Written by Andrea Smith, Alison Fildes and Clare Llewellyn

In early childhood, children are gradually introduced to an increasingly varied diet. While some children happily accept new foods and enjoy eating lots of different kinds of foods, many are hesitant. Food avoidant behaviour can be broadly classified into two traits: ‘Food Fussiness’ and ‘Food Neophobia’. Food Fussiness is the tendency to be highly selective about the textures, taste and smell of foods you are willing to eat and is often seen as a consequence of inadequate parenting. However, Food Neophobia – the refusal to try new foods – is often seen as a normal development stage experienced by most young children regardless of the way their parents feed them. Fussy and neophobic eating behaviours typically emerge in toddlerhood and commonly peak between two and six years of age; but for some children these traits persist into later childhood.

Food avoidant behaviour can be both frustrating and worrying for parents; children who eat only a restricted range of foods might miss out on key dietary nutrients essential for healthy development. In particular, fussy eaters tend to reject nutrient-dense foods such as vegetables. Early childhood is also an important period during which food preferences develop; learning to like a range of healthy foods requires the child to try a wide variety of different foods. Researchers have therefore been interested in finding out what shapes food avoidant behaviour in early life. Some research has suggested that children who are breastfed for longer and whose parents use less persuasive feeding practices (e.g. rewarding with food) are less likely to display fussy eating behaviours; suggesting that there are important environmental shapers of this behaviour. On the other hand, Food Neophobia is associated with temperamental traits such as shyness or inhibition; these characteristics have an established genetic influence, indicating that neophobia might also have a strong genetic basis.

In a new study published in the Journal of Child Psychology and Psychiatry we used data from the Gemini twin cohort to investigate the extent to which genes and environmental factors influence children’s food fussiness and food neophobia. Gemini is a large study of 2400 pairs of twins that was set up in 2007 to explore early life growth and behaviour. Twin studies are useful for investigating the relative importance of genetic- and environmental factors on individual differences in traits such as food avoidant behaviours. The current study was based on data from 1,932 families collected when the twins where 16 months old.

We found that both food fussiness and food neophobia have a strong genetic basis, with 46% and 58% of the variation in each trait explained by genetic influences respectively. The shared home environment (which includes factors such as parental feeding practices) was a more important influence on Food Fussiness than Food Neophobia; but overall, these environmental factors were less important than a child’s genetic predisposition towards these behaviours.

The finding that there is substantial genetic influence on fussy eating behaviour in early childhood might be quite a relief for some parents who can often feel judged or guilty about their children’s fussy eating. Understanding that these traits are largely innate might help to deflect this blame.

However, our genes are not our destiny. Establishing the importance of genetic influences on fussy eating behaviours in early childhood does not imply that these behaviours cannot be changed. An effective intervention to overcome food rejection is through repeated exposure to the problem food; the more a child tries a food, the more familiar it becomes and the more they learn to like it. In our group we have developed a tasting game called ‘Tiny Tastes’ to help families introduce foods to reluctant and fussy eaters. This is an avenue through which parents might be able to positively change fussy or neophobic eating behaviours.

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Food fussiness and food neophobia share a common etiology in early childhood

Andrea D. Smith, Moritz Herle, Alison Fildes, Lucy Cooke, Silje Steinsbekk, and Clare H. Llewellyn

Article link: http://onlinelibrary.wiley.com/doi/10.1111/jcpp.12647/epdf

Written by Moritz Herle, Alison Fildes and Clare Llewellyn

Over the past century twin studies have been used to explore how nature and nurture influence individual differences in human characteristics (such as personality, intelligence or height). Identical twins share the same genes, while non-identical twins share about half of the same genes; but both types of twins grow up in the same family environment. This means that researchers can compare similarities between identical twins, and similarities between non-identical twins, to get an idea about how much differences between people in characteristics such as height are caused by nature (genes), and nurture (the environment).

The Health Behaviour Research Centre set up the Gemini twin cohort in 2007.  Gemini is a landmark study of early life growth and behaviour which has been following 2400 British families with twins born in 2007.  Gemini was established to help understand how genes (nature) and the environment (nurture) influence the development of eating behaviours, food preferences and growth in early childhood. Previous studies conducted by the Gemini team have suggested that individual differences in eating behaviours during childhood are strongly influenced by genes.

