Transcript

This week, commuters in London will see a difference in the kinds of advertisements in the city's subways, buses and bus shelters and taxi cabs.

Posters for food and drink high in sugar, fat and salt are being stripped from property owned by Transport for London, the governing body for transit.



On Monday, London's mayor Sadiq Khan said the ban will help tackle childhood obesity in London.

Public health professor Linda Bauld, a prevention expert at Cancer Research UK, which supported the ban, spoke with As it Happens host Carol Off. Here is some of their conversation.

How big is the problem with childhood obesity in London?

It's very substantial. London has some of the highest rates of obesity in the U.K. — around four in 10 children between the ages of 10 and 11 are obese.

And in England overall, what's frightening is that around one in five children start school overweight or obese, and that goes up to one in three when they move on to secondary school.

So unfortunately, like Canada ... it is a public health crisis here.

A general view of Piccadilly Circus in London, U.K. (Alessia Pierdomenico/Reuters)



And what evidence is there that if you take the advertising for fast food off of bus shelters and tube carriages, it will have any effect?



I think as a single measure, it's probably limited. I think as a single measure, it's probably limited.

But we do know the effect of junk food marketing generally on children's consumption, so it affects the choices they make, or the foods they ask their parents to buy.

And kids who are exposed to junk food marketing in the outdoor environment, on TV or streaming services are far more likely to eat those foods. And that exposure is dose-dependent.

So if they're seeing more adverts ... they're more likely to consume those foods.

It's affected what kids and their parents see as normal. - Linda Bauld , prevention expert at Cancer Research UK

But how many of the bad food choices that young people make are actually choices, and not the lack of access to other kinds of food?

It's no doubt that poverty is an issue. But unfortunately in the U.K., we have what we call an obesogenic environment.

In the last 30 years, for example, rates of childhood obesity have almost tripled here — very similar to Canada. And that's because the foods that are available and that people are consuming are cheap, and they have a limited nutritional content, and they're heavily-marketed.

Our fast food industry, for example, has grown substantially. And marketing is only one part of the picture, but it definitely has some effects.



But a kid who's not getting fed properly at home and wants to feel just a bit of fullness in the belly — they're going to go to what they can find, which is fast food, right?



Yeah, and a lot of those places are available near schools, absolutely. And we don't want anybody to go hungry. It's not about that.

But the problem is that the junk food marketing and the pricing [of] those products has pushed out some of the healthier products.

And also, from my perspective, it's affected what kids and their parents see as normal. So if all your friends and family are consuming those foods — they're getting a lot of their calories from those energy-dense foods — then it makes it acceptable, it makes it part of what people routinely do.

And that's why our diet has changed over the last few decades. So it's really something we need to shift. And that's why the mayor of London has taken just one step — but it's an important step — this week.

London Mayor Sadiq Khan travelling with passengers on a northbound Victoria line tube train in 2016. (Yui Mok/PA Wire/Reuters)

The fast food companies will still be able to advertise on transport services if they feature salads and other things on their menu of that nature, right?

There's been a lot of concern about the economic impact of removing those adverts. And certainly the mayor of London has said that many of the companies, you know, they produce a range of products — they're still buying advertising space, they're just being forced to advertise the healthier products.

Where will you see the results? Because you mentioned there's got to be more than just removing the advertising, the food eating. The choices have to change. So how will you measure whether this is successful?

In the U.K., we have a childhood obesity strategy, which we're hoping will be implemented. And that talks about banning junk food marketing from television, for example, for children. It talks about increasing the price of the most unhealthy products, and also reducing some of the promotions in the retail environment.

You know, I'm looking for small changes.

These things don't happen quickly. But through small, cumulative steps, we hope to see that evidence in the future.

Interview produced by Ashley Mak. Q&A edited for length and clarity.