Childhood obesity can begin in the womb and could be triggered by the mother's high blood sugar levels, scientists warn.
They have found that babies born to women with a common form of temporary diabetes that occurs in pregnancy gain weight early on in life.
Researchers from Imperial College London found that at just ten weeks old, these newborns had 16 per cent more body fat than others. They studied mothers with gestational diabetes, a condition which affects 120,000 expectant mothers in England and Wales each year.
It only affects women during pregnancy and occurs when they have too much sugar in the blood, which can lead to complications including miscarriage and stillbirth.
This blood is passed on to the unborn baby via the placenta and scientists think it may trigger crucial changes in its metabolism, which lead to obesity.
The study published in the journal Diabetes Care looked at 42 babies to mothers with gestational diabetes with 44 born to healthy women.
Dr Karen Logan, lead author of the study, said: "Gestational diabetes is becoming more and more common, and babies born to these mothers are at increased risk of developing diabetes when they grow up."
Researchers said newborns were also overweight even if they were breastfed - which normally means they are slimmer than those reared on formula milk.