Obesity is set to become the new normal in America.
By the time today's kids reach the age of 35, 57% of them will be obese, a new study predicts. That means that if present trends continue, an American child's chances of having a normal weight when they grow up — or of being merely overweight — are less than even.
The kids who are destined to become obese are not necessarily obese right now — in fact, most of them are not. The Harvard researchers who came up with these projections say that only half of these kids will be obese when they are 20 years old, while the other half will become obese during their 20s or 30s.
The study results, published in Thursday's edition of the New England Journal of Medicine, suggest that health experts have missed the big picture when it comes to childhood obesity.
"Our findings highlight the importance of promoting a healthy weight throughout childhood and adulthood," the researchers wrote. "A narrow focus solely on preventing childhood obesity will not avert potential future health damage that may be induced by the ongoing obesity epidemic."
The team, led by Zachary Ward, a decision scientist at the Harvard T.H. Chan School of Public Health, set out to answer a very specific question.
"We wanted to predict for children now at a certain weight and certain age, what's the probability that they will have obesity at the age of 35?" explained Ward, who is working on his PhD.
They picked age 35 because that's when the health problems associated with obesity — including diabetes, high blood pressure, heart disease and some types of cancer, to name a few — typically begin.
The team's question may sound straightforward, but getting the answer wasn't.
Ward and his colleagues needed growth charts that tracked changes in people's height and weight over decades, starting in early childhood. These charts did not exist. And even if they did, they'd be out of date because the factors that influenced today's adults when they were children wouldn't necessarily apply to today's kids.
The researchers got around these problems by stitching together data from five big studies that took height and weight measurements of more than 40,000 Americans multiple times over many years.
For instance, they might start with a boy who was tracked between the ages of 2 and 10. Then they'd look for another boy with the same racial and ethnic background whose height and weight were similar at age 10 and track him through age 18. At that point, they'd find a man from the same demographic group with similar height and weight at age 18 and follow him until age 25. And so on.
By repeating this process over and over, the team could simulate a complete growth trajectory for a single person who was subject to recent environmental influences.
Ultimately, the researchers wound up with a "virtual population" of 1 million kids and teens who were representative of the nation's actual kids and teens. They used a variety of statistical methods to make sure that their simulations were accurate.
Only then were they able to find answers to their initial question.
They found that at any age, kids who are obese are more likely than their non-obese peers to be obese at age 35. They also found that older obese kids are more likely than younger obese kids to still be obese on their 35th birthday.
For instance, a 2-year-old who is obese has a 75% chance of being obese at age 35, the researchers calculated. But a 19-year-old who is obese has an 88% chance of being obese at age 35.
Likewise, a person who is not obese at age 2 has a 58% chance of being obese by 35. But a 19-year-old who is not obese faces only a 44% chance of being obese by 35, the study authors found.
Compared to a 2-year old who is not obese, a 2-year-old who is obese is 30% more likely to be obese on her 35th birthday. By age 19, the risk of being obese at 35 is nearly twice as high for an obese teen than for her non-obese counterpart.
Not surprisingly, the heaviest children face the greatest risk of being obese adults. A severely obese 2-year-old faces a 79% chance of being obese at age 35, while a severely obese 19-year-old has a 94% chance of being obese at 35.
Just as in the real population, the risk of obesity in the virtual population varies according to race and ethnicity. By age 2, African American and Latino children are more than twice as likely as white children to be obese. Those disparities follow them through adulthood.
The only kids who face better-than-even odds of not being obese by age 35 are those who currently have a healthy weight, according to the study.
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