Sussex study finds that parents contribute to their child’s BMI by 35- 45% and this increases for children of obese parents

Researchers at the University of Sussex have disovered something many of us could have guessed at – people look like their parents, in this case with regard to body size. They’ve also taught us something new; the amount that parents contribute to their child’s BMI is consistent across countrie, even when they have varying levels of economic development.

The pair conducting the study, Peter Dolton from the University of Sussex and Mimi Xiao from the London School of Economics, trawled through data containing the heights and weights of 100,000 children and their parents. The data collected was from six different countries: the UK, USA, China, Indonesia, Spain and Mexico.

A child’s BMI is, on average, 20% due to the mother and 20% due to the father

They found that the intergenerational transmission of BMI is approximately 0.2 per parent. In more relatable terms this means that a child’s BMI is, on average, 20% due to the mother and 20% due to the father, meaning that the parents have a combined effect of 40% on their child’s BMI. The contribution of 20% per parent remained fairly consistent across all six countries, despite the countries being of developing economic status and developed economic status.

Parents have a considerable influence on their child’s body size, not only via genetics but also through the family environment which includes decisions on what to eat, how much time to spend exercising and how to spend family time. Although this study doesn’t untangle the individual contributions of genetics and family environment, it is clear that these two factors are of considerable value in determining a child’s weight.

When comparing BMI data from different countries there is an issue of ethnicity influencing BMI as well as parental influence. The researchers admit to being stumped by this problem and state in the paper, published in Economics and Human Biology, that ‘this problem is not solved’. They do suggest, however, that many of the countries in the study have considerable ethnic diversity in their populations which reduces the contribution of ethnicity to the data set.

When looking at the BMI data sets individually, there is a trend for developed countries to have higher BMIs. Developing countries are shifted left on the graph indicating the population has lower BMI, with Indonesia being the leanest population in the study. Developed countries are shifted right indicating a higher population BMI – the UK being the fattest population.

Parents have a considerable influence on their child’s body size, not only via genetics but also through the family environment

The data becomes particularly interesting when the extremes of the population are taken into account. At the top end of the BMI scale it seems that parents have a greater influence on their child’s BMI, with the total parental contribution being about 50%. This means that the shared environmental and genetic factors between parents and child tend to be larger for more obese children.

Looking at the opposite end of the spectrum, the thinnest children, seem to have a lower contribution from their parents. The lowest is a 25% total parent contribution. This may represent the lowest feasible value of parental influence on a child’s body weight and so could represent the genetic contribution to BMI.

Achieving long-term weight reduction in obese children is incredibly challenging and is a problem that has long plagued clinicians. This study highlights the importance of the family in childhood obesity and may explain why weight loss interventions tend to fail. In order for future programs to be more successful they should focus on the child’s family environment rather than the child’s own actions.

IMAGE: flickr

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Kate Dearling

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