Infants who see rapid growth in the first six months of life may be at a significantly higher risk for obesity later on, according to a Harvard study published in the April issue of Pediatrics.

These results imply that obesity can be rooted in the very early stages of life, according to Elsie M. Taveras, the study’s lead investigator and an assistant professor at the Medical School.

“Some think, ‘oh, it’s just baby fat, it’s cute, it’ll go away,’” Taveras said. “Our results will be surprising to people who thought there are no consequences for a chubby baby.”

Taveras said she understands that, upon learning the results of the study, parents would immediately begin worrying that their children were growing abnormally.

“I’d recommend that mothers not necessarily worry,” she said. “These are questions for the pediatrician to determine.”

The main implication of this study is that rapid weight gains early in life are significant and are associated with later obesity, according to Sheryl L. Rifas-Shiman, a research associate at Harvard Medical School and one of the article’s authors.

“[Early life] might be a critical period that health professionals and researchers should focus on,” said Rifas-Shiman.

Although previous studies have found evidence linking rapid weight gain in infancy to a greater risk of obesity later in life, this study analyzed growth rate more precisely, monitoring weight-to-length ratio over the first six months.

According to Taveras, the weight-to-length ratio, akin to the body mass index in adults, is a more accurate indicator of body fat than weight alone.

The study showed that rapid rises in weight-to-length ratio increased the risk of later obesity from 20 to 40 percent, a risk Taveras called “not insignificant.”

Clifford W. Lo, an assistant professor of pediatrics at the Medical School, said he saw “several ramifications” of the study’s results.

“Something is happening within the first year or two of life that has long-term effects,” said Lo, who is also an assistant professor of nutrition at the School of Public Health.

The next step for researchers, Taveras said, is to isolate the cause for the sort of rapid infant growth that can cause problems.

“It could be overfeeding, it could be factors that arose before the child is even born, it could be genetics,” Taveras said. “We don’t have all the answers for parents yet.”

The recently-published study, funded by the National Institutes of Health, was conducted by researchers from Harvard Medical School, Harvard Pilgrim Health Care, and Harvard-affiliated Children’s Hospital in Boston.

The data from 559 mother/child pairs used in the study was collected from a subgroup from Project Viva, which has been following over 2000 pregnant women recruited in the first trimester of their pregnancy since 1999.

—Staff writer Helen X. Yang can be reached at hxyang@fas.harvard.edu.