Here are parts (quotes) of the article on Kellymom:
A small percentage of breastfeeding mothers notice an obvious difference in their baby's behavior and/or health when they eat certain foods. Cow’s milk products are the most common problem foods and the only foods conclusively linked by research to fussiness/gassiness in babies, but some babies do react to other foods. Food sensitivities in breastfed babies are not nearly as common as many breastfeeding mothers have been led to think, however.
Food reactions may occur within minutes, but symptoms in breastfed babies more commonly show up 4-24 hours after exposure.
Eliminating a food for less than 2-3 weeks may not be effective—cow’s milk protein, for example, can persist in mom’s body for 1½ - 2 weeks, and it may be another 1½ - 2 weeks before the protein is out of baby's system.
(Angela note: I know if a baby is given formula that research shows it takes 2-3 weeks to get it out of the gut.)
Baby’s symptoms will usually begin to improve within 5-7 days of eliminating a problem food. Your baby may not improve immediately, however, especially if the reaction is to a food that has been a regular part of mom's diet. Some babies seem to feel worse for about a week before symptoms begin to improve. Sometimes it takes several weeks to see an improvement.
If you think that your baby may be sensitive to dairy products in your diet, remember that it can take 10 days to 3 weeks to eliminate cow's milk protein from your system--allow a full 2-3 weeks of dairy elimination before evaluating the results.
If your baby is only a little sensitive to dairy proteins, you may be able to relieve baby’s symptoms by eliminating only the obvious sources of dairy (milk, cream, yogurt, butter, cheese, sour cream, ice cream, cottage cheese, etc.); you may even be able to eat small amounts of dairy without it affecting baby.
Jack Newman’s name was also mentioned at the meeting and I like his work and have heard him speak. I researched a bit to see what his comment was about this subject and he suggested taking the milk products out of the diet for 7-10 days.
Lastly this was written by Jan Barger, an IBCLC that is well known and I have heard her speak as well:
….The most likely culprit for your baby is dairy products in your diet — milk, cheese, yogurt, pudding, ice cream, or any food that has milk, milk products, casein, whey, or sodium caseinate in it. Other foods, too — like wheat, corn, fish, eggs, or peanuts — can cause problems. Don't severely limit your diet on the hunch that your baby might have food sensitivity, but if you suspect that a particular food is giving your baby trouble, you could try eliminating it for a week to see what happens. Some foods take longer than a week to completely clear your system, but you should see improvement in your baby's behavior within a few days…..
So after all this research I would conclude that an allergy passed on through the mom’s milk can happen in a small percentage of moms/babies. When it is suspected, taking that food out of the diet for 3-4 weeks would be my recommendation. I would also direct mom to the 3 websites I looked at and/or would type something like this up for her.
I hope you find this information helpful and I look forward to working with you in the future!
Angela E. Swieter, RN, BSN, IBCLC, RLC, ICPE