In what is deemed the "most comprehensive global study to date," researchers have found that over the past 3 decades, there has been a "startling" increase in rates of obesity worldwide, with no significant decline in any country.

A team of international researchers, led by Prof. Emmanuela Gakidou of the Institute for Health Metrics and Evaluation at the University of Washington, recently published their findings in The Lancet.

All over the world, obesity is becoming an increasing concern. The condition can increase the risk of numerous health problems, including high blood pressure, stroke, type 2 diabetes and heart disease.

For their study, the team conducted a comprehensive review of surveys, reports and scientific literature looking at overweight and obesity prevalence among adults aged 20 years or older and children ages 2-19 years between 1980 and 2013. Data was drawn from 188 countries over all 21 regions of the world.

Overweight was defined as a body mass index (BMI) of 25 kg/m2 or higher and obese was defined as a BMI of 30 kg/m2 or higher.

Significantly high adult obesity increases in the US

The researchers found that over the past 33 years, worldwide overweight and obesity rates among adults have increased by 27.5%, while such rates among children and adolescents have increased by 47.1%. Collectively, the number of overweight and obese people worldwide has increased from 857 million in 1980 to 2.1 billion in 2013. Of these, 671 million are obese.

The biggest increases in overweight and obesity rates occurred between 1992 and 2002, primarily among adults ages 20-40.

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The researchers found that over the past 33 years, worldwide overweight and obesity rates among adults have increased by 27.5%.

At present, more than half of the obese worldwide population reside in only 10 countries, including the US, China, Russia, Brazil, Mexico, Egypt, Germany, Pakistan and Indonesia.

The team found that 62% of the world's obese individuals live in developed countries. The US had the highest increases in prevalence of adult obesity - a third of the population are now obese. This is followed by Australia - where 28% of men and 30% of women are obese - and the UK - where around a quarter of the adult population are obese.

Developed countries also saw very high increases in overweight and obesity rates among children. Rates increased from 17% to 24% between 1980 and 2013 among boys, and from 16% to 23% among girls in the same period.

Significantly high rates of overweight and obesity were reached in Tonga, where obesity levels among both men and women are over 50%. More than 50% of women are obese in Kuwait, Libya, Qatar, the Pacific Islands of Kiribati, Federated States of Micronesia and Samoa.

Among men, those living in the US, New Zealand, Bahrain, Kuwait and Saudi Arabia saw the highest increase in obesity levels over the past 3 decades, as did women living in Egypt, Oman, Saudi Arabia, Bahrain and Honduras.

But it is not all bad news. The researchers note that in developed countries, the rate of increase in adult obesity has slowed over the past 8 years. Furthermore, the team says that recent birth cohorts indicate a slower weight gain, compared with previous birth cohorts.

Prof. Gakidou says that unlike other major global health risks, such as smoking, obesity rates are not falling. But he says the statistics do offer some hope:

"Our findings show that increases in the prevalence of obesity have been substantial, widespread, and have arisen over a short time. However, there is some evidence of a plateau in adult obesity rates that provides some hope that the epidemic might have peaked in some developed countries and that populations in other countries might not reach the very high rates of more than 40% reported in some developing countries."

WHO obesity campaign 'ambitious and unlikely to be attained'

Last year, members of the World Health Organization (WHO) launched a campaign to stop increases in obesity by 2025. But the research team says that based on these latest findings, this target is "very ambitious and unlikely to be attained."

The team says that in order to reduce rates of obesity worldwide and reach this target set by WHO, "urgent global leadership" is needed to implement strategies that discourage excessive caloric intake, physical inactivity and promotion of food consumption.

In an editorial linked to the study, Prof. Klim McPherson of Oxford University in the UK agrees. He says:

"An appropriate rebalancing of the primal needs of humans with food availability is essential, which would entail curtailing many aspects of production and marketing for food industries. To prevent unsustainable health consequences, BMI needs to return to what it was 30 years ago."

The researchers note that there are some limitations to their study. For example, they included surveys that collected self-reported weights and heights. Although they corrected such data as best they could, this may have influenced figures.

They also point out that the statistics are based on BMI, but this measure does account for body variations across different ethnic groups.

Earlier this year, Medical News Today reported on a study by researchers from the Centers for Disease Control and Prevention (CDC), which found that obesity rates have fallen by 43% among children ages 2-5 years in the US, but have increased among women aged 60 and over.