You can read how Dr Susanna Y Huh of the Division of Gastroenterology, Children's Hospital Boston, Massachusetts, and colleagues, carried out their study, in the March issue of Pediatrics, the journal of the American Academy of Pediatrics (AAP). An early edition appeared online on 7 February.
Huh and colleagues studied 847 children enrolled in Project Viva, which has been collecting data on a cohort of children from pre-birth onwards.
The main outcome measure they were interested in was obesity at age 3 years. This was defined as having a BMI (the child's weight in kilo divided by the square of the height in metres) equal to or above the 95th percentile on the standard growth chart for that age and gender.
The researchers also took note of when each child started having solid foods as a baby. They categorized this in three periods, before 4 months old, between 4 and 5 months old, and at 6 months old or later.
They analyzed the data for babies breastfed for at least 4 months (the "breastfed" group) separately from that on babies that were never breastfed or stopped breastfeeding before 4 months (the "formula-fed" group) and adjusted the results to take into account child and mother characteristics, including early infant growth.
The results showed that:
- 568 (67%) of the babies were breastfed and 279 (32%) were formula-fed for at least the first 4 months of their lives.
- 75 (9%) of the children were obese at age 3 years.
- Among the breastfed babies, the timing of solid food introduction was not linked to risk of obesity (odds ratio OR 1.1, with 95% Confidence Interval CI ranging from 0.3 to 4.4).
- Among the formula-fed babies, starting solid foods before the age of 4 months was linked to a six-fold increase in risk of being obese by age 3 years, and this was not explained by rapid early growth (OR after adjustment 6.3; 95% CI: 2.3-6.9).
They also noted that about one in four babies in the US is never breastfed, and about half are breastfed for less than 4 months.
The AAP recommends waiting until babies are between 4 and 6 months old before introducing them to solid foods.
The World Health Organization (WHO) currently recommends that babies be exclusively breastfed for their first six months of life, with "continued breastfeeding along with appropriate complementary foods up to two years of age or beyond".
However, in a recent BMJ study, researchers said while they supported the WHO recommendation of six months exclusive breastfeeding for babies in countries where access to clean water and safer weaning foods may not be available to everyone, they questioned whether waiting so long was right for babies in the UK.
"Timing of Solid Food Introduction and Risk of Obesity in Preschool-Aged Children."
Huh, Susanna Y., Rifas-Shiman, Sheryl L., Taveras, Elsie M., Oken, Emily, Gillman, Matthew W.
Pediatrics, Published online 7 February 2011
Additional sources: American Academy of Pediatrics (press release, 7 Feb 2011), MNT Archives, WHO.
Written by: Catharine Paddock, PhD