London, April 27 Whether a 10-year-old child is slim or overweight is explained mostly by genetic factors, scientists suggest urging parents to be more vigilant and aware of what their children are eating.
A recent study, involving more than 2,500 pairs of twins, suggests that genes account for 82 per cent of the variation in body mass index in 10-year-olds. The influence of genes on weight appeared to increase substantially throughout childhood, which scientists put down to older children having more freedom to act on their urge to eat.
Clare Llewellyn, an epidemiologist at University College London, said: "When you're four years old, your parents decide how much to feed you. By the age of ten, you might be the child who always asks for seconds or goes for a snack from the fridge."
Previously, several genes linked to obesity had been shown to influence appetite and self-control. However, the scientists said that the finding did not suggest that certain children were destined to be obese. Parents needed to be stricter about food, they said.
"Parents should be more vigilant and aware of what their children are eating," said Dr Llewellyn. "Even at primary school there's considerable scope for children to buy food at school or on the way there."
The study, published in the journal Obesity, compares the body mass index (BMI) of 2,556 pairs of twins in Britain, at the ages of four and 10.
Since twin analyses do not involve direct measurement of genes, the researchers used genomic data in the same sample to compare with the twin findings.
Update: 27 April, 2014