The actress Alicia Silverstone got a lot of grief last week after posting a video to her blog in which she is shown "pre-chewing" her baby's food, and offering it to him straight from her mouth. The "Clueless" star's 10-month-old son, Bear, appears to enjoy being fed like a baby bird. "He literally crawls across the room to attack my mouth if I'm eating," Silverstone blogged.
While most people who commented on the video were quick to voice their disgust and vilify the ill-considered whims of celebrity parents, science suggests that "pre-mastication," or the pre-chewing of adult food for infants, is actually a traditional and healthy feeding method. Standard practice among our blender-lacking ancestors, pre-chewing is still the norm in many non-Western cultures. The act exposes infants to their mothers' saliva, giving them an immune system boost that they can't get from the sterile, pulverized baby food bought in stores.
The benefits of pre-chewing have only recently been investigated, but they appear to parallel those of breast-feeding.
Babies start requiring non-milk food in their diets at six months old, but they don't develop the molars they need to chew most foods until age 18 to 24 months. According to research led by Gretel Pelto, an anthropologist at Cornell University, pre-mastication was the solution to feeding infants during this interim period for most of human history, and remains the method used in many cultures today. Rather than being unhygienic, Pelto and many other scientists think the feeding method carries on the immune-system-building process that begins with breastfeeding. By exposing infants to traces of disease pathogens present in a mother's saliva, it gears up their production of antibodies, teaching their immune systems how to deal with those same pathogens later. [Could Humans Live Without Bacteria?]
It may also prevent the onset of autoimmune diseases, such as asthma, that are very common in industrialized societies. These conditions arise when one's immune system mistakenly attacks one's own cells, and such ailments have been strongly linked to underexposure to diseases during childhood. "The epidemiological evidence [shows there are] increases in asthma and various allergic conditions in children and adults whose environments had significantly reduced pathogen exposure in early life," Pelto told Life's Little Mysteries.
The most common argument against pre-mastication is that infants occasionally catch infectious diseases from the saliva itself. For example, women with HIV are advised against pre-chewing their babies' food. However, research shows that disease transmission through pre-mastication is far less common than was previously assumed, because natural antibodies in saliva significantly reduce the infectiousness of the disease pathogens present there. Research by the immunologist Samuel Baron of the University of Texas Medical Branch has demonstrated that the risk of HIV transmission via saliva is actually very low — lower than the risk of transmission via breast milk.
Breast-feeding was outmoded in the 1950s, and has since seen a renaissance. Silverstone may simply be ahead of the curve regarding pre-mastication. "The evidence for breast milk is overwhelming," Pelto said. We think the story is identical for both breastfeeding and pre-mastication — they save lives by ensuring good nutrition and good development of the immune system. The evidence for pre-mastication has yet to be completed, but the logic is clear and the epidemiological evidence supports it."
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Natalie Wolchover was a staff writer for Live Science from 2010 to 2012 and is currently a senior physics writer and editor for Quanta Magazine. She holds a bachelor's degree in physics from Tufts University and has studied physics at the University of California, Berkeley. Along with the staff of Quanta, Wolchover won the 2022 Pulitzer Prize for explanatory writing for her work on the building of the James Webb Space Telescope. Her work has also appeared in the The Best American Science and Nature Writing and The Best Writing on Mathematics, Nature, The New Yorker and Popular Science. She was the 2016 winner of the Evert Clark/Seth Payne Award, an annual prize for young science journalists, as well as the winner of the 2017 Science Communication Award for the American Institute of Physics.