mothers. 

The question is whether it's actually true.  Is it an advertising ploy like Guiness is Good for You or is there scientific evidence to back the claim up?