Can Your Family Make You Obese?

New research reveals parents' impact on childhood weight, even in rich families.

We often talk about obesity as a public health crisis, but rarely about how totally, utterly baffling it is as a disease. Obese people face discrimination at almost every turn, and yet the American obesity rate is now over 27 percent, and rising. It's an extremely expensive condition—the severely obese spend more than twice as much on medical care—but it's also most prevalent among low-income people.

So, why does it keep spreading?

It’s a sensitive issue, but the more we learn about how obesity works—and doesn’t—the better we can help those affected by it.

Recently there’s been some surprising new research on obesity’s origins. One new finding debunks the idea that grocery stores are a panacea for “food deserts” and their attendant health problems. A new study in Health Affairs found that after a new grocery store came to a Philadelphia food desert, only about a quarter of residents began using it as their primary food-shopping source, and those who did use it didn’t lose weight or eat more produce.

And it turns out obesity might start even earlier than previously thought: Another study found that overweight five-year-olds were four times more likely to be obese by the age of 14 than children who started kindergarten at a normal weight. So much for promoting high-school gym class; some kids are already riding toward diabetes on their training wheels.

To make matters worse, a recent meta-analysis published in Pediatrics found that two-thirds of parents underestimate the BMIs of their children, especially when their children are overweight or obese.

“They’re in denial,” the study’s lead author, Alyssa Lundahl, told the New York Times.

2004 study in the Journal of Pediatrics found that the biggest factor that predicted overweight in children was if the parents were also overweight. But it turns out that even very subtle shifts in family structure are correlated with higher rates of obesity in children, regardless of the parent's own health status.

The problem? None of these family studies point to a clear cause or solution. Past research has suggested that single-parent households increase the likelihood of obesity in children—but mainly just in girls. And children are more at risk of obesity in single-mom households, but more so if the mother is not well-educated.

To untangle some of these trends, a March study published in the Journal of Applied Research on Children looked at a sample of 10,400 children, their BMIs, and the structure of their households. The results were basically a web of contradictions. They're enough to make any health-conscious parent wary of getting a divorce, remarrying ... or really doing anything other than residing in a nuclear, sitcom-family formation:

  • Children raised by two co-habitating biological parents had the highest rates of obesity, at 31 percent.
  • But if those parents were married, the children had one of the lowest obesity risks, at 17 percent.
  • Children residing with an adult relative had a high (29 percent) likelihood of becoming obese.
  • But if that adult was their single father, they had a very low risk—just 15 percent.
  • And strangely, the children of single mothers and those of co-habitating (not married) step-parents had similarly high rates of obesity, at 23 percent.
Journal of Applied Research on Children

The authors point out that some of these family configurations are simply more likely to occur in poor people, more of whom experience the stress, long hours, and living conditions that breed obesity. For example, mothers in the sample who were married to the children’s biological father were also more likely to be older, more educated, more likely to be white, and less likely to be poor than the others.

So the authors went a step further and took out the poverty variable. What happened next was even more surprising—and head-scratching: “Non-poor children living with married step-parents had a 67 percent higher risk of obesity compared to similar non-poor children raised by married biological parents.”

Simply coming from a combined family somehow made the children more than two-thirds more likely to have weight problems.

Meanwhile, poor children living with either a single father or a step-father were less likely to be obese than their rich peers with two biological, married parents. So even though "broken" families come off badly in the study, they seem to protect against obesity in some cases.

We can only speculate on the reasons behind all of these relationships. The authors throw out a few possibilities: That step-families might have to ferry kids to and from different households and thus have less time for meal planning and exercise. They also suggest that perhaps blended families have more resources, and are therefore more likely to own video games and other toys linked to inactivity. Or maybe they monitor their children less aggressively so their offspring are more likely to gorge on snack foods.

The study author told me that she later explored 11 possible reasons for these disparities, but "nothing seemed to explain why children in married parent households had lower probabilities of obesity."

One thing is clear from this sweep of findings: Obesity has roots in childhood, families impact their children’s weight in significant ways, and, most frightening of all, we have no idea exactly how.