Saturday, 6 March 2021

That World Obesity Federation scatter plot

It was World Obesity Day recently so we got the inevitable press release from the World Obesity Federation, with the inevitable COVID-19 tie-in. 
The media picked up on one striking claim in particular...
Obesity warning as report shows nine out of 10 COVID-19 deaths have been in countries with high rates of obesity
The correlation cited in the report is actually with overweight, not obesity, but journalists nearly always get those two mixed up. Obesity is a risk factor for COVID-19 mortality, especially morbid obesity. Being overweight, not so much. 

Nevertheless, the claim is that 90 per cent of COVID-19 deaths have taken place in countries where more than 50 per cent of the population is overweight. The, er, 'correlation' between the two is shown in the WOF report in a graph that is the stuff of statisticians' nightmares.

I'm not quite sure where the trend line is meant to go there.

For those who are still not convinced, we were given some examples of countries with low rates of obesity and low rates of COVID-19.

Author of the report Dr Tim Lobstein, who is a senior policy adviser to the World Obesity Federation and visiting professor at the University of Sydney, said: "We now know that an overweight population is the next pandemic waiting to happen.

"Look at countries like Japan and South Korea where they have very low levels of COVID-19 deaths as well as very low levels of adult obesity."

The Guardian reported... 

Among countries where more than half the adult population is overweight, Belgium has the highest level of deaths, followed by Slovenia and the UK. Italy and Portugal are 5th and 6th, while the US is 8th.

Vietnam, by contrast, has the lowest lowest level of overweight in the population and the second lowest Covid death rate in the world.

But these Asian countries didn't have many deaths because they didn't have many cases. Unless the WOF is claiming that being slim stops you catching and spreading the virus, these examples are meaningless. 

If you look at the maps from the WOF report, you can see that the countries with low Covid mortality are nearly all in Asia and Africa. The death rate is low in these countries because they had low infection rates (China, Vietnam, etc.) and/or a young population (India, most of Africa). Obesity had, at best, a marginal impact.

I wrote a quick letter to the Times about this. 

Sir, Tim Lobstein says “there is no escaping the clear correlation between some of the world’s worst Covid death rates and worst obesity rates”. The correlation may be clear, but we should not infer causation from the fact that 90 per cent of Covid-19 deaths take place in countries where more than 50 per cent of the population is overweight. The lowest death rates have been in places that have controlled the virus, such as Vietnam and Japan, or have a young population. In India, only 5 per cent of the population is aged over 65. In Africa, the average age is 20. Such places have had relatively few Covid deaths despite high infection rates.

Obesity certainly increases the individual’s risk of dying from Covid-19 but it is not a decisive factor when comparing nations, as the cases of New Zealand and Australia (both of which have a higher rate of obesity than the UK) can confirm.

Christopher Snowdon
Head of lifestyle economics, Institute of Economic Affairs

Naturally, the letter printed below mine calls for a 50 per cent tax on 'burgers, ketchup, ready meals (unless the individual has a genuine physical or medical reason for exemption) biscuits, cakes, fruit yogurts, gentlemen’s relish, etc.'

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