When my son was 6 weeks old, he would cry and cry and cry and cry. Even though I knew, of course, that babies did this—crying is their M.O.—the fact that nothing I did remedied my son’s shrieks and that I couldn’t identify a cause made the scientist in me crazy. There has to be something logical going on here, I would tell myself. Something I can fix.
Several Google searches later, I decided that his wails were my fault: My son, I surmised, was allergic to cow’s milk, and my smoothies and more-than-occasional ice cream indulgences were probably infiltrating my milk and making his tummy hurt. I gave up dairy for a few weeks to see if it would help. And to this day, I have no idea if it did. Sometimes it seemed to; other times it didn’t. Eventually, a piece of pizza called to me, I ate it, my son did OK, and I gave up on my theory.
Parenting forums are teeming with moms discussing their babies’ so-called dairy and soy “sensitivities” (one mom helpfully recommends gummy bears, oreos, and potato chips as dairy-free snacks), and many of my friends swear that after giving up certain foods, their unhappy babies turned into cooers overnight. But anecdotal reports are one thing; what does science have to say? The research on this issue is complex, but the consensus is that, most of the time, a baby’s crying—even when incessant—isn’t caused or exacerbated by what you or he is eating. Babies cry, and it sucks, but it’s normal. Moreover, mothers who give up foods while breast-feeding can put themselves or their children at risk for nutritional deficiencies. That said, a small percentage of babies are indeed allergic to food proteins—somewhere between 2 to 8 percent are allergic to cow’s milk, but among babies who have only ever been fed breast milk, the risk is only about 0.5 percent; an infant’s risk of being allergic to soy is estimated at 0.7 percent—and these babies, who usually have other warning signs in addition to crying a lot, do fare better after dietary changes.
Food allergies and intolerances are notoriously difficult to diagnose in young kids. (An allergy is not the same thing as an intolerance: The former usually involves an immune-mediated reaction, whereas an intolerance can involve different physiological responses, not usually immune.) Some children do not respond to skin prick tests when they are allergic, while others who aren’t allergic do. Blood antibody tests (which look for evidence that the body is primed to react to certain proteins) aren’t always useful either, in part because some food intolerances don’t involve antibodies.
In general, immunologists and allergists believe that the best way to diagnose mild food allergies is through double-blind, placebo-controlled oral food challenges, in which children are exposed to suspected food allergens and to “fake” allergens at alternating times, without knowing which is which, while being closely monitored for symptoms. Diagnosing allergies this way helps to identify the high percentage of kids who seem allergic but really aren’t. When Dutch researchers gave food challenges to 116 infants and toddlers who were suspected of having cow’s milk allergies in a study published in February 2013, they found that only 40 of the kids, or about one-third, were truly allergic. To further complicate things, childhood allergies are often short-lived, so tests aren’t always consistent. (This is true of cow’s milk allergies, which most children outgrow by age 3.)
And true food allergy or intolerance “symptoms” involve far more than just crying. “If a baby really does have an allergy to something that was in the mother's milk, there would be a broad spectrum of symptoms,” explains Jane Heinig, director of the Human Lactation Center at the University of California–Davis. These include breaking out in hives or an eczema-like rash, having mucusy or bloody diarrhea, coughing and/or vomiting. So if your baby is crying and spitting up a bit after a meal, but nothing else, there’s probably no allergy or intolerance. (If you do see these symptoms, then yes, your baby could be allergic, and you should take her to a physician to help identify the triggers. Or she could be lactose intolerant, but this problem is, again, rare in children under the age of 2.)
If food allergies are so rare in babies, why do so many breast-feeding moms cut out foods? Well, for one thing, the foods you eat can give little Lena gas, just like they give you gas, and this can make her grumpy. One survey-based study found that nursing mothers who reported eating cabbage, broccoli, cow’s milk, onions, or chocolate were more likely to also report irritability and crying in their infants. But a little gas doesn’t mean you should limit your diet. Breast-feeding moms need lots of nutrients, and it’s harder to get them on restricted diets, especially if mothers have eliminated nutrient-rich food groups like dairy. Plus, “being exposed to different foods is a really good thing for a baby,” in part because it helps introduce and prime them to like important flavors, says Diane Spatz, director of the lactation program at the Children's Hospital of Philadelphia—and this achievement is probably worth more than a few smelly farts.