Like much research into early child development, these studies have had to rely on parents’ ratings of their children’s eating behaviour. This is because large sample sizes make it difficult to measure behaviours in a laboratory and because young children are unable to report accurately on their own characteristics. Parents of Gemini twins provided information about their children’s behaviour using a widely-used questionnaire called the Child Eating Behaviour Questionnaire (CEBQ).  However, a criticism of twin studies is that parents might be biased by their beliefs about their twins’ zygosity (whether they are identical or non-identical) when rating each of their eating behaviours. For example, parents of identical twins might rate them more similarly simply because they think of them as ‘two peas in a pod’, while parents of non-identical twins might exaggerate the differences between them. Because twin studies are based on the comparison of similarity between identical and non-identical twin pairs, reliable and unbiased parental ratings are crucial.

We recently published a new study that set out to test if parents are biased by their twins’ zygosity when they rate their eating behaviours. Using the Gemini sample we compared eating behaviour ratings from parents who held a false belief about their twins’ zygosity (i.e. they believed them to be non-identical, when they were in fact identical) to those from parents who held an accurate belief. The only way to conclusively know whether a twin pair is identical is to conduct a genetic test, which compares the DNA of the two siblings. However these genetic tests are not routinely carried out and parents can sometimes be misinformed about their twins’ zygosity. A more thorough account of why these misunderstandings occur has been discussed in a previous study.

We established whether the Gemini twins were identical or non-identical using a combination of DNA testing and a questionnaire that accurately measures twin similarity. We also asked parents about whether they thought their twins’ were identical or not. Using this information we were able to identify parents who held a false belief about their twins’ zygosity, and those who were right. We found that approximately one third of parents of identical twins falsely believed them to be non-identical when they were about eight months old.

In order to test if parents’ ratings of their twins’ behaviours are biased by their beliefs about their zygosity, we compared the ratings of parents with false and accurate beliefs about their twins’ zygosity, on a range of eating behaviours during infancy and toddlerhood. If parent ratings were biased then we would expect identical twins whose parents believed them to be non-identical to be rated as less similar than identical twin pairs correctly identified by their parents as identical.

Interestingly, parents’ reports of their identical twins’ eating behaviours were the same, regardless of whether they had false or accurate beliefs about their twins’ zygosity. In other words, parents rated identical twins as more similarly than non-identical twins on all eating behaviours (in both infancy and toddlerhood), regardless of whether they believed them to be identical or non-identical. This indicates that parents of twins can be relied upon to provide unbiased reports of their young children’s eating behaviour, and that findings from twin studies can be trusted.

Article link:

Herle, M., Fildes, A., van Jaarsveld, C., Rijsdijk, F. & Llewellyn, C. H. (2016). Parental Reports of Infant and Child Eating Behaviors are not Affected by Their Beliefs About Their Twins’ Zygosity. Behavior Genetics. doi: 10.1007/s10519-016-9798-y

All animals need it, we go crazy without it, yet, we don’t understand it well – no, I am not talking about love here, but a much less considered, although just as profound, need: The need for sleep.

Sleep is currently a ‘hot topic’ in science, because it appears that it is vital for all other major systems in our brains and bodies to function well – from how we feel , how well our muscles function, how well we concentrate, to the food choices we make.  Moreover, there is growing evidence that shorter sleep is linked with a large number of diseases, such as obesity, heart disease, cancer, lowered function of the immune system and mental health problems.

Although, as a nation overall, we sleep less than ever before, individuals vary substantially in the need for sleep –your partner may be chirpy after 7 hours, whereas you may need more to feel human.  Interestingly, variation occurs even in the same families and among siblings; this raises the question of whether genes play a role in determining how much sleep a person needs, because families usually share a very similar environment.  However, very few large studies have looked at what influences sleep early in life, when sleep is assumed to be mainly governed by the infant’s ‘body clock’.  Twins are especially useful to tease the question of ‘nature’ and ‘nurture’ apart, because twins are either 100% genetically identical; or they share half of their genes, just as ‘normal’ siblings.  Both, however, usually share the same environment, because they are born at the same time.  Our researchers used data from the GEMINI birth cohort, which includes twins from about 2000 families, to take a closer look at the genetic and environmental influences of sleep in young children.

Perhaps surprisingly, the results showed that sleep duration and daytime nap duration were mainly influenced by the environment. Likewise, sleep disturbance was due to environmental influences, although the genetic effect was slightly bigger than for sleep duration.  This was true for both girls and boys.  Although it could be argued that the carer’s schedule determines infants’ sleeping time, it would be expected that they would adjust bed-and nap times according to the infants’ needs.  Unfortunately there was no data available on when the infants actually went to sleep once they were put to bed, so we cannot say for sure how long they actually slept.

