Milk protein clue to big babies
How babies are fed is the subject of much debate
Breast milk has less protein than formula, which could be why bottle-fed babies grow faster, a study suggests.
There has been concern that formula-fed babies, who tend to be bigger, are "programmed" to store fat and so have a higher risk of childhood obesity.
The international study of 1,000 babies, published in the American Journal of Clinical Nutrition, suggests protein levels in formula should fall.
But UK manufacturers said action had already been taken to cut levels.
The study was carried out in Belgium, Italy, Germany, Poland and Spain on babies born between 2002 and 2004.
Parents were recruited to take part in the first few weeks of their babies' lives.
A third were given a low protein content formula milk (around 2g per 100kcal), a third had a formula with a higher level of protein (3-4g per 10kcal), while the rest were breast-fed during their first year.
Limiting the protein content of infant and follow-on formula can normalise early growth and might contribute greatly to reducing the long-term risk of childhood overweight and obesity
Professor Berthold Koletzko, Study author
To qualify as breast-fed, babies had to be either exclusively given breast milk, or have a maximum of three bottles per week.
The infants were all then followed up to the age of two with regular weight, height and body mass index measurements taken.
At the age of two, there was no difference in height between the groups, but the high protein group were the heaviest.
The researchers suggest lower protein intakes in infancy might protect against later obesity.
The children are being followed up further to see whether those given the lower protein formulas have a reduced risk of obesity later on.
Professor Berthold Koletzko, from the University of Munich, Germany, and who led the study, said: "These results from the EU Childhood Obesity Programme underline the importance of promoting and supporting breastfeeding because of the long-term benefits it brings.
"They also highlight the importance of the continual development and improvement in the composition of infant formula.
"Limiting the protein content of infant and follow-on formula can normalise early growth and might contribute greatly to reducing the long-term risk of childhood overweight and obesity."
But writing in the American Journal of Nutrition, Dr Satish Kalhan of the Case Western Reserve University in Cleveland, US, said: "On the basis of these data, should we consider prescribing low protein formula to infants?
"The answer most likely is a categorical no."
A spokesman for the UK's Infant and Dietetic Food Association said companies had already reduced protein levels to well below those mentioned in the study.
She added: "The scientific evidence reviewing the role of infant formula in the development of obesity in later life is unclear.
"Most studies in this area are short-term and very few look at the long-term effect into adulthood."
But she added: "Clearly further research is required and this is an area we follow closely to ensure that the product we represent are based on generally accepted scientific evidence."
New infant growth charts, to be introduced in the UK this summer, have been changed so they relate more closely to the growth patterns of breast-fed babies.
Existing charts are based on a 1970s study into the growth patterns of formula-fed babies, and many breast-fed babies fall short - often causing concern to their parents and to health visitors.