As a pediatrician with a special interest in working with overweight children and their families, I frequently talk with families about how to help the kids achieve and maintain a healthy weight. In many cases, it comes down to not gaining any weight as the child grows in height. Then, body mass index (BMI) is likely to normalize and we can avert many of the health problems associated with obesity. Of course, this requires changes to family habits and patterns around nutrition and physical activity, but it is a relief to families that most overweight kids do not actually need to lose weight.While I have thought this to be true—that maintenance of weight during increases in height will decrease BMI and help a child achieve a “healthy weight”—I’ve always talked about it in a “general” way, without having hard numbers to say just how many fewer calories a child needs to eat to be able to actually maintain that weight. Or for whom this strategy works best. But now we have the research that will enable me to be much more specific.The ScoopIn late July 2013, a study was published by researchers from the National Institutes of Health, which shared results of a (complex) mathematical model that was able to predict a lot about kids’ weight, including how many fewer calories a child of a certain age needs to consume to maintain weight.Here are a few key findings:Today’s kids, on average, eat a lot more calories than kids from a generation ago. For example, the average 10-year-old boy eats about 300 calories per day more than his parents did when they were 10. Kids who are obese eat a lot more calories than their healthy-weight peers. In fact, from ages 5-11 years, obese boys eat, on average, 750 calories per day more than healthy-weight peers; for girls the difference is 850 calories. The well-touted formula that 3,500 calories = 1 pound of fat does not hold true for kids. The authors use an example of a 10-year-old female who was of normal weight at 5 years of age, but by age 10 was 4.5 pounds overweight. Using the standard formula of 3,500 calories in 1 pound, one would suppose she needed to consume an extra 15,750 calories to gain that amount of weight (4.5 X 3500) (that would end up being about 40 excess calories per day). Not so. Rather, she consumed an extra 157,000 calories too many in the five years to gain that amount of excess weight (400 calories per day)! (Once kids stop growing, the adult equation is more likely to hold true.) Kids who are at a period of peak growth (roughly 10-15 years in boys and 9-13 years in girls) can achieve a healthy BMI by maintaining weight. The study found that 11-year-old obese boys who maintained their weight from 11-16, had normalized BMI and lost a lot of body fat, while increasing their lean mass. (Unfortunately, this didn’t work out as well for girls, possibly because the age range measured (11-16yrs) occurred during a period of slower growth potential than for the boys.) And, finally, the model had the formula that I was looking for: The amount fewer of calories to consume each day for a child to maintain weight while growing in height:Boys: (68 – 2.5 x age)/2.2 x #lbs overweight.So, for a 10-year-old boy who is 10 pounds overweight, to maintain his weight, he needs to decrease his current calorie intake by 200 calories per day.Girls: (62 – 2.2 x age)/2.2 x #lbs overweightSo, for a 8-year-old girl who is 15 pounds overweight, to maintain her weight, she needs to decrease her current calorie intake by 300 calories per day.What healthsite ThinksKids are a lot more resilient to gaining too much weight than we thought! This is both good news and bad news. It is good because it helps a worried parent of kids who spend too much time loading up on sugar with the grandparents, for example, some relief that the kids will be ok. It takes a much longer period of time of calorie over-consumption to gain too much weight. It’s also great news for overweight kids who haven’t yet gone through their growth spurt, especially boys. In many cases, they don’t need to lose weight; they simply need to slow weight gain as they gain height. But here’s the bad news—the reality is we suffer from an epidemic of childhood obesity. This didn’t occur overnight. Today’s kids have been subject to ongoing, long-term overeating and under-exercising compared to kids of a generation ago. We need to make substantial changes in the societal norms of how much is appropriate to eat and the amount of physical activity our kids get on a typical day.What It Means to YouAs a parent, what is the main take-away? Pay attention to how much your kids eat and how much physical activity they get in a day. And, if you are the parent of an overweight child, discuss this with your child’s pediatrician and develop a plan to make healthy changes in nutrition and activity—and focus less on the scale.