This article is from the Solid Food for Infants FAQ, by David M. Poduska poduska@cis.ohio-state.edu with numerous contributions by others.
An interesting point is that cow's milk antigens can reach an entirely
breastfed infant if its mother consumes dairy products AND has what is
known as a 'leaky' gut, which passes whole proteins into her bloodstream.
About half of cases of colic may be resolved if the mother cuts out dairy
products altogether from her diet. If you wish to test this, wait at
least a week after going off dairy products to assess the results, as
that's how long it can take for the diary proteins to be cleared from the
mother's system. Parents whose children's colic cleared up when the
mother gave up dairy products may wish to be particularly careful in
introducing dairy products to the child's diet later on, and may even
wish to reduce exposure to dairy products during future pregnancies, as
the colicky infant's sensitivity to dairy products is developed in the
womb.
 
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