Nearly one-third of the world's population is obese or overweight, and an increasing number of people are dying of related health problems, according to the results of a study published Monday.

Some four million people died of cardiovascular disease, diabetes, cancer and other ailments linked to excess weight in 2015, bringing death rates related to being overweight up 28 per cent on 1990, according to the research.

"People who shrug off weight gain do so at their own risk," said Christopher Murray, one of the authors of the study, published in the New England Journal of Medicine.

In 2015, excess weight affected 2.2 billion people — equal to 30 per cent of the world's population, according to the study.

Almost 108 million children and more than 600 million adults weighed in as obese, having a body mass index (BMI) above 30, said the research. Together, that's about 10 per cent of the world's population.

BMI is calculated by dividing a person's weight in kilograms by their height in metres squared, and is an indication of whether a person is a healthy weight. A BMI score over 25 is overweight, over 30 is obese and over 40 is morbidly obese.

According to the World Health Organization, obesity has more than doubled since 1980, reaching epidemic proportions.

Increases among kids

Obesity rates among children were increasing faster than among adults in many countries, including Algeria, Turkey, and Jordan, the study said. And obesity rates have tripled in youth and young adults in countries like China, Brazil and Indonesia.

boy poses with a chicken burger at a fast food outlet in Taipei in this 2010 file photo

Obesity rates have tripled in youth and young adults in countries like China, Brazil and Indonesia, which could mean future increases in diabetes and other global health problems. (Nicky Loh/Reuters)

Those numbers are particularly troubling because it means more young people are on track to become obese adults and develop problems like diabetes, heart disease and a range of cancers, some experts said.

The researchers reported on 195 countries, although data was incomplete or non-existent for many of them. They made assumptions and used mathematical modelling to fill in gaps.

Despite the limitations, "this is the best picture that's out there for global obesity," said Edward Gregg, a diabetes expert at the U.S. Centers for Disease Control and Prevention. He wrote an editorial that accompanied the study.

Some of the study's other findings:

  • Obesity rates doubled in 73 countries between 1980 and 2015. Countries where obesity did not increase significantly included Afghanistan, Bulgaria and the Democratic Republic of the Congo.
  • Worldwide, about five per cent of children and 12 per cent of adults were obese in 2015.
  • Among the 20 largest countries, the United States had the highest level of obesity among children and young adults. Bangladesh had the lowest.
  • Egypt had the highest rate of obese adults. Vietnam had the lowest.
  • But the United States had the largest number of obese adults in 2015, with 79 million. China came in second with 57 million obese adults — even though China has more than four times as many people as the U.S.
  • China had the largest number of obese children, with 15 million. India had 14 million.

'No single simple solution'

Meanwhile, almost 800 million people, including 300 million children, go to bed hungry each night, according to the United Nations.

Poor diets and sedentