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TUESDAY, Oct. 21, 2014 (HealthDay News) -- Infants who quickly add weight and length may be showing a genetic propensity for obesity as toddlers, a new study suggests.
In adults, certain genes have been linked to increased body fat, but the same genes in infants promote proportionate gains in fat and lean muscle, the researchers said.
At 1 year, kids with these genes may be heavier and taller. By ages 2 and 3, however, these genes were linked to excessive weight gain, the investigators found.
"Our findings contribute to the growing evidence that lifelong obesity risk can be predicted at very young ages and hopefully modified by very early changes in lifestyle and diet," said lead researcher Ken Ong, head of the child growth and development program at the University of Cambridge's medical research council epidemiology unit in England.
The conclusions are based on a review of four European studies involving more than 3,000 infants in all.
The researchers zeroed in on 16 gene variations previously linked to obesity and found a connection between rapid growth in infants and weight gain in toddlers.
However, determining whether a given child will be obese based on these findings isn't in the cards, Ong said.
The association found in the study does not prove a cause-and-effect relationship.
"While we see robust effects when looking across the whole population, the effects in any individual are too small for these genes themselves to accurately predict future risks, so the risks are not 'fixed' and there is no point in testing kids to see if they have these variants in their genes," Ong said.
The risk of obesity in any individual is the result of both genes and lifestyle, Ong said. "We should recognize that some people -- those at higher genetic risk -- may have to work harder, but the risk is not just due to genes alone," he said.
The report was published in the Oct. 20 online edition of JAMA Pediatrics.
Dr. Luis Gonzalez-Mendoza, director of pediatric endocrinology at Miami Children's Hospital in Florida, said these specific genes are important to spur growth during the baby's first year when weight and length almost double.
"It's very hard to use that as a predictor of who is going to become obese," he said. "The genetic risk probably doesn't show up until the age of 2 or 3."
Dr. David Katz, director of the Yale University Prevention Research Center in New Haven, Conn., said these gene variations explained only a small amount of the variation in growth rates of the children.
"These same genes were part of our genomes 100 years ago when childhood obesity and adult obesity, for that matter, were quite rare," he said.
The genes may indicate varying degrees of vulnerability, but it's the environment that exploits that vulnerability, he said.
"Unlike our genes, the elements in our culture that encourage obesity can be changed," Katz said.
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SOURCES: Ken Ong, Ph.D., head, child growth and development program, Medical Research Council Epidemiology Unit, University of Cambridge, England; Luis Gonzalez-Mendoza, M.D., director, division of pediatric endocrinology, Miami Children's Hospital, Miami, Fla; David Katz, M.D., M.P.H., director, Yale University Prevention Research Center, New Haven, Conn.; Oct 20, 2014, JAMA Pediatrics, online