The study in journal Diabetes found a blood test could enable families to change the lifestyles of their children before they start piling on the pounds.
A simple blood test could predict whether children as young as five are at risk of becoming obese in later life.
The test, which looks at a fat storage gene, will enable parents to change the lifestyles of children before the pounds pile on.
Blood samples from 40 children, aged five to 14, were used to predict how likely they were to store body fat in early life independent of gender, activity and puberty.
Dr Graham Burdge, of Southampton University, said the results could help catch those youngsters at risk of Type 2 diabetes in childhood and heart disease in adulthood.
He said: The study shows being overweight in childhood is not just due to lifestyle.”