Biology in the News Explained

You are responsible for how your children eat

Once again, the mass media can’t tell real science from a junior high fair project. Genetics is the new path to a guilt-free style of life and child-rearing; it has been mass-marketed to people who want to evade all responsibility for persistent unpleasant conditions ranging from obesity to bad behavior, not to mention sexism. This is especially true in the field of child-rearing, where there has been a backlash against the offensive “blame the mother” explanations for problem children espoused decades ago. As usual, though, the backlash has swung too far in the other direction, making parents completely blameless. Bad papers supporting this faddish view continue to be published simply because they generate positive press.

The latest condition to be given a free pass is picky eating by children, in a study (Cooke, L.J., C.M.A. Haworth, and J. Wardle, 2007. Genetic and environmental influences on children’s food neophobia. American Journal of Clinical Nutrition 86:428-433) using the differences between the eating behavior in identical twin pairs and in fraternal twin pairs. The idea is that twins in each pair are both presumably reared in the same environment, and so if there is a bigger difference in fear of new foods (=”neophobia”) between fraternal twins than there is between identical twins, this behavior must be genetic, thus, it’s not the parent’s fault that a child is picky.

The press release demonstrates the first problem with this paper:

“People have really dismissed this as an idea because they have been looking at the social associations between parents and their children,” Dr. Cooke said. “I came from a position of not wanting to blame parents.”

This of course explains the absurd conclusions of this paper – apparently, the first author had decided what the results should be before the study was conducted.

As usual with human health papers, the authors commit the fallacy of believing that a bigger sample size is better. They admit up front that a previous paper failed to find that genetics played a role in picky eating, but discount it by asserting that its sample size of 91 was too small. This of course is a circular argument; the authors are defining 91 as too small a sample size because no effect was found.

The data from the study are from parents completing questionnaires on the pickiness of each of their twin children, answering four questions on a scale of 1 to 4. They determined that fraternal twins were more different in their food choice than identical twins, based on a difference in survey score of 0.03 on that scale. Such a minute difference could of course only be detected by an enormous sample size, which they had – 5390 twin pairs. When a huge sample size is needed to detect a difference, it is unlikely that difference is biologically meaningful. This result is thus consistent with that of the previous paper which was unable to detect a difference with its sample of 91 twin pairs. It is especially egregious that the authors try to pass off their result as meaningful, when two other analyses associated with the paper that did not contribute to the support of their theory, but were statistically significant, were dismissed because these results were “statistically significant only because of the large sample size.”

The other fundamental problem with the study is the fact of its reliance on evaluations of pickiness by parents. Think about it for a moment: parents with identical twins often dress them the same, give them the same toys, and refer to them as a unit, while parents with fraternal twins are much less likely to do so. The tiny difference that was found could be merely due to a bias by parents of identical twins, in their unconscious assumption that the children are naturally similar. This is separate from the possibility that there would probably be a greater correlation between identical twins than fraternal twins in personality traits that manifest themselves as food pickiness, apart from any genetic determination of pickiness per se. And, while the questions addressed the children’s behavior toward new food, there was no data on how often the children actually encountered new food.

Obviously there are clear genetic differences in how individuals taste food. This is known from research on taste receptors. Given this, it is actually surprising that a study that set out to show genetic differences in food exploration found such a slight effect. Nevertheless, the publicity surrounding this non-result will lead people to believe that they cannot control their children’s stated food preferences, and thus must give in to them. This is an unfortunate implication, because it could lead to an even larger number of adults in the next generation subsisting on McNuggets from the drive-thru as they drain the health system with their obesity-related conditions.

You do have a choice about whether or not your children will eat anything besides tater tots. Give them the food you have cooked for the family, and if they don’t want to eat it, fine. They really will not starve to death between dinner and breakfast. (For a lot more advice in this vein, read Ellyn Satter.)

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