the dancing kitten
in_the_rain
Some babies are actually allergic to their own mother's milk. Other than that, women should breastfeed.
It's not the breatmilk per se that the baby is allergic to, it is what the mother has eaten.
My baby gets sick if I eat red onions or spinach, becuse something in them gets into my breast milk.
Many babies cannot handle processed sugars that a leached into the milk supply. Many others cannot handle cow's milk proteins (casein). Others have problems with garlic or herbal supplements the mother is taking. Peanut butter is another food that can cause sensitivities.
Every doctor I talked to when my son had colic (for the first 10 weeks of his life) said that I needed to eliminate the above. So now I don't take garlic supplements, I don't drink cow's milk, and I don't eat candy - my son hasn't had an episode in nearly 3 weeks.
It is simply the mother's responsibility to eat healthy and to keep the junk food she takes into her body in moderation to fresh fruits and vegetables, natural proteins, and a healthy variety of different foods.