Trying to figure out if your breastfed baby is sensitive or allergic to the dairy or soy you’re eating? Cow’s milk protein intolerance (CMPI) is an abnormal response by the body’s immune system to protein found in cow’s milk, which damages the stomach and intestines. Cow’s milk protein intolerance is not lactose intolerance. If you were told it takes 2-3 weeks to clear the dairy from YOUR milk and you should switch to formula in that time, you were given extremely inaccurate (and potentially harmful) advice. 

From freetofeed.com: While more research is still needed, a small study showed lactating mothers who ingested milk prior to being dairy free, found cow’s milk protein peaked at 2 hours post-ingestion and were undetectable at 6 HOURS. While the study was small it was using mass spectrometer ion intensity testing which is incredibly accurate.

Journal of Pediatric Gastroenterology and Nutrition reports “for an immediate reaction the maternal elimination diet needs to be maintained for only 3 to 6 days. If delayed reactions are suspected (eg, allergic proctocolitis), then the diet should be continued for up to 14 days. If there is no improvement, then it is likely that diagnoses other than CMPA are the cause of the symptoms and the child should be further evaluated.”

So while the protein is cleared from your milk in less than a day, the REACTION and damage in your baby’s GI system can absolutely last longer than the protein is in your or baby’s system. It’s the residual inflammation from the protein exposure, not continual exposure from your milk after 12-24 hours that causes the reaction to last for days to weeks. 

If you’re trying ro figure out if baby is sensitive to dairy or soy, eliminate these from your diet but it is SAFE to CONTINUE to breastfeed through the elimination. That protein has cleared from your milk within hours, not weeks.