The Flinders University study found that infants breastfed for six months or more were 36 per cent less likely to be overweight and 49 per cent less likely to be obese at 16, compared with those who were not breastfed.

The short-term benefits of breastfeeding in preventing certain illnesses are well known but Jane Scott, a professor of nutrition and dietetics at the Adelaide university, said the research added to evidence that the benefits of breastfeeding extended to later life.

''There's such a lot of studies that have found this association, but this was the first large, nationally representative study carried out in Australia,'' she said.

Of the 2066 children and adolescents aged between nine and 16 who were studied, 90 per cent were breastfed at birth.

While 45 per cent of them were still breastfed at six months, only 10 per cent of those were fed on breast milk exclusively.

''Even once we accounted for factors known to influence weight - including the mother's age, ethnicity and level of education, and the child's energy intake, exercise habits and sleep time - breastfeeding still appears to reduce the risk of becoming overweight,'' Professor Scott said.

A likely reason for that, she said, was because breastfeeding was infant-led while bottle-feeding was mother-led.

''What happens with breastfeeding is if the infant isn't hungry, they won't eat. With formula, mothers can get preoccupied with making their child finish the bottle. Initially the child will stop when satisfied, but Mum keeps putting the bottle back in the baby's mouth.

''They are teaching their children to override their innate ability to stop when full.''

At 10 months old, Zoya is still being breastfed by her mother, Gunjan Chamania, who said she chose to breastfeed because of the health benefits.

''It's hard at the beginning; it's a learning experience both for the baby and the mum, so I can't say it's very easy,'' Mrs Chamania, of Macquarie Park, said.

''But I will definitely breastfeed for as long as Zoya wants, because it is obviously good for her.''

However, Professor Scott said breastfeeding for a period of at least six months was not a guarantee against weight gain.

''It reduces the risk, but doesn't guarantee prevention,'' she said.

''There are other lifestyle practices that children still need, like adequate physical activity, eight hours or more of sleep, less than two hours of screen time per day and a diet low in sugar and fat, to help prevent them from becoming overweight.''

with Elizabeth Pratt