Researchers feel that, healthy infants breast-fed uniquely for the first three months of life grow faster than their formula-fed peers, but there are no differences in weight, length or head circumference between the two groups by the time they reach the age of one year.
The findings contradict research that suggests infants who are fed only breast-milk for the first year of life gain less weight than babies given at least some formula. These studies have ignored other factors that might influence a baby's growth and development and the mother's decision to breast-feed exclusively.
For instance, babies that grow very quickly may tax their mother's milk supply, causing her to supplement. Alternatively, breast-fed infants who are not growing quickly may be supplemented with formula in an attempt to spur their growth, Dr. Michael Kramer from McGill University in Montreal, Canada, and colleagues, suggest.
To investigate, the researchers followed a group of more than 17,000 healthy infants weighing at least 5.5 pounds and born in the Republic of Belarus. Weight, length, and head circumference, a gauge of brain development, were measured at 1, 2, 3, 6, 9 and 12 months. Some infants were born in "baby friendly" hospitals that encouraged exclusive breast-feeding, and others were born in hospitals that did not promote breast-feeding.
More than 43% of infants born in baby-friendly hospitals were breast-fed exclusively at 3 months of age, compared with less than 7% of infants born in the other hospitals. And while there were no differences in weight, length and head circumference at birth, infants breast-fed exclusively weighed more and grew faster by 1 month, and continued to gain weight at a faster rate than their formula-fed counterparts through the third month.
In an interview ,Kramer said that the faster weight gain among exclusively breast-fed infants may reflect a biological effect from the contents of breast milk, but added that the long-term significance to a child's health are not known.
By 12 months, all infants were similar in weight, length and head circumference, and conformed to standards set by the World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC). Infants weaned in the first month were falling behind in their growth, the study also found, but the decision to switch these infants to formula appeared to have been based on their slow growth.
"Our results offer no support to the prevailing premise that prolonged and exclusive breastfeeding inexorably leads to deficits in weight and length during the first year of life," the study concludes. The American Academy of Pediatrics, WHO and UNICEF recommend that mothers breast-feed their infants for the first year of life. A number of studies indicate that breast-feeding can lower the risk of infections and allergies, possibly into adulthood, and may boost brain development early in life.