This study shows that, as so often, nature and nurture both act together to influence how we behave; in this instance, how much and how well we sleep.  Nonetheless, the study is important, because it shows that being a ‘morning vs. evening’ type person is indeed influenced to an extent by genes and this is apparent already very early in life. However, what is more important, the study clearly shows that the home environment is a crucial factor for providing children with a good night’s sleep. So, it might be wise to practice good ‘sleep hygiene’ (and that is not only true for kids): Remove the TV from the bedroom, have a consistent bedtime routine, put your kids to bed before 9pm if they are under 10 years old, let them fall asleep without anyone present, and limit (soft) drinks containing caffeine.  That will, hopefully, help your kids, and ultimately you, too, to get the well-deserved snooze.

Source

http://pediatrics.aappublications.org/content/early/2012/05/09/peds.2011-1571.abstract

As mentioned in one of our previous blog posts, talking about genes in the context of obesity is often not well received.  Those discounting their role in the development of obesity often argue that, because genes have not substantially changed over the past 200 000 years, whereas obesity levels have only been soaring over the past 20 odd years (where it became possible to mass-produce cheap, tasty food in combination with a decreased need for physical activity), obesity must be due to changes in the environment, and not genetics.

However, using this argument against the heritability of obesity is somewhat flawed, because it ignores that a condition can be dormant over a period of time until the right circumstances bring it to life.  The gardeners among you will know that many plants will adjust their growth according to their surroundings – a plant in a small pot will remain small, whereas a larger pot will allow it to grow.   This, however, does not mean that the plant loses its ability to grow larger in a smaller pot; it merely remains small because its surroundings restrict its growth.  Similarly, genes predisposing to obesity may be present in an environment where little food is available, but without the right ‘medium’ (i.e. food), this is of little consequence.  In the current environment, however, where eating opportunities are plentiful, obesity genes can express their full force.

If obesity was resulting purely from environmental change, all individuals exposed to this change would become overweight.  Yet, this is not the case. In fact, the proportion of lean people has not substantially changed, but large people are becoming even larger.  This suggests that people respond to the food environment differently.  However, undoubtedly, to gain more weight than is healthy, food must not only be available in sufficient quantities, but one must ingest more of it than necessary.  Therefore, researchers started to look at differences in eating behaviours, such as how much we are drawn to food and how quickly we feel full, to see what is going on.

Twins can help to untangle the influence of genes and environment on obesity, because identical twins are 100% genetically identical, whereas non-identical twins only share approximately half of their genes (like normal siblings); both, however, grow up in a very similar environment.  This means that researchers can compare identical twins’ resemblance for weight with that of non-identical twins; if genetically identical twins are more similar in a trait than non-identical twins, it is evidence for genes being responsible for the trait.

Using twins, researchers from our department wanted to see whether genes that influence weight also influence appetite.  If the same genes that influence weight also influence appetite, it suggests that genes influence weight through their effects on appetite – i.e. individuals who inherit more avid appetites might be more susceptible to overeating in the modern food environment, and consequently  more likely to gain excessive weight.  They looked at this in infants, because infants are exclusively milk-fed, which ruled out that other factors such as preference for certain foods would influence the results.   The researchers used questionnaires to ask parents about how fast their twins fed, how easily they got full and how big their appetite was, and related the answers to the babies’ weight.   Because they used a sample of identical and non-identical twins the researchers were able to explore the extent to which appetite is heritable, and the extent to which appetite and weight are caused by the same genes.

They found that identical twins were not only very similar in weight, but shared many more similarities in appetite than non-identical twins, suggesting a strong genetic basis to both appetite and weight.  In addition, the results  showed that a substantial proportion of the genes that are responsible for weight are also responsible for appetite, in line with the idea that genes influence weight through appetite.  These findings lend evidence to the idea that some of us are more likely to overeat in the current environment because of a larger appetite, which is ultimately driven by genes.

These discoveries will hopefully contribute to reducing the stigma that surrounds unhealthy weight gain; because it clearly shows that those struggling with weight are in a sense ‘battling against their biology’.  This of course, does not mean that there is nothing that can be done about it; however, acknowledging these differences as real and designing strategies to ‘outsmart’ one’s genes is crucial if the battle is to be fought successfully.

Article reference: http://www.ajcn.org/content/95/3/633.long