New research from the UK suggests that physical inactivity in children is the result of obesity and not the other way around, challenging the popular view that getting overweight children to exercise more is the key to preventing the childhood obesity; the researchers maintain the path to childhood obesity is set very early in life, long before children go to school and is linked to early feeding habits.

These are some of the findings of the EarlyBird Diabetes Study, which is based at the Peninsula Medical School in Plymouth and has been following a cohort of city school children for 11 years.

You can read a paper on it in an early issue of the journal Archives of Disease in Childhood, published online on 23 June.

The director of the EarlyBird study, and lead author of the report , is Dr Terry Wilkin, Professor of Endocrinology and Metabolism at the Peninsula Medical School and Consultant Endocrinologist to the Plymouth Hospitals NHS Trust. He and his colleagues were intrigued by the results of a 2009 review of trials of physical activity to reduce childhood obesity that found weight loss was just 90g (3 oz) over 3 years. Why were the trials so ineffective, they asked?

While we all know that overweight children tend to do less exercise, this does not necessarily mean, as many of us might assume, that it is inactivity that leads to obesity, it could be the other way around, and Wilkin and colleagues set out to find some evidence for this and ask the “chicken and egg” question: What came first? Does lack of physical activity precede the changes that lead to fatness in children, or does increasing fatness in children precede changes in physical activity?

By examining the data they had collected over 11 years on over 200 children recruited from 40 Plymouth primary schools, they concluded unequivocally that physical activity had no effect on weight change, but weight change led to less physical activity.

For the study, they examined data on 202 children (25 per cent were overweight or obese, and 53 per cent were boys). The main outcome measures were physical activity and percentage body fat, measured every year.

To measure physical activity, the researchers fitted each child with an Actigraph accelerometer, which they wore for 7 consecutive days once a year. This yielded two measures for analysis: volume and intensity. Thus the researchers could see the total volume of physical activity, and the time the wearer spent doing moderate and vigorous activity.

For the body fat measure the children underwent annual x rays (the method used was dual energy x ray absorptiometry).

When the researchers analysed the results, they found that:

  • Percentage body fat was predictive of changes in physical activity over the following three years.
  • Physical activity was not predictive of subsequent changes in percentage body fat over the same follow-up period.
  • A 10 per cent higher body fat percentage at age 7 predicted a relative decrease in daily moderate and vigorous intensities of physical activity (4 min from 7 to 10 years of age).
  • But more physical activity at age 7 did not predict a relative decrease in percentage body fat between 7 and 10 years of age.

The researchers suggested that children who become overweight may lack confidence and feel embarassed about how they look and this stops them taking part in sporting activity and exercise.

They also suggested that overweight children might find exercise discomforting, making them feel pain earlier than normal weight children.

Wilkin and colleagues concluded that:

“Physical inactivity [PA] appears to be the result of fatness rather than its cause.”

“This reverse causality may explain why attempts to tackle childhood obesity by promoting PA have been largely unsuccessful,” they added.

The implications of this study are very important for public health policy, because it implies that the physical activity of children, which is vital for their fitness and general wellbeing, may never improve unless childhood obesity is tackled first.

A press statement from Peninsula Medical School suggests that EarlyBird has already shown that the paths leading to obesity in childhood are set very early in life, long before children go to school, and that in many cases, obese children are often offspring of an obese same sex parent.

The study suggests that calorie reduction, rather than physical activity, appears to the key to weight reduction in overweight and obese children, pointing to early feeding errors, and the contribution of “portion size, calorie-dense snacks and sugary drinks”.

Other findings from EarlyBird include:

  • Many parents of obese children seem unaware and unconcerned.
  • Children’s inactivity is not due to lack of green spaces and sport centres.
  • Social inequalities are no longer a major factor: all children are at risk.
  • Healthy weight for life starts at birth (eg do not overfeed low birth weight babies, they are most at risk of later weight gain).
  • Obese mothers breed obese girls and obese fathers breed obese boys: it may be more effective to target the obese parent than the obese child.
  • Girls are naturally more insulin resistant than boys, and therefore at greater risk of type 2 diabetes.
  • Type 1 and Type 2 diabetes are essentially the same disorder of insulin resistance, differing only in rate of progress: keeping weight down should help prevent, or at least delay, the onset of both type 1 and type 2 diabetes.

Perhaps one of the most controversial findings from the overall study is that the average child is no heavier than 25 years ago, suggesting the majority of children have not changed in a generation, that the rise in obesity is confined to a small group, and there may be no widespread childhood obesity epidemic.

“Fatness leads to inactivity, but inactivity does not lead to fatness: a longitudinal study in children (EarlyBird 45).”

Update, June 2013 – In the UK, four times as many hospitalizations caused by a childhood obesity-related problem occurred in 2009 compared to 2001.

B S Metcalf, J Hosking, A N Jeffery, L D Voss, W Henley, T J Wilkin.
Arch Dis Child, Published Online First: 23 June 2010

Additional sources: Peninsula Medical School, EarlyBird.

Written by: Catharine Paddock, PhD