The science of picky eaters

Why kids reject foods that you like

© 2009 -2013 Gwen Dewar, Ph.D., all rights reserved

The sensory world of picky eaters

Does your child want to live on a diet of sugar and starch? Or refuse to try anything new?

Picky eaters can be frustrating. But their quirks and preferences aren’t entirely arbitrary.

Simply stated, your child’s taste perceptions may differ from yours. There are several reasons.

Compared to young children, adults are more tolerant of bitter and sour flavors.

Perhaps this reflects a lifetime of learning. Experiments show that kids increase their liking for bitter or sour foods if they first encounter them in combination with something sweet (Capaldi and Privitera 2008). As I note elsewhere, you can take advantage of this phenomenon to broaden your child's diet.

But the point here is that adults have already had many opportunities to develop such acquired tastes. Picky children may be lacking crucial experiences.

Adults might be less sensitive, too.

Bitterness is a signal of potential toxicity, and kids—with their smaller bodies and less-developed capacities for detoxification—are more vulnerable to the effects of toxins.

You might assume that the fruits, vegetables, and spices we eat are safe, but many common plant foods contain natural toxins. Indeed, biologists believe that many of the toxins we find in plant food evolved precisely to deter animals from eating them.

Some toxins make you ill. Others bind to the nutrients in your food, making them indigestible. Either way, toxins can make foods less healthful.

This doesn’t mean that all bitter foods are bad for us. Many bitter herbs and “hot” spices have medicinal properties. But it explains why animals--especially those animals that lack specialized systems for detoxifying poisons--might be better off if they avoid bitter foods. It wouldn’t surprise me if natural selection has equipped children with an extra-sensitive system for rejecting bitter tastes (Glenndinning 1994).

Young children may be “prewired” to select the most energy-rich foods available.

Ounce for ounce, kids need more food than we do. Not only do kids need more food to grow, they need more food because they are less energy efficient.

It’s because of their size. Smaller bodies tend to have more surface area relative to volume, so they lose more body heat. Smaller creatures also tend to have smaller, shorter digestive tracts, making it more difficult to digest food that is high in fiber and/or toxins.

So natural selection has put the squeeze on little guys: They need to focus on foods that deliver a lot of energy with little bulk. That’s the trend we see among primates. Little squirrel monkeys go after nature’s “fast food,” fruit and insects. Large gorillas can afford the extra processing time associated with pithy leaves and stems.

Does this imply that our kids are picky eaters by nature? I’m not sure. But as a behavioral ecologist, I think it’s reasonable to wonder if kids have evolved a special attraction for the sweetest and/or most energy-rich foods.

Some people have a genetically-based, heightened sensitivity to bitterness.

We’ve seen how youth and body size might make kids into picky eaters. But there are other factors, too. Recent research demonstrates that people--even people in the same family--possess different bitterness-detection genotypes.

In one study, Julie Mennella and colleagues presented kids (aged 5 to 10 years) with a series of bitter- and sweet-tasting drinks. The researchers found that the children’s preferences were related to their genotypes at the TAS2R38 locus, a region that controls an individual’s sensitivity to several similar, bitter-tasting compounds, like PTC (Mennella et al 2005).

The researchers found that kids who possessed at least one copy of the bitter-sensitive allele were more likely to detect bitterness at low concentrations. In addition, these kids reported preferences for sweeter drinks and cereals with higher sugar content. They were also less likely to name milk or water as a favorite beverage.

And here’s a particularly interesting bit for us parents:

Kids with the bitter-sensitive genotypes were rated as “more emotional” by their mothers if their mothers possessed only bitter-insensitive alleles.

So some perhaps some of the conflicts between picky eaters and their parents are caused by a genetic mismatch. Parents who can’t taste certain bitter compounds have more difficulty relating to the way that their kids react to bitter foods.

Other people may have a genetically-based predisposition to avoid new foods.

A recent twin study examined the possibility that food neophobia—the reluctance to eat new foods—is genetically determined. Researchers found that identical twins were more likely to share neophobic traits than were fraternal twins. Overall, about 2/3 of the variation between individuals was attributable to heredity (Knaapila et al 2007)

Other factors

Early taste experiences may influence picky eaters.

Research suggests that fetuses can taste the foods that their pregnant mothers eat. Food flavors also get transmitted through breast milk.

These early taste experiences may shape the taste preferences of young children, making kids more likely to enjoy the flavors they previously encountered in the amniotic fluid or breast milk.

Picky eaters are also influenced by social cues, parental feeding tactics, and the ways that new foods are presented.

For instance, one study of over 7800 British kids examined links between the introduction of "lumpy solids" or chewy foods during infancy and subsequent feeding behavior. Compared with babies introduced to lumpy solids between 6-9 months, babies introduced later had less varied diets and more feeding problems by the age of 7 years (Coulthard et al 2009).

Other studies suggest that making toddlers familiar with new foods -- by presenting them with images in picture books -- has a positive effect on food acceptance (Heath et al 2011). And there are many other practical tactics parents can use to get children to eat.

For more information, see these research-based tips on coping with picky eaters.

In addition, check out this discussion about the special dietary needs of young children and their implications for choosing a healthful diet for your family.



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References: The science of picky eaters

Capaldi ED and Privitera GJ. 2008. Decreasing dislike for sour and bitter in children and adults. Appetite. 50(1):139-45.

Coulthard H, Harris G, and Emmett P. 2009. Delayed introduction of lumpy foods to children during the complementary feeding period affects child's food acceptance and feeding at 7 years of age. Matern Child Nutr.5(1):75-85.

Fleagle J. 1999. Primate adaptation and evolution, 2nd edition. San Diego, CA: Academic Press.

Glendinning JI. 1994. Is the bitter rejection response always adaptive? Physiological Behavior 56: 1217-1227.

Heath P, Houston-Price C, and Kennedy OB. 2011. Increasing food familiarity without the tears. A role for visual exposure? Appetite 57(3):832-8.

Knaapila A, Tuorila H, Silventoinen K, Keskitalo K, et al. 2007. Food neophobia shows heritable variation in humans. Physiol Behav 91(5): 573-578.

Mennella, J.A., Nicklaus, S., Jagolino, A.L., and Yourshaw, L.M. 2008. Variety is the spice of life: Strategies for promoting fruit and vegetable acceptance in infants. Physiology & Behavior 94: 29-38.