Its not just human toddlers that are fussy eaters
Every parent knows the clenched-teeth frustration of a child that refuses to eat their
dinner. But children may behave this way for a good reason
Toddlers can be the harshest of food critics. No matter how much care and attention a parent has put into cooking a meal, a two-year-old may still turn up their nose and refuse to eat. Many are particularly likely to reject new and unfamiliar foods, with vegetables often top of the list.
Frustrating though this is for parents, they can draw some comfort from the fact that toddlers are not the only fussy eaters in the world. Many young animals are cautious about trying new foods.
It seems bizarre at first. Food is often short, so why would a toddler or young animal refuse to eat when it is available? A full explanation is still some way away, but biologists have developed several ideas that can help to explain why.
Lucy Cooke, a psychologist at University College London and Great Ormond Street Hospital, has been studying childrens eating behaviours for over 15 years.
A child who is wary of something new might have a broad repertoire of familiar foods they are perfectly happy to eat
She draws a distinction between two forms of fussy eating in young children. On the one hand there are picky eaters children who have a limited range of accepted foods. On the other hand, there are children who are neophobic avoiding any foods that are new or unfamiliar.
Cooke says there is endless debate over whether or not food neophobia and picky eating (or food fussiness) are connected. Logic suggests they might not be.
Food neophobia is a general problem that is seen in essentially all the children she works with and is, in fact, a trait shared to some degree by most people whereas a more general food fussiness seems to be a less common additional problem seen in some children.
If you have a very picky child, with a very restrictive diet, they are almost by definition going to be neophobic, she says. But flip that around, and a child who is wary of something new might have a broad repertoire of familiar foods they are perfectly happy to eat.
Cooke is a member of a research team that is exploring the subject by studying a group of twins born in England and Wales in 2007.
The parents of the children in the study called Gemini regularly complete questionnaires about their childrens eating habits. This gives the researchers an opportunity to explore whether traits like food neophobia and food fussiness are down to nature or nurture: in other words, whether they are controlled by genes or by a childs home environment.
Certain things are genetically determined and dont differ between people. We are almost all born with two arms and two legs, for instance, says Clare Llewellyn at University College London, another Gemini researcher. But other things are variable: differences in height, weight, eye colour. Twin studies can tell us whether those differences are shaped by different environmental factors, or whether genetic differences between people play a role.
Some children may be born with an innate fussiness about food
The studies take advantage of the fact that identical twins share 100% of their DNA, whereas non-identical twins share just 50%. If a trait like food neophobia is more likely to be seen in two children who are identical twins than in two children who are non-identical twins, it hints that the trait is controlled to some extent by genes.
One paper the Gemini research team published in October 2016 made the headlines. Many of the reports missed the main message of the paper, which was that food fussiness and food neophobia are strongly correlated and might, after all, be caused by common factors.
But a broader message from the study did get through: the research had uncovered evidence that both forms of fussy eating are, to some degree, genetically determined. To put it another way, some children may be born with an innate fussiness about food, and parents are not necessarily to blame if their child becomes difficult at mealtimes.
The results were actually a little more complicated than that.
Genes do play a role in both food neophobia and food fussiness, but the study suggested genetics are not an overwhelming factor in determining a childs attitude to eating. Food fussiness heritability was 46%, says Llewellyn. Heritability of neophobia was a bit higher, about 58%.
This means a child who inherits fussy genes will not necessarily become a fussy toddler. Their upbringing and experiences can have a roughly equal impact on their eating habits.
Our ancestors gained a substantial proportion of their diet from plants
Dig deeper into the literature and things become even more complex.
The Gemini twins were 16 months old when their eating habits were explored for the 2016 study. But earlier research projects have looked at fussy eating in groups of slightly older twins, and they tell a different story.
For instance, in 2013 a research team studied food neophobia the more common form of picky eating in four- to seven-year-olds. They found the heritability at this age was almost 72%, which is far higher than in the 16-month-old Gemini twins.
This suggests the genes that influence a childs tendency to food neophobia gradually exert a greater influence as children grow older. There is quite a profound increase in the genetic effect, says Llewellyn.
Why might that be? One longstanding idea offers an explanation.
Humans are, traditionally, a foraging species. Our ancestors gained a substantial proportion of their diet from plants. Unfortunately, plants particularly those in the tropics, where our species evolved often contain toxins.
It would be evolutionarily advantageous for those children to suddenly become far more wary of trying new foods
This left our ancestors facing a problem. They had to sample as many different plants as possible, to build a broad diet and increase their chances of survival. But they had to balance that willingness to try new plant foods with wariness, because those leaves, stems and roots might turn out to be highly toxic. This is sometimes called the omnivores dilemma.
A child should not experience the omnivores dilemma in their first year or so. At this stage, parents are carefully selecting all of the food a child eats, so in theory, the child should be willing to eat anything it is given.
But children gain more independence from about 24 months.
They can toddle around and explore their environment and the food it contains. It would be evolutionarily advantageous for those children to suddenly become far more wary of trying new foods, just in case the food was dangerously toxic. Consequently, it would make sense for the genes that influence food neophobia to become more active at this point in childhood.
Evolution should have favoured children who gobble down things like peas and broccoli with relish
Arguably, this attitudinal shift towards food should be really rather dramatic.
Adults have mature biological systems for dealing with toxins in their food. Eating the wrong plant might lead to an unpleasant stomach upset, but probably will not threaten their lives. But in general, youngsters lack those systems, so eating the wrong thing at this age could result in death. It would make sense for the omnivores dilemma to be at its most acute in toddlers and almost non-existent in infants.
These ideas offer explanations for some of the problems parents may have to deal with at dinnertime. Most obviously, they could help explain why children often refuse to eat their greens.
It seems baffling why so many children have a problem with green vegetables. These foods are very nutritious, so evolution should have favoured children who gobble down things like peas and broccoli with relish.
Food neophobia seems to kick in when children are between their second and third birthdays
But perhaps over the long expanse of human evolution it has been the omnivores dilemma not the nutritional value of vegetables that has played the leading role in deciding which children survive to adulthood and pass on their genes.
In line with this, most of the vegetables on the dinner table today have been selectively bred to be far more nutritious, and far less toxic, than they would have been in the past. A childs reluctance to eat their greens might be a hangover from a time when those foods were less nutritionally beneficial, and more likely to be dangerous.
These ideas provide a neat and satisfying explanation for picky eating among toddlers. But are they actually supported by evidence?
Elizabeth Cashdan, an anthropologist at the University of Utah in Salt Lake City, explored the subject in a study published in 1998. At the time, she found hardly any formal scientific studies on whether infants really are willing to eat anything, before turning into recalcitrant toddlers. So she began collecting data herself.
The single greatest cause of poisonings among six- to 18-month-old children was eating houseplants
Her findings were, indeed, broadly in line with the ideas of the omnivores dilemma. Food neophobia seems to kick in when children are between their second and third birthdays, and to get worse by the time children hit their fourth birthday. This is in keeping with the recent twin studies, which suggest genes begin to exert a greater influence on a childs eating habits sometime between the ages of 16 months and four years.
Cashdan also found that the threat plants pose to young children, even in todays developed societies, should not be underestimated.
She talked to the Utah Poison Control Center, a medical facility that offers advice to Utah residents about exposure to toxic substances. All sorts of potentially toxic cleaning products and medicines are kept in the typical home.
- BBC
