Image copyright AFP

Mexicans consume more carbonated drinks per person than any other nation, and the country has one of the world's highest rates of childhood obesity. Two years ago the government introduced a tax on sugary drinks - but is it working?

Silvia Segura lives in a poor neighbourhood on the outskirts of Merida, in Mexico's Yucatan state. She invites us into her modest house. Three armchairs face a television and a ghetto-blaster turned up high with Mexican music blaring out.

On the walls are hooks with hammocks hanging from them. These are where the family sleeps - they are more comfortable than beds in the region's baking climate.

In the living room, however, a double bed stands in the middle of the floor. Silvia says this was her mother's bed after she became too ill to climb into a hammock. She died recently because of complications caused by type 2 diabetes - but until the end, Silvia says, her appetite for sugary drinks never left her.

"All my family drinks Coca-Cola," says Silvia. "My mother, may she rest in peace, was a true cocacolera - she couldn't live without it, she'd drink it three times a day if she could. She said it kept her alive."

When her mother went into hospital, "we'd smuggle the coke in and give her some sips," Silvia says.

About 10% of kids are being fed soda from zero to six months of age Dr Salvador Villalpando, Childhood obesity specialist

Mexicans are the thirstiest consumers of sugary drinks in the world. Each gets through an estimated 163 litres (36 imperial gallons) on average per person every year - 40% more than an average American (who drinks 118 litres, or 26 gallons).

And this, says the government and the health campaigners, is a serious problem.

All too often, the headlines coming from Mexico focus on the country's bloody drugs war - which has claimed over 100,000 lives in the past decade. Type 2 diabetes, on the other hand, kills 70,000 per year.

So acute is the problem that two years ago, in January 2014, Mexico introduced a national tax on sugary drinks and junk food - a 10% tax on every litre of sugar-sweetened drinks and an 8% tax on high-calorie food.

The effect of these on children is a particular concern - according to Mexico's Health Ministry, the country leads the world in childhood obesity.

"About 10% of kids are being fed soda from zero to six months of age," says Dr Salvador Villalpando, a childhood obesity specialist at the Federico Gomez children's hospital in Mexico City.

"By the time they reach two it's about 80%."

Image copyright Thinkstock Image caption It's common for Mexican cafes and corner shops to be painted red and white

Image copyright Thinkstock

The problem is aggravated by the fact that children are often short, their development sometimes hindered both physically and mentally by a diet high in junk food and low in nutrients.

Although the country's appetite for sugary drinks has sometimes been put down to the lack of clean water in some parts of the country, Villalpando disagrees.

"It's cultural," he says.

"Mexican mums like having chubby kids in their homes as it shows they're feeding them properly. And they are so used to feeding them sodas, they don't stop even when there is clean water."

The children coming to his clinic often show early signs of diabetes - patches of dark skin on their necks and regular spikes in their blood sugar levels. Children with pre-diabetes cannot process sugar in the same way as healthy children and after consuming sugary food or drink their blood sugar rises dramatically.

Image copyright Alamy Image caption Acanthosis Nigricans - dark patches of skin - can be a sign of prediabetes

Young children who are accompanied by their mothers have less chance of getting better than teenagers who come alone, Villalpando says. That's because parents continue overfeeding the young children, while often the older ones are determined to lose weight and improve their health.

According to research by Mexico's National Institute of Public Health, together with the University of North Carolina, in the first year the tax reduced consumption of sugary drinks by an average of 6% over the 12 months, reaching 12% by the month of December.

In the poorest households, monthly purchases of sweet drinks fell by a full 17%.

Find out more

What lies behind the global epidemic in diabetes? Stories from Sri Lanka, Mexico and the US - listen to and download the programmes

The Food Chain will host a live debate about diabetes on 5 February - tweet your questions to @BBCWorldService using the hashtag #BBCdiabetes

The drinks industry disputes these figures, however.

"We did an analysis with the National Institute of Statistics and Geography and what we have, until June 2015, is that consumption and sales have been affected by 1% or 2%," says Jorge Terrazas of Mexico's bottled drinks industry body, Anprac.

He adds that fizzy drinks only account for 5.6% of Mexico's average calorie consumption so can only be a small part of the solution to obesity and diabetes.

Image copyright AFP

No data has yet been published that would indicate whether the tax is having an effect on Mexicans' health. But Dr Miguel Messmacher, under-secretary of revenues at Mexico's Ministry of Finance, says he is in no doubt that it is working.

"We've raised close to 20bn pesos (£760m)," he says. "It's a fairly significant amount. I think the results we have so far have led to the changes in behaviour we wanted."

When broccoli tastes like a cheeseburger, I'll eat more broccoli - you don't lecture to people to get them to change Hank Cardello, Obesity Solutions Initiative

So what do the big US brands make of Mexico's approach?

Hank Cardello of the Obesity Solutions Initiative, a research group in Washington DC, cracks open a can of diet ginger ale and tells us.

"You have to look at ways of expanding the tool kit of solutions," he says.

"The typical regulatory tool kit is tax, ban, limit, constrain - those kinds of anti-growth words, if you would. They're anathema to what the companies have to do.

"We should ban the word 'should'. It's like a parent talking to a child. 'You should eat better, you should do this.'

"No. When broccoli tastes like a cheeseburger, I'll eat more broccoli. You don't lecture to people to get them to change."

Image copyright iStock

But in Berkeley, a short drive from San Francisco, Josh Daniels sees things very differently.

He was the co-chair of the "Yes on Measure D" campaign, which resulted in an overwhelming vote in favour of introducing a soda tax in November 2014 - the first in the US.

The tax is one cent per ounce, which amounts to about 10% of the value of a bottle of soda, just as in Mexico. It raises about $150,000 per month for health-focused community initiatives.

"I came to understand the damage that sugary drinks have been doing," says Josh. "By showing that Mexico did it and was successful, it gave support to our position that this was a viable policy."

Now the city is leading the way for other US cities, he says, 31 of which have already tried and failed to introduce a tax, but may try again.

The idea of a sugar tax has also been floated in the UK.

In October a report by Public Health England recommended a tax of between 10% and 20% on high-sugar products as one measure needed to achieve a "meaningful" reduction in sugar consumption. Food Standards Scotland also proposed a sugar tax two weeks ago.

"I don't really want to put new taxes on to anything but we do have to recognise that we face potentially in Britain something of an obesity crisis," Prime Minister David Cameron said last month, promising to announced details of a "fully worked-up programme" to tackle obesity later in the year.

In Mexico, the tax may be working but sometimes it can be hard to see how.

Across the country, corner shops are painted red and white, reminding Mexicans where their loyalties lie.

Posters tempt school children with cheap offers of fizzy drinks and sugary snacks on their way to school. It makes you wonder whether Mexico's thirst for pop can ever be truly quenched.

Do you think sugar companies should pay a "sin tax"? What role should government play? The BBC World Service is holding a live debate on Friday 5 February at 13:00 GMT. Send your questions to thefoodchain@bbc.co.uk or via Twitter to @bbcworldservice using the hashtag #bbcdiabetes

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