The Overseas Development Institute hit the headlines today with a shocking statistic: one in three adults across the world is overweight or obese.

And it’s not just rich countries that are getting fatter. The majority of overweight people can now be found in the developing world.

Why is the world’s waistline expanding and is there anything we can do about it?

What have we found out today?

Actually the statistics on global obesity came out last year and are based on 2008 data from local studies and surveys of populations around the world.

The researchers used Body Mass Index – weight divided by height – to categorise people as under or overweight or obese (very overweight, with a score of 30 or more).

BMI has its critics. If you are bigger or, like FactCheck, have impressive amounts of lean muscle mass, you tend to be unfairly classed as overweight.

But to get a more accurate test you would have to start measuring people’s waists or pinching their wobbly bits with calipers, so when dealing with whole populations we are probably stuck with BMI for now.

The latest evidence suggests that 34 per cent of the population of the world is overweight or obese, up from 24 per cent in 1980.

That’s 1.46 billion people. Half of them live in China, the US, India, Russia, Brazil, Mexico, Germany, Indonesia, and Turkey.

More than half of men were overweight in 100 countries in 2008, and middle income countries are catching up fast with the developed countries.

The regions with the highest prevalence of obesity were North Africa and the Middle East, Central and Southern Latin America, Southern Sub-Saharan Africa and high-income North America, with 27.4 to 31.1 per cent of the population classed as obese.

Between 1980 and 2008, the number of obese or overweight people in the developing world more than tripled, going from 250 million to 904 million. In high-income countries the number went up 1.7 times.

The authors illustrate the changing trends with these world maps. This is 1980. The redder, the fatter.

And here we are in 2008, with excess weight in parts of Central and South America, North Africa and the Near East matching levels in the richest parts of the world. The data is for men only, but the pattern is almost identical for women.

Almost everyone is getting more calories, and eating more fat, sugar and animal protein in particular.

Most doctors agree that obesity, along with the excessive consumption of fat, sugar and salt, carry a range of health risks including heart disease, diabetes and some cancers.

Is it all bad news?

That depends on how you look at it. The ODI paper points out that food has got considerably cheaper in recent decades. Wheat and maize cost about a quarter of what they did in real terms in 1957. And incomes have generally risen in the developing and developed world.

That doesn’t mean no one goes hungry any more. The total number of people defined as undernourished (getting less energy than they need) by the UN Food and Agriculture Organization (FAO) has gone up in Africa and the Near East in the last 20 years.

But it does explain why the number of undernourished people across the world has fallen. The FAO says 842m people were hungry in 2011-13, compared to 1bn in 1990-92.

Although England undeniably has an obesity problem, there are some chinks of light. Last year, the proportion of children in the final year of primary school who were obese or overweight fell for the first time in six years, according to the Health & Social Care Information Centre.

This followed statistics from the Health Survey for England which show that the prevalence of overweight and obese children aged 2 to 15 has fallen slightly after a peak in 2004.

Obesity rates among adults rise sharply in the 1990s and early 2000s but have also remained stable since 2005.

Are we all eating the same things now?

In general, people are eating more meat, fat and sugar.

But that doesn’t mean the whole world is gradually adopting the same homogenous diet.

Actually, different cultures can be surprisingly resilient to the forces of advertising and globalisation.

Zooming in on the average diet in China, Egypt, India, Peru and Thailand, the ODI found that while everyone is eating more, there is still a lot of diversity between what people eat, with some countries eating much more fruit and veg too.

While meat consumption tends to rise with income, there are many countries that buck the trend. India has seen little increase in meat-eating, despite increasing wealth, suggesting that cultural and religious traditions can have a strong influence on what people eat.

What can we do about obesity?

The big question. The thrust of the ODI’s research is governments can and should intervene to try to encourage people to eat better.

We’ve FactChecked the idea of a levy on sugary soft drinks and found a lack of hard evidence on whether such a “fat tax” would work or not. This report doesn’t add much to that debate, but the ODI comes up with some interesting case studies of other kinds of state intervention.

In South Korea people eat very little fat and large and increasing amounts of fruit and veg – a trend attributed to public campaigns to preserve healthy elements of the country’s traditional diet.

In 2004, Denmark placed restrictions on the amount of industrially produced trans-fatty acids allowed in food, forcing fast food chains like McDonald’s and Kentucky Fried Chicken to drastically reduce the ingredient and apparently cutting rates of heart disease.

On the other hand, the Norwegian government tried to change the national diet by using subsidies to promote skimmed milk and fish over sugar and beef.

People’s eating habits did change, but levels of fat consumption and obesity still went up.

The ODI concludes by pointing out that while governments have so far been reluctant to start banning and taxing unhealthy food, “it is only a matter of time before a turning point arrives at which there is more appetite for stronger and effective measures to influence diets”.

By Patrick Worrall