As childhood obesity has increased, researchers have looked for ways to help children reach healthy weights. Does increasing kids' physical activity make enough of a difference?
Well, not really, according to a new study. Researchers followed up with overweight and obese kids three years after originally assessing them.
The researchers found that the kids did improve their weight category a tiny bit if they had a big increase in physical activity. Overall, though, the change was very small.
Physical activity helps, but this study did not offer evidence that it could get rid of obesity by itself.
The study, led by Andrew Trinh, MBBS, of the Centre for Community Child Health at Royal Children’s Hospital and the Department of Pediatrics at the University of Melbourne in Australia, aimed to find out what link existed between children's weight and their level of physical activity.
The researchers tracked 182 overweight and obese children, aged 5 to 10, from 45 general practice offices in Melbourne, Australia. The children's body mass index (BMI) was measured at the start of the study and three years later.
BMI is a ratio of a person's height to weight. It is commonly used to determine whether someone is a healthy weight or is overweight or obese.
The researchers also measured the children's level of physical activity at the start of the study and three years later. The children wore a device for a week that measured their physical activity in "counts per minute" (CPM).
At the start of the study, the researchers did not find any link between the children's BMI and how much physical activity they got.
However, at the follow-up three years later, they did find a small correlation between the two. The children's BMI fell by 0.11 points for every 100 cpm increase in the child's activity level.
That level of change is very, very small. A healthy weight BMI ranges from 18.5 to 24.9, and an overweight BMI is 25 to 29.9. Anything over 30 is considered obese.
The researchers also found that children who increased the time they spent in moderate to vigorous activity were more likely to stay in their BMI category instead of moving into a higher one (such as moving from overweight to obese).
The researchers concluded that "sustained increase" in a child's moderate to vigorous physical activity can improve the child's BMI over three years if the child is overweight or obese.
However, the effect may be extremely small – even when the increase in physical activity is high. They said this small increase "may explain disappointing BMI outcomes of brief primary care interventions targeting physical activity."
The researchers did not look at the children's diet, nutrition, body fat mass or calorie burning in this study. They did say, however, that efforts would have to be broader and more comprehensive in many areas of children's lives to increase overweight children's physical activity enough to have a considerable effect on their BMI.
The study was published January 14 in the journal Pediatrics. The research was funded by the Australian National Health and Medical Research Council.
The European Centre for the Environment and Human Health also receives support from the European Regional Development Fund and the European Social Fund Convergence Programme for Cornwall and the Isles of Scilly. The authors declared no conflicts of interest.