Should You Pre-Chew Your Baby's Food?

Why Alicia Silverstone may say ‘I told you so’

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A lot of what passes as gospel when it comes to childhood feeding practices in America is backed more by cultural norm than by actual scientific evidence. For example, I've previously written about introducing allergens to infants and examined how emerging scientific evidence suggests that the age-old conventional wisdom of delaying introduction of food allergies for the purpose of preventing food allergy may actually increase the risk of a child developing food allergy. It is possible – and even likely – that in a few short years, early introduction of food allergens will become the new standard of practice in pediatrics.

Just as introduction of food allergens before 12 months of age once seemed unconventional to most people – and even radical or irresponsible to some others – there are other childhood feeding practices that draw widespread critique from the mainstream. But as scientific research starts trickling in that vindicates some of these practices, I can't help but wonder if another revolution in childhood nutrition isn't already in the making.

[See How to Breast-feed Twins.]

Take, for example, premasticating infant food. Premastication is a fancy way of saying "pre-chewing," and it involves exactly that: A parent chews solid food to break it down for an infant or toddler before transferring it to his or her mouth. Hollywood actress Alicia Silverstone drew lots of negative attention when she posted an online video of herself doing it for her then 10-month old son. But just because this practice may offend our collective sense of decorum or defy our germ-phobic tendencies, that doesn't mean it couldn't possibly be beneficial.

Think about it: How did parents feed their toddlers solid foods in the millennia of human existence before the Cuisinart was invented? Just like scores of animal and bird mommies, human mommies have been premasticating their babies' food for the greater portion of human existence – and they still do so in many parts of the non-Western world. Indeed, emerging evidence suggests the practice may offer some of the same immune-enhancing benefits as breast-feeding, though the mechanism by which it may do so has yet to be fully understood.

A recent European study shows how saliva transfer from parents – such as would be expected to occur from premasticating food – might possibly translate into tangible health benefits for babies. It found that 18-month old babies whose moms cleaned dropped pacifiers by sucking on them (at least occasionally) were 12 percent and 37 percent less likely to have developed asthma and eczema, respectively, compared to babies whose moms dunked the pacifiers in boiling water or rinsed them. The protective effect against eczema persisted at age 3, and was even stronger for babies who were also delivered vaginally (as opposed to via C-section). The study's authors hypothesize that the observed benefits could result from a transfer of beneficial bacteria from the mothers' saliva that then populate baby's gut and promote normal immune development.

Critics of the study have pointed out that saliva cannot conclusively be credited with this protective benefit – as pacifier-sucking moms may also engage in other parenting practices that influence their children's microbial exposures. Indeed, the same species of beneficial gut bacteria tend not to inhabit the mouth or saliva, rendering transfer of "probiotic" bacteria from mom's saliva to baby's gut a less likely explanation for the observed immune benefit. (Saliva contains an antimicrobial enzyme called lysozyme that generally incapacitates these types of bacteria.)

Here's an alternative hypothesis: What if, perhaps, pacifier sucking is less effective at cleaning dirt from a pacifier than, say, dunking a pacifier in boiling water? If so, babies receiving dropped pacifiers that were only superficially cleaned by sucking might be exposed to more microbes from the ground – and this microbial exposure is what might be responsible for teaching tolerance to the babies' developing immune systems.

[See Tending your Inner Ecosystem.]

Yet others argue that parental saliva does appear to confer an immune benefit to babies, but not necessarily as the result of friendly gut bacteria. In his book, "An Epidemic of Absence," Moises Velasquez-Manoff contends that early exposure to a saliva-borne virus called Epstein-Barr Virus (EBV) may hold the key to normal immune system development.

In older children, teens and adults, EBV infection causes "mono" (infectious mononucleosis) – the so-called "kissing disease." But EBV is often asymptomatic when contracted by babies – or it may simply result in one of the generic runny nose/low-grade fever episodes that characterize a normal winter season.

Historically, Velasquez-Manoff explains, the transfer of saliva from parents to infants was a key mechanism for exposing young babies to EBV during the optimal window of immunological tolerance: that is, before age 2. Examining a body of scientific research that investigated age of exposure to EBV compared to risk of developing allergy and certain autoimmune diseases later in life, he explains that exposure to EBV after age 2 is associated with a substantially increased risk of developing both allergies and certain autoimmune diseases – compared to exposure before age 2.

[See Do You Really Have Allergies?]

The disappearance of premastication as a feeding practice during weaning, he suggests, may be partially responsible for the later age of EBV exposure in Western countries compared to historical norms. In turn, this later exposure to the EBV virus could play a central role in the increasing prevalence of childhood food allergies and more serious adult-onset autoimmune diseases – like multiple sclerosis, rheumatoid arthritis and systemic lupus erythematosus.

To be sure, the scientific literature on benefits of premastication in the Western world – particularly as it pertains to allergy and autoimmune disease risk – remains in its infancy (no pun intended). Dentists often argue that parents with severe gingivitis or periodontal disease should not premasticate baby's food, as the risk of passing along harmful oral bacteria is high. Concerns have also been raised in the literature about the possibility of transmitting HIV or hepatitis B via premastication. More evidence is needed to sort out whether premasticating infant food deserves to become the norm (again), and whether its benefits outweigh these possible risks.

In the interim, however, I wouldn't dismiss those parents who practice premastication as eccentric or foolish: It's entirely plausible that this unconventional practice may turn out to be a free, simple and effective preventive measure against food allergy, asthma and/or certain autoimmune diseases. If it does, Alicia Silverstone will have earned herself a huge "I told you so."

[See Why These Famous Vegetarians and Vegans Pass on Meat.]

Hungry for more? Write to eatandrun@usnews.com with your questions, concerns, and feedback.

Tamara Duker Freuman, MS, RD, CDN, is a NYC-based registered dietitian whose clinical practice specializes in digestive disorders, Celiac Disease, and food intolerances. Her personal blog, www.tamaraduker.com, focuses on healthy eating and gluten-free living.

Corrected on 05/22/2013: A previous version of this story misstated a comparison.