Babies given formula milk instead of being breastfed are 25 per cent more likely to become obese, major international research has found.
Almost one in six bottle-fed babies are obese at the start of primary school, according to the study of more than 100,000 children aged six to nine.
Experts believe formula may cause babies to gain more weight and grow faster because it is developed from cows’ milk, which has higher levels of protein and may trigger the growth of fat cells.
Despite this, only around 1 per cent of mothers in Britain breastfeed their child for at least six months without using a bottle.
The study, promoted by the World Health Organisation, looked at breastfeeding rates for up to 22 countries, finding that even nursing babies for some of the time may protect them from obesity.
Breastfeeding is known to reduce the risk of babies being overweight, which may be due to hormones, nutrients and healthy bacteria in breast milk.
It is also believed to ‘programme’ babies to burn fat more efficiently in later life instead of storing it.
Breast milk may also give them a taste for healthy food as it can contain traces of fruit and vegetables from their mother’s diet.
But formula milk is thought to increase their insulin levels, which may cause them to grow extra, bigger fat cells, and contains sugars that can lead to obesity.
Those never given breast milk have 25 per cent higher odds of obesity than those whose mothers exclusively breastfed them for at least six months. Children who were breastfed for at least six months and given bottles were 22 per cent less likely to be obese than those never breastfed.
Infants breastfed for less than six months were 12 per cent less likely to be obese than those never breastfed. Children who nursed exclusively for this period were 5 per cent less likely to be obese.
Dr Joao Breda, senior author of the study, said: ‘We need to see more measures to encourage breastfeeding, like properly paid maternity leave.
‘We need less inappropriate marketing of formula milk, which may lead some mothers to believe it is as good for babies as breast milk, and it would be an excellent idea if countries like the UK with low levels of exclusive breastfeeding tried to reach the European average, so that more than 20 per cent of women managed this.’
The health watchdog NICE recommends that babies should be breastfed exclusively for their first six months. Almost one in ten British children are obese before they start school.
The breastfeeding study, the largest of its kind, was presented at the European Congress on Obesity in Glasgow.
Dr Breda, of the World Health Organisation, said: ‘Breastfeeding has a really strong protective effect. The benefit is outstanding.’
Sue Ashmore, of Unicef UK’s Baby Friendly Initiative, said: ‘Breast milk is specifically designed for human babies.
‘Not only does it act as baby’s first vaccine, protecting against infections, but it also affects long-term health, including acting as the first defence against the epidemic of obesity.’