Has Sadiq Khan’s junk food ad ban really stopped London getting fatter?

London Mayor Sadiq Khan made a bold claim this week: ‘As a result of our junk food advertising ban on Transport for London, nearly 100,000 cases of obesity have been prevented since 2019.’ Hailing the ‘incredible result’, Khan said ‘it’s expected to save the NHS over £200 million’. Is it true though?

To ascertain whether the ban worked, researchers from Sheffield university and the London School of Hygiene and Tropical Medicine produced a graph. They found that there were some 4.8 per cent fewer obese people than expected and 1.8 per cent fewer overweight people.

What they didn’t do was actually count the obesity rate in London’s population. Instead, their estimates were based on a mathematical model. And as Christopher Snowdon has pointed out the modelling is questionable. The model concludes that after the ban came into effect, Londoners purchased 1,000 fewer calories of high fat and sugary foods. Rather than comparing frequent tube travellers to Londoners who don’t use the underground, it relied on people in the North East as a control group.