Tuesday 22 October 2019

Somebody should measure childhood obesity

The government has set up a National Food Strategy, led by Henry Dimbleby, and has launched a call for evidence which closes on Friday.

The National Food Strategy will examine activity across several departments of state, building on the flagship Agriculture Bill and Fisheries Bill currently before Parliament, the Industrial Strategy, the Childhood Obesity Plan and the upcoming Environment Bill.

With regards to the Childhood Obesity Plan, I have just submitted a proposal suggesting that maybe, just maybe, somebody should make an attempt to measure childhood obesity.

Here's what I wrote...

The NFS call for evidence mentions the government’s Childhood Obesity Plan. The Childhood Obesity Plan opens with the assertion that ‘more than one in three children are obese or overweight by the time they leave primary school’. The claim that more than a third of eleven year olds are overweight or obese is routinely made by the Department of Health, Public Health England and single-issue campaigners, and is used to justify a wide range of interventions in the food market.

This factoid is rarely challenged, but it should be. We have no idea what the rate of childhood obesity is in the UK because nobody has made a serious effort to measure it. All we can say with confidence is that it is far lower than the government claims. For reasons that have never been explained, the government refuses to use the clinical definition of childhood obesity (based on the BMI of the 98th percentile in 1990). The clinical definition sets an unrealistically low threshold and therefore allows many false positives, but the government’s definition (based on the BMI of the 95th percentile in 1990) allows the category to consist mostly of false positives. Most of the children who are classified as obese by the government’s definition would not be classified as such by a clinician - or, indeed, by a lay person.

If the UK government used the clinical definition, it would find that the rate of obesity among eleven year olds was well under five per cent. If a representative sample was examined by a clinician, the rate would likely be lower still. It is bizarre that so much time and money is directed at the problem of childhood obesity without any serious attempt to measure its prevalence. Politically, it is easy to see why campaigners prefer a large number to a smaller number, but this does not justify fiddling the figures.

The inflation of the childhood obesity figures leads to demonstrable absurdities. For instance, it is well understood that the risk of obesity rises with age. If taken at face value, the government’s statistics show that the prevalence of obesity among 13-15 year olds is 25 per cent, but falls sharply to 15 per cent for 16-24 year olds. Children do not suddenly lose weight when they leave school. The discrepancy is explained by adult obesity being measured objectively while childhood obesity is not.

Given the Department of Health’s apparent lack of interest in getting to the truth of this matter, it would be a suitable target for fresh thinking from the National Food Strategy. Creating realistic BMI charts to measure childhood obesity is an achievable and important goal.

It is extraordinary to consider that the definition of childhood obesity was made without any child ever being examined or diagnosed (instead, the rate of obesity among children was extrapolated from the rate of obesity among 18 year olds!). A more rational approach, which would cost a tiny fraction of Public Health England’s £4 billion budget, would involve clinicians examining children of various ages and recording the BMI of those who are at the lower end of the obese range, based on adiposity and visible excess weight. These records could then be used in perpetuity as thresholds for childhood obesity at different ages.

Aside from being truthful with the public, a realistic measure of childhood obesity would have two benefits. Firstly, it would allow policy to be targeted towards children who are genuinely obese, as opposed to statistically obese, by giving us accurate information about their profile (socio-economic characteristics, region, race, etc.).

Secondly, it would allow progress to be measured. At it stands, the government’s target of reducing childhood obesity by 50 per cent by 2030 can only be achieved if large numbers of healthy children lose weight. This is neither realistic nor desirable. Officially, the proportion of children who are obese has remained more or less unchanged since 1999. Thanks to the large number of false positives, it is impossible to tell from the official dataset whether the number of genuinely obese children has risen, fallen or remained the same. 

I have written about this at greater length (with links to sources) in these two articles:



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