It was obvious to her there was no “instinct” pointing blindly to the good and bad in food. The two most popular foods overall in her study were also the sweetest: milk and fruit. Had she offered a choice of sugar and white flour, staples of a 1930s diet, it’s unlikely the children would’ve ended up in such fine fettle. Self-selection, she concluded, would have little or no value if children selected from “inferior foods.”
The real test would be to offer newly weaned infants a choice between natural and processed foods. This would’ve been Davis’ next experiment, but the Depression dashed this prospect, as her funding ran out at the crucial moment. Nonetheless, her experiment left a powerful legacy that took no account of the trick at the heart of it. Doctors, particularly in America, interpreted her experiment to mean that children’s appetites are built-in and benign, without paying attention to the way Davis had changed the babies’ food environment.
Influenced by Davis, the dominant view on appetite among pediatricians became “the wisdom of the body,” which went along with the vogue for child-centered learning. In 2005, pediatrician Benjamin Scheindlin noted Davis’ work contributed to a widespread change in attitudes in pediatric medicine from the 1930s onward. Whereas a previous generation lamented the pickiness of children’s changeable tastes, now doctors positively welcomed childish vagaries of appetite. Many child-rearing experts still think like this, operating on the assumption that children are born with special appetites for exactly the nutrients they most need and that it will all balance out, if only they are given free rein to eat what they like. As recently as 2007, a popular website about feeding children discussed Davis and concluded there was “a strong biological plausibility . . . that children will instinctively choose a balanced diet.”
Beyond the Orphanage
“The wisdom of the body” is an alluring theory. Eating would be such a simple business, if only we had little memos inside our bodies telling us what we needed to eat at each precise moment. (Your vitamin C levels are dropping — quick, eat a kiwi!) The scientific evidence — both from humans and rats — shows the theory is flawed at best. For it to be true, omnivores would need specific appetites for the essential nutrients the body needed at any given time. This is a very unlikely proposition, given the nutrients omnivores need come in so many guises, depending on the environment we happen to live in. An innate appetite for the vitamin C in black currants would be no use if you lived where black currants don’t grow.
In lab conditions, rats — our fellow omnivores — have shown a very erratic ability to self-select the diet that would do them the most nutritional good. Other trials have attempted to find out whether rats could self-select to correct certain vitamin deficiencies and concluded many of them couldn’t. As for human subjects, there is, notes one specialist in the field, no data to suggest innate appetites for specific foods. It does seem possible for humans to learn specific appetites that will correct certain imbalances — particularly a salt craving when lacking in sodium — but that’s a different matter.
Ninety years after Davis’ experiment, the view that food likes are predominantly innate — or genetic — looks shaky. When trying to get to the bottom of where tastes come from, scientists have often turned to twins. If identical twins share more food likes than non-identical twins, the chances are that there is a genetic cause. Twin studies suggest that many aspects of eating are indeed somewhat heritable. Body weight — measured as body mass index, or BMI — is highly heritable in both boys and girls. So is dietary restraint, or the mysterious urge to resist eating the thing you want to eat.
But studies that look at likes and dislikes are much less conclusive. In one study of 214 same-sex twins, identical twins were more likely to enjoy the same protein foods, but when it came to fruit and vegetables, their likes were only marginally more similar than with the pairs of non-identical twins. Overall, the evidence for tastes being heritable is very modest, accounting for only around 20 percent — at most — of the variation in foods eaten.
Genes are only part of the explanation for what we choose to eat. As one senior doctor working with obese children put it to me, you could be cursed with all the genes that make a person susceptible to heart disease and obesity and still grow up healthy, by establishing balanced food habits. “All of it is reversible,” he said. Parents and children resemble each other no more in the foods that they like than couples do, suggesting that nurture — the people you eat with — is more powerful than nature in determining our food habits.
Whatever our innate dispositions, our experience with food can override them. Maybe you share your parents’ hatred of celery because you have seen them recoil from it at the dinner table. Researchers found when they gave three groups of preschool children different varieties of tofu — one group had plain tofu, one ate it with sugar and one with salt — they quickly came to prefer whichever one they had been exposed to, regardless of their genes. It turns out that, so far from being born with genetically predetermined tastes, our responses to food are remarkably open to influence, and remain so throughout our lives.
Genes do make a difference — to the foods we like, the way we taste them and even how much we enjoy eating — but they turn out to be much less significant than the environment we learn to eat in. Apart from changing the infants’ food environment, there was another bigger trick to Davis’ experiment, one she did not mention, perhaps because it is so obvious. She radically changed the children’s social experience when eating, removing extraneous social influence. They ate without anyone caring what they ate, without any siblings fighting them for the last slice of pineapple, without any surrounding ideas about cuisine.
Davis was mistaken if she thought this was the way to discover the true nature of children’s appetites. Though the nutritional outcomes were excellent, it was a not-quite-human way to eat, and one that no child in a real situation will ever replicate.
We cannot arrive at the truth about appetite by removing all social influences. Appetite is a profoundly social impulse. To a large extent, our likes and dislikes are a response to the environment we eat in. From our first toothless tastes, we pick up cues about which foods are desirable, and which are disgusting, which sadly are so often the very ones the grown-ups most want us to eat.