I don't have any references on this as I am at home.  On most high protein,
low carbohydrate regimens the concerns include (1) increased uric acid
formation which can precipitate gout attacks in susceptible individuals and
(2) ketosis.  I don't know how much of the ketones pass from the blood to the
mother's breastmilk, but I do know at the Diabetes Center where I work when we
work with women have gestational diabetes (or diabetes mellitus type 1 or type
2 who are pregnant), we provide at least 200 grams carbohydrate  per day and
monitor urine daily for ketone production because ketones are "bad" for
developing babies in utero.  I'm not sure of the effect of ketones, but if I
recall correctly, I think there is concern about brain development.

Kathy Vannoy MS RD LD CDE