Rich countries are facing an epidemic of severe obesity and around one in five worldwide will be obese by the middle of next decade unless there is a major slowdown in the rate at which people are putting on weight, according to a major international study involving data from 19 million adults across 186 countries.

Already, more than 2 per cent of men and 5 per cent of women are severely obese, and researchers have warned that the prevalence is set to increase and current treatments like statins and anti-hypertensive drugs will not be able to fully address the resulting health hazards, leaving bariatric surgery as the last line of defence.

In a result which underlines the extent of the obesity challenge, research by the NCD Risk Factor Collaboration* has found that that between 1975 and 2014, the prevalence of obesity among men more than trebled from 3.2 per cent to 10.8 per cent, while among women it surged from 6.4 to 14.9 per cent.

The study’s authors warned that on current trends, 18 per cent of men and 21 per cent of women will be obese by 2025, meaning there was “virtually zero” chance of reaching the global target of halting the prevalence of obesity at its 2010 level.

Instead, in the next nine years severe obesity will supplant underweight as a bigger public health problem, especially for women.

“The world has transitioned from an era when underweight prevalence was more than double that of obesity, to one in which more people are obese than underweight,” the study, published in The Lancet, said.

But although the world is getting fatter, it is also getting healthier, confounding concerns about the detrimental health effects of being overweight.

Writing in the same edition of The Lancet , British epidemiologist Professor George Davey Smith said that the increased in global body mass index (BMI) identified in the study had coincided with a remorseless rise in average life expectancy from 59 to 71 years.

Professor Davey Smith said this was a paradox, given the “common sense view that large increases in obesity should translate into adverse trends in health”.

Generally, a BMI greater than 25 kilograms per square metre is considered to be overweight, while that above 30 is obese and above 35, severely obese.

As the BMI increases above the “healthy” range, it is associated with a number of health consequences including increased blood pressure, higher blood cholesterol and diabetes.

The fact that increased BMI has not so far been associated with decrease longevity has led Professor Davey Smith to speculate that in wealthier countries access to cholesterol lowering drugs and other medications have dampened the adverse health effects, sustaining improvements in life expectancy despite increasing weight.

But he warned this effect would only be limited – many people would not be able to afford such treatments, and pharmacological interventions can only alleviate some of the health problems associated with being obese, meaning many health effects are likely to emerge in greater number later on as the incidence of obesity increases.

One of the most important aspects of the NCD Risk Factor Collaboration report is the insight it provides into differences in the nature and prevalence of weight problems between countries and regions.

For instance, it shows that the biggest increase in men’s BMI has occurred in high-income English-speaking countries, while for women the largest gain has been in central Latin America.

At the extreme, the greatest prevalence of overweight and obesity was in American Samoa, where the age standardised mean BMI for was 32.2, and for women, 34.8. Other areas where the mean BMI for both men and women exceeded 30 included Polynesia, Micronesia, the Caribbean, and several countries in the Middle East and north Africa, including Kuwait and Egypt.

The researchers found that male and female BMIs were correlated across countries, though women on average had a higher BMI than men in 141 countries.

But, in a sign that the rate of weight gain in a country may slow after a certain point, the researchers found that from 2000 BMI increased more slowly than the preceding 25 years in Oceania and most high income countries.

Alternatively, it sped up in countries where it had been lower. After 2000, the rate of BMI increase steepened in central and eastern Europe, east and southeast Asia, and most countries in Latin America and Caribbean.

The results suggest that public health campaigns and other polices aimed at curbing weight gain and encouraging healthier diets and more physical exercise are so far having little effect, spurring policymakers to consider different measures.

Though not canvassed in the study, one idea gaining support intnationally is for governments to impose a tax on sugary foods.

The United Kingdom will levy a tax on sugary drinks from next year, similar to one already in place in Mexico, and the World Health Organisdaiton has backed the policy as a way to curb the rapid increase in cases of diabetes in the world.

While overweight and obesity has become a major public health problem, particularly in wealthier countries, inadequate nourishment remains a health scourge in much of the world.

The NCD Risk Factor Collaboration report shows that millions continue to suffer serious health problems from being underweight, and warned that “the global focus on the obesity epidemic has largely overshadowed the persistence of underweight in some countries”.

As in other respects, global inequality in terms of weight have increased in the past 40 years, and while much of the world is getting fatter, in many areas under-nutrition remains prevalent.

The study found that more than 20 per cent of men in India, Bangladesh, Timor Leste, Afghanistan, Eritrea, and Ethiopia are underweight, as are a quarter or more of women in Bangladesh and India.

* The study drew on 1698 population-based data sources involving body mass index measurements taken from 9.9 million men and 9.3 million women in 186 countries between 1975 and 2014.

Adrian Rollins