Babies who are fed only breast milk for the first three months of life appear to be much more likely to maintain a healthy weight trajectory, with the benefits possibly lasting through to early adulthood, new research shows.

The study, published today in the American Journal of Clinical Nutrition, pooled data from four cohorts – three in Europe and one in Australia – adding up to 6,708 babies.

Babies in all four cohorts had their weight and height measured either once or twice a year until they were six years old.

The data showed three growth trajectories:

• one a consistently normal healthy body mass index (BMI) (55.4% of the participants) over the six years,
• one a rapid weight-related growth in BMI early in life that slowed at around two years of age but remained well above normal through to six years (39.8% of the participants), and
• one a persistent and accelerating weight-related growth in BMI over the six years (4.8% of the participants).

Professor Wendy Oddy, of the University of Tasmania’s Menzies Institute for Medical research, led the Australian section of the study using data from the West Australian Pregnancy Cohort (RAINE Study). She said that after adjusting for several other factors researchers found that babies who had been entirely breast fed in the first three months of life and longer were almost twice as likely to maintain a healthy weight up to six years.

“It is concerning that around 45% of all the children fell into the two categories that experienced this rapid weight-related growth. Even though in most of the children the acceleration in growth slowed down at around 2.5 years of age, their BMI remained high and was still significantly above normal at six years old,” Professor Oddy said.

The collection of data used in the Australian part of the study began more than 20 years ago, which enabled researchers to follow up more than 1,000 children as young adults. They measured weight, height, skin fold and fat mass measurements and found an association between rapid growth at six years and overweight and obesity at 20 years.

The study is the first of its kind to monitor participants at regular intervals from birth, a more robust study design than collecting data about early infant feeding retrospectively. The authors adjusted the study for multiple factors, including babies’ birth weight and gestational age, and mother’s age, BMI, education and whether or not she smoked during pregnancy.

“Our observations indicate that if full breast feeding stops before three months of age, children are at greater risk of becoming overweight, even through to 20 years of age,” Professor Oddy said.

“This adds to the existing World Health Organisation evidence that, if possible, mothers should aim to fully breastfeed their baby beyond three months, and ideally, fully breastfeed until six months and beyond up to two years of age.”