Childhood Obesity Is In The Genes

Childhood obesity is down to nature not nurture, reports The Times and other news sources. Genes account for "more than three quarters of the difference between children's waistlines, with lifestyle factors such as diet and exercise playing a much smaller role", the newspaper adds. All the news stories focus on a message that it is wrong to blame parents for their child's weight as much of the variation is due to genetics.

The research behind these stories has looked at the "heritability" - an estimate of the extent to which characteristics (e.g. physical, behavioural, personality) are determined by genetic make up - of body mass index and waist circumference using a UK twin study which compared identical and non-identical twins. A limitation with these studies is that they cannot identify which genes are responsible.

The genetic component of risk for obesity is likely to be complex, including genes that affect appetite, personality, as well as how fat is deposited. However, a predisposition to obesity does not mean a child will definitely be overweight and parents should not abandon a healthy lifestyle, as there is good evidence of the benefits of weight reduction on health.

The researchers found that, overall, the twins' heights and weights were greater than the1990 averages, though BMI was similar. Waist circumferences were substantially higher than in populations in 1990, particularly in girls. They also found that identical twins were more likely than non-identical twins to have similar BMI and waist circumference measurements, suggesting a genetic component to these characteristics.

Using the modelling method, the researchers conclude that variation in BMI scores is 77 per cent heritable, while variation in waist circumference is 76 per cent heritable. They also found that the "shared-environment" had little effect on BMI and waist circumference (10 per cent each).

The researchers say that their modelling shows a substantial genetic influence on BMI scores and waist circumference and that their study is the first to have quantified the heritability of waist circumference. They have found that waist circumference is as heritable as BMI (though 40 per cent of this was due to different genetic factors). Their findings, say the researchers, mean that "blaming" parents for their child's obesity is wrong.