There has not been a peep in our news about this story, nor about the results of a number of recent clinical trials in Britain that have tested childhood obesity prevention programs based on increasing activity levels in children. The results are not surprising to those who understand the physiology of the development of body sizes, but probably sound unbelievable to anyone who’s relied on mainstream media for their information. The BBC News reported:

Obesity study “needs more funds”

The EarlyBird programme in Plymouth has won acclaim after tracking the development of hundreds of children. Its findings fundamentally challenge the government's strategy to prevent obesity by raising activity levels.

Researchers taking part in the study, based at Derriford Hospital, are painstakingly mapping the development of more than 300 children from across the social spectrum....Every year the children are fitted with accelerometers, which record activity over the course of a week. They are worn around the waist like pedometers, measuring movement ten times a second.

The BBC story exampled two pre-teen girls, one a long-distance runner active in local track and another who hates sports and loses her breath when she tries to exercise. But the researchers found that the overall activity level of the second girl is actually higher than the girl perceived as more active!

Dr. Terence Wilkin, M.D., FRCP, FRCPEd, professor of Endocrinology and Metabolism at Peninsula Medical School, Plymouth, and Early Bird program director, said the reason is because the amount of activity children get is genetically set and has nothing to do with sports or structured physical activities.

"Those children who had little opportunity at school to undertake activity were bouncing around after school whereas those who'd had a lot of opportunity during the course of the school day settled down, and did relatively little," he said. "The most important thing (was) if you added the in-school activity to the out-of-school activity, they were exactly the same."

That is not the only surprise. Professor Wilkin said children's activity levels had no bearing on their body mass index - their risk of obesity. "Even looking over a period of years, because we repeat these measures year by year in these children, we have been unable to show any relationship between the physical activity that a child undertakes and his BMI." ...[T]hese findings cast serious doubts on the government's strategy to halt the increase in childhood obesity by the end of the decade, largely by encouraging physical activity. Professor Wilkin said it was based on unproven prejudice - that today's children do not exercise as much as previous generations.

The body of evidence has consistently shown that no physical activity-based childhood obesity intervention effort — no matter how intensive, comprehensive or long-lasting — has ever been able to show a reduction in childhood obesity rates. Not here, not anywhere. Last October, for example, the results of another randomized controlled trial were reported in the British Medical Journal. While children in 36 preschools in Glasgow, Scotland, engaged in physical activity programs in school plus home-based health education aimed at increasing physical activity through play and reducing sedentary activities, after one year, there was no significant effect on reducing body mass indexes among the children.

Dr. Wilkin and other doctors from Penninsula Medical School wrote in the British Medical Journal that claims that the amounts of physical activity just need to be further increased in duration or intensity before BMIs can be affected are an unproven hypothesis.

[T]here is an alternative, possibly more compelling, explanation – that the physical activity of children is regulated internally by an ‘activitystat’, and not externally by opportunity. There is a growing literature to support the ‘Activitystat Hypothesis’....

The Activitystat Hypothesis has been tested both in and out of school. In a study of more than 200 children wearing MTI accelerometers in three schools providing very different opportunity, school one provided 9.0 hours per week of timetabled PE, school two provided 2.2 hours and school three 1.8 hours. Activity in school was greater among the children attending S1 compared with S2 or S3, but the reverse was true out of school, such that total daily activity was the same for all three (difference less than 0.3%). Indeed, <1% of the four-fold variation in activity of the children could be explained by the five-fold variation in opportunity provided.

In a second study, the energy cost of being driven to school amounted to 16% during the hours of the ‘school run’ (8-9am and 3-4pm), but total activity was the same between those who walked and those who did not (difference less than 0.1%). Again, the difference was made up at other times during the week.

These two studies, and other data reported by the EarlyBird study, suggest that the activity of children follows a set-point that is individual to the child. The four-fold range of activity observed among young children appears to represent their range of set-points, not their environments. Most activity is unstructured, and children seem to use it to compensate for the impact of structured or imposed activity. It is important to recall that many studies are able to show a temporary rise in physical activity following exercise intervention that does not last long- term, nor once the intervention has been withdrawn. ....

While the evidence has continued to not support the effectiveness of popular physical activity programs believed to "prevent childhood obesity," calls for more and bigger programs, and more funding for them, do continue.



© 2007 Sandy Szwarc