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By any measure, mother-child bonding is an ideal worth striving for, but new research underscores its importance, finding that toddlers who aren't securely attached may have a greater risk of being obese before they even start kindergarten.

Researchers at Ohio State University and Temple University crunched data from 6,650 U.S. children born in 2001 who were evaluated at age 2 and again at 4 ½ years. When the children were 24 months old, researchers spent two hours observing them interact at home with their mothers. Among the 45 behaviors evaluated: could upset children be comforted through contact with their mothers? Did the children seek out hugs and physical touch from their mothers?

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The children who scored the lowest at 24 months were deemed "insecurely attached;" when researchers calculated their body-mass index, they found the insecurely attached children were 30% more likely to be obese by age 4 ½, according to the study, which was published recently in the journal Archives of Pediatrics & Adolescent Medicine.

Researchers controlled for a host of other factors, including eating habits and maternal health, but nothing else could account for the significant link between emotional security and weight.

In fact, when considering only each child's attachment security score and future weight, the study found that the emotionally insecure toddlers had a 48% greater chance of being obese at 4 ½. Of the toddlers judged to be insecurely attached, 23% were obese at 4 ½ compared to 16.6% of securely attached children.

The findings indicate that it may be time to expand our understanding of the causes of childhood obesity: being an overweight kid may be about far more than portion size and healthy food. Other research has shown that stress and an exaggerated stress response can disrupt the body's ability to regulate body weight. Considering that children's ability to regulate their emotions and respond to stress is formed early in childhood based on their interactions with their caregivers, scientists hypothesized that children who are insecurely attached are at higher risk for obesity.

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"The same areas of the brain regulate stress response and appetite control, so if a child is stressed because he's not being attended to, it's more likely he will be obese later on and will also use food as a way to respond to stress," says Sarah Anderson, an assistant professor of epidemiology at Ohio State University and the study's lead author.

A securely attached child feels confident that her caregiver will respond quickly, allowing her to explore and seek out new experiences. Insecurely attached kids, on the other hand, may shy away from interaction with others and respond angrily or with anxiously to stressful situations.

The study did not look at whether the elevated rates of obesity persisted beyond the pre-kindergarten year. "We know that children who are obese tend to remain obese, which is one reason why it's important to look at obesity prevention," says Anderson. "It's hard for all people to lose weight, so that's why it's good to prevent it rather than treat it."

Anderson says her study is directed more at policy-makers than parents, but that doesn't mean moms and dads shouldn't take note.

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"I can say from my reading of the obesity research literature and child development literature that there are a lot of good reasons why it's important for parents to consider how they can help their children to develop good capacities for emotional regulation," says Anderson. "I can feel very comfortable saying that this is not harmful. And if it prevents obesity, so much the better."

• Bonnie Rochman