Infants raised on formula who are introduced to solid foods before four months of age tend to gain more weight within the first year than infants who start later, a recent study suggests.
But the age at which babies were given solid foods didn't seem to influence much of their longer-term growth.
"It's not about how fast they grow, but whether the children are likely to be overweight," said Dr. Berthold Koletzko, a study co-author who studies nutrition at the Dr. von Hauner Children's Hospital in Munich, Germany. "And they're not more likely to be overweight by two years if they receive solids earlier."
Researchers tracked nearly 700 European infants for two years. Infants between six and seven pounds raised on formula received solid foods starting a little over three months, between three and four months, between four and five months, or six months or later.
Babies who started solid foods at three months weighed less but caught up in growth within six months compared to those who started solid foods at six months and grew slowly within three months.
By two years, there were no differences between groups in weight or length.
Infants eating solid foods also consumed more calories during the first eight months.
Among children born at lower weights, "researchers found an association between lower birth weight and introducing solid foods earlier," said Dr. Lindsey Sjaarda, a researcher at Children's Hospital of Pittsburgh, who was not part of the study.
"It's something that needs to be explored. Recent research seems to indicate that catch-up growth isn't always a good thing," she told Reuters Health.
The study applies to populations in industrialized countries, where "a large fraction of children" have "already been introduced to solid foods before four months of age," according to the authors, not developing countries.
Previous studies have shown conflicting results on whether infants who start eating solid foods earlier are more likely to become obese.
Childhood obesity has tripled over the past three decades, with about 12.5 million American children and adolescents obese, according to a 2007-2008 report from the U.S. Centers for Disease Control and Prevention.
Though Koletzko agreed that children who grow faster will demand more food, and possibly gain more weight, he didn't think they will likely become obese.
He recommended introducing solid foods when a baby shows interest by sitting up and reaching for food or opening their mouths when they see their parents eating. But he cautioned that some infants may need more calories than others.
"At this age, communication happens between infants and parents," he told Reuters Health. "They give a lot of signals to parents. But if the baby is not signaling, don't force it, just wait."