Pam Levin's daughter weighed less than 5 pounds at birth. But by the time the child turned 3, Levin and her husband had begun to bristle at some of the comments about her. "People would say, 'She's chunky' or 'She's a big girl,'" Levin says.
The comments may not have been tactful, but the Los Angeles mom caught herself wondering if they were true. Was the adorable, easygoing preschooler overweight? During the child's first year of life, she had been smaller than 95% of children her age, according to pediatric growth charts, weighing about 17 pounds on her first birthday. But her weight had increased, and kept increasing, until she was 43 pounds at age 3 1/2.
"All of a sudden she's was on the 50th percentile, then the 75th, then 99th," Levin recalls. "You say, 'Wait a minute. Something's not right.'"
Today, one of every three U.S. children is overweight -- but it's much easier to prevent obesity than to treat it. That's why pediatric obesity experts now say intervention should begin early -- very early. The risk of becoming overweight or obese, it increasingly seems, begins before a child is born, establishes roots in infancy and may be entrenched by the time a tot starts kindergarten.
In recent studies, researchers concluded that some risk factors for childhood obesity exist even before birth. Further, they've found, obese 3-year-olds already show the signs of inflammation that is linked to heart disease in adults.
The notion that a person's lifelong weight trajectory might be programmed early in life is startling -- and potentially revolutionary, says Dr. Nicolas Stettler, an associate professor of pediatrics and epidemiology at the University of Pennsylvania.
"If we can identify a short period of time where an intervention can have a long-lasting effect, that could be very promising," he says.
So far, most of the evidence that the early years affect weight into adulthood comes from observational or epidemiological studies. There are few randomized, controlled trials -- the most scientifically rigorous kind that prove cause and effect, says Dr. Elsie M. Taveras, an assistant professor of population medicine and pediatrics at Harvard Medical School. But she points out, "We have pretty strong observational studies for a good number of risk factors in the prenatal, infancy and early childhood period."
In her paper, published March 1 in the journal Pediatrics, Taveras and her colleagues summarized more than one dozen factors in the prenatal period through age 5 that can increase the likelihood of later obesity. The research was based on a study of 1,826 mother-child pairs from pregnancy through the child's first five years of life.
Many were behaviors that are often passed down through generations and are more likely to be found in black and Latino families than in white families, possibly accounting for the high rates of obesity in those communities. For example, black and Latino infants are more likely to be fed solid food before 4 months of age and to sleep less as infants.
Each of the three early-life stages -- prenatal, infancy and early childhood -- comes with its own risk factors. But each also comes with the chance to intervene, breaking a lifetime cycle of obesity and dieting before it starts.
Several risk factors likely begin with the mother -- even before she's a mother.
Almost half of U.S. women today begin pregnancy overweight or obese, automatically increasing the likelihood that their babies will be born either too small or too large, both of which increase the risk of obesity for the child later in life.
Further, studies show that how much weight a pregnant woman gains and whether she develops gestational diabetes both can influence her child's weight in adulthood.
The odds of being overweight at age 7 were 48% higher for children of women who gained more weight than recommended during pregnancy compared with women who met weight guidelines, according to a study by Stettler and colleagues published in 2008 in the American Journal of Clinical Nutrition.
"What we find is that these things set up children for a lifelong risk of obesity," says Asheley Cockrell Skinner, an assistant professor of pediatrics at the University of North Carolina School of Medicine. "These factors don't just make them overweight; they become barriers to helping them change when they get older. It becomes the story that never ends."