One of the best ways to prevent obesity as an adult is to reverse it during childhood.
Researchers from Harvard and the George Washington University analyzed the health and weight records from more than 41,500 children, teens, and adults in the United States, and used computer modeling to predict rates of future obesity. They predicted that over half of the kids under 20 who are obese—that is, have a body mass index (BMI) of 30—will be obese at the age of 35. Today, about 36% of adults in the US are obese.
More worryingly, the study published (paywall) Nov. 30 in the New England Journal of Medicine found that kids who are obese have a higher risk of being obese as an adult—especially once they hit their teens. A 2-year-old who meets the criteria for obesity has a 75% chance of being obese at 35. That risk increases to an 88% chance if she’s obese at 19—more than three times more likely than kids who were not. For severely obese children who have a BMI of more than 35, the risks are even worse. A 2-year-old with severe obesity has about a 20% chance of having a healthy weight as an adult, and a 19-year-old’s chances decrease to about 6%.
“It seems the excess weight gained in childhood puts kids on a trajectory that persists,” Zachary Ward, an epidemiologist at Harvard and lead author of the study, told Reuters.
The paper didn’t outline why kids who are obese now are likely to be as adults. Although some factors like genetics and the composition of the bacteria in the gut may affect weight, the researchers think that some of the largest factors are habits like diet and exercise.
The good news is, these are both habits that can be taught at a young age: Ward thinks that dietary interventions, like taxes on sugary drinks and setting nutritional standards at school, can help kids maintain a healthy weight. The other obvious moves include encouraging kids to be more active—through good old playing outside, better phys ed at school, or through organized sports (within moderation).
Obesity isn’t necessarily a dangerous health condition, but it does put people at higher risk for more serious problems. People who are obese are more likely to have high blood pressure, heart disease, diabetes, sleep apnea, and some types of mental-health disorders—all chronic conditions that put added stress and can lead to earlier death. On top of these health concerns, it may be harder for people who are heavier to have a healthy body image—a psychological stressor that can bring on some of these health concerns over time.
Keeping kids at a healthy weight early on is one way to lower the risks obesity later on in life. But it’s not a guarantee that kids will always remain a healthy weight: Even teens who aren’t obese at 19 still have a 44% chance of being obese at 35.
Which means you’re never too old to try to eat more vegetables and get outside to play.
Read next: The case for adult recess