Child obesity could be 35 per cent to 40 per cent inherited from parents — irrespective of the child's country of residence — according to a new international study of 100,000 children in six different countries worldwide.
Research carried out by the University of Sussex in the UK —studying children in the U.K., the USA, China, Indonesia, Spain and Mexico — found that the more obese the child, the more their BMI was dependent on genetic inheritance from their parents.
Obesity is defined as a body mass index of over 35. A BMI of between 18.5 and 25 is considered healthy. BMI is calculated by dividing a person's weight in kilograms by their height squared in metres.
For the 100,000 children studied, around 35-40 per cent of their BMI (defining how fat or thin they are) was found to be inherited from their parents, with 20 per cent from the mother and 20 per cent from the father. For the most obese children, the proportion of parental effect rose to 55-60 per cent.
The researchers discovered a lower parental effect on BMI in the thinnest children, with 10 per cent inherited from the mother and 10 per cent from the father. This was closer to 30 per cent from each parent for the fattest children. What's more, the pattern proved consistent across the countries studied, irrespective of their economic development, industrialization or type of economy.
In China, less than 1 per cent of children and adolescents were obese in 1985. However, obesity levels reached 17 per cent for boys and 9 per cent for girls in 2014, echoing obesity levels in American children aged two to 18 years old (17.4 per cent).
Beyond healthy eating and lifestyle factors — which are essential in the fight against obesity — the study gives important insight into how obesity can be transmitted from generation to generation.
"We found that the process of intergenerational transmission is the same across all the different countries," explains lead author Professor Peter Dolton of the University of Sussex.
Global obesity levels are rising rapidly, with around 650 million adults, or approximately 13 per cent of the world's adult population, currently considered obese. This could rise to 20 per cent by 2025 if the current rate of progression is maintained, according to a study published in The Lancet in April 2016. According to figures published in October 2016 by Eurostat, the statistical office of the European Union, 15.9 per cent of Europeans are obese.
In the USA, approximately one in five pregnant women is thought to be overweight or obese.