Today's Kids Are Fat. Why? They Eat More

There’s an epidemic of childhood obesity but no agreement over what’s making kids fat. Is it eating too much junk food or spending too much time watching TV instead of exercising? Scientists have come up with a clever way to answer this question, by figuring out how many calories children and adults actually burn in the course of the day, then comparing that with how much Americans actually eat.

The comparison isn’t perfect; the calorie-burning was figured by actually testing 1,399 adults and 963 children to see how many calories they burn in a day, while the food intake was figured using the national food supply from the 1970s and the early 2000s. Researchers calculated what those adults and children should weigh today, based on the fact that people eat more on average now than 30 years ago. If the actual weights were lower than the projected number, that would mean that people now are getting more exercise than people did 30 years ago. If they weighed more, it would mean they are getting less exercise. 

The adults did weigh less than projected, suggesting that they are getting more exercise than in years past. But children’s weights exactly matched the projected number, suggesting that it's not reduced physical activity that is the culprit in the youth obesity epidemic but rather the increased food intake. According to study author Boyd Swinburn, chair of population health and director of the World Health Organization’s Collaborating Centre for Obesity Prevention at Deakin University in Australia, the results indicate that exercise alone isn’t the solution.

Today’s children eat about 350 calories a day more than did kids in the 1970s, the equivalent of a small serving of french fries and a nondiet soda. Grown-ups eat about 500 calories more–about a hamburger’s worth. You could cut those calories by exercising more, of course, but that would require 150 minutes more of walking each day for a child and 110 minutes for adults. Not too realistic.

What’s more, extra PE time at school doesn’t increase children’s activity levels, according to another study. Instead, children who have more physical education class time tend to lounge more after school, and those who have less PE are more active at other times of the day. This is based on measuring children’s activities with pedometers for a week at a time in four consecutive school terms. Children seem to have an “activitystat” that remains constant for an individual over time. So scheduling more opportunities to exercise might not help fight obesity as much as public health advocates would like. Perhaps taking away those fries is the only option.

Related: I recently wrote about how to protect your child from metabolic syndrome, which can lead to heart disease and diabetes, and my colleague Katherine Hobson explains how Uncle Sam now says kids should exercise one hour a day; try tree-climbing! Here are 5 ways to get more play in your child’s day, plus advice from psychiatrist and play expert Stuart Brown.