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Should You Chew Your Child’s Food?

By now, you’ve probably seen the Alicia Silverstone pre-mastication video [7]. It’s totally safe for work (maybe not for lunch, but your mileage may vary), but some viewers will find it a bit unsettling: Silverstone feeds her baby pre-chewed food directly from her mouth, just like a bird. I found it pretty fascinating and not at all upsetting. Before you recoil in disgust and/or horror, think about how people weaned babies before Magic Bullets, Vitamixes, Gerber baby food, and even mortar and pestles hit the scene. That’s right – they chewed their food for them. In a paper entitled “Premastication: the second arm of infant and young child feeding for health and survival,” Gretel Pelto speculates that pre-mastication was likely common practice among pre-agricultural groups and confirms that it continues today across every continent (PDF [8]).

As to why this practice arose in humans but not other mammals, it’s the neoteny [9]. Humans are born completely helpless, and remain so for several years (some would suggest “decades”). Newborn babies have no teeth and don’t even develop a decent set until about a year or later. This isn’t an issue at first, since they have access to plenty of delicious, nutritious breastmilk that goes down smooth. But because breastmilk is fairly low in iron [10] (albeit a highly bioavailable form designed specially for infants), once kids run out of their pregnancy iron [11] stores, they need a more reliable source of the mineral in addition to the milk [12]. Nowadays, kids get iron-fortified rice [13] cereal or baby vitamins or something silly like that, but before all that stuff, kids needed to eat iron-rich foods when the iron supply dwindled. What’s simpler and more effective for a hard-working hunter-gatherer who needs to feed her child some adult, iron-rich food – chopping up and crushing a strip of venison liver [14] on a wooden plank with stone knives, or chewing it up and transferring it directly to the kid’s waiting mouth?

Okay, so there’s historical and evolutionary precedent for it, but is there any reason to chew your kid’s food today rather than whip out the food processor? Are there any extra upsides?

Free Mechanical Digestion

Since babies are rather limited in the tooth department, they can’t chew their food effectively, which is how most animals – humans included – mechanically digest their food. That’s why “baby food” is pureed; it’s a more socially acceptable (and financially lucrative) way of pre-chewing their food for them. And since the greater surface area of mechanically digested food bits exposes more of them to enzymatic action, pre-chewed food is more easily digested by babies (and adults).

Chewing your kid’s food is definitely cheaper than buying baby food, and it’s more time-efficient than making it in a blender or food processor.

Oral Enzymatic Pre-Digestion

Infants are born equipped with the enzymatic machinery to handle the simple sugars [15], animal fats [16], and animal protein in breast milk. They are not ready to digest a whole lot of other things, particularly dietary starch (which is often “baby’s first food” regardless). In humans who have it, salivary amylase predigests starch during the chewing process, initiating the conversion of starch into more easily assimilable carbohydrate derivatives like maltose (a disaccharide of two glucose units) and dextrin (a polysaccharide). Infants don’t come equipped with much salivary amylase right out of the box, so when a parent who wields the full array of salivary enzymes pre-masticates their food, the infant digests the food better. To get an idea of what kind of enzymatic digestion this pre-mastication is providing, let’s check the numbers:

In adults, salivary amylase (which predigests starch) is present in concentrations of 70-300 U/ml. Infants are born with “negligible” amounts, attain “appreciable levels” by 3 months, and reach 85% of adult salivary amylase levels by five months (PDF [17]). Since Alicia Silverstone feeds her kid a vegan diet [18], presumably rich in fruits and starches, pre-mastication is a sound tactic.

There’s also lingual lipase, which breaks down long-chain triglycerides into glycerides and free fatty acids. Infants have lingual lipase at birth, but they have very little gastric (gut) lipase. Since babies absorb far less dietary fat than adults (65-80% versus more than 95%), a little extra lingual lipase activity provided by the pre-masticating parent combined with the kid’s lingual lipase could improve absorption rates [19]. Hey, maybe that’s what’s causing infant obesity – a wave of pre-mastication sweeping the nation!

Unless you’re drooling into your Vitamix, the parent who pre-masticates may be giving her kid a digestive advantage.

Transplantation of “Good” Oral Bacteria

Over 700 species of oral bacteria have been identified from human mouths, and the oral microbiome of any given individual may house from 30 to more than 100 different species. While oral bacteria can trigger the development of dental caries and periodontal disease, it’s not all “bad.”  For example, many strains of oral bacteria taken from healthy children actually provide protection against harmful oral pathogens [20] and are being developed as oral probiotics. Other strains have been shown to directly influence the immune response in gum tissues [21], as well as protect the host from oral pathogen-induced apoptosis and inflammation [22].

I wasn’t able to pull up any explicit references to pre-mastication as a transplantation method for “good” bacteria, but there is evidence that mouth to mouth contact between mother/father and offspring can transfer pathogenic cavity-causing bacteria to the child [23]. If the “bad” can be transferred, why not the “good”?

Development of the Immune System

Saliva contains the very same antibodies found in breastmilk, like immunoglobulin A, immunoglobulin G, and immunoglobulin M. These help establish the budding immune system and provide passive resistance to pathogens, including bacterial infections and viral infections. There’s very little research on the impact of saliva-borne immunoglobulins on infant health, but we do know that breastmilk-borne immunoglobulins are crucial to the development of an infant’s immune system [24], so it seems likely that pre-mastication is also helpful (especially since both breastmilk and pre-chewed food enter a child through the same orifice).

Perhaps it’s even a way for non-breastfeeding mothers to give their child a leg up.

Are there any downsides?

Transfer of “Bad” Oral Bacteria

As I just mentioned, a parent with dental disease [25] caused by bacteria could transfer the same bacteria to their child by pre-chewing his food. If the bacteria takes hold early enough, it could be difficult to dislodge it. The same could just as easily be said for the early transfer of good bacteria, though, so it’s impossible to say who “wins.”

It all depends on the oral health of the pre-masticator.

Transfer of Saliva-Borne Disease

Transfer of saliva-borne diseases is a possibility. Those include hepatitis G, herpes, TT-virus (which is widespread and seems pretty harmless), hepatitis B (although the hepatitises are present in low amounts in saliva), and there’s mixed evidence that pre-mastication can and has transferred HIV from caregiver to child [26], although that probably requires an open sore or wound in the mouth.

Again, it depends on the health of the caregiver.

Pre-mastication appears to be a valid, viable way for Ma (or Pa) to deliver food to a baby’s maw. There are some impressive potential health benefits, it might save money, and it could even bolster immunity. The potential downsides, however, must be considered. Overall, I don’t think it’s necessary for parents, and the social pariahism you’re likely to face may not be worth the trouble, but I certainly find it intriguing.

How about you, folks? Would you – or have you already – pre-chew your kid’s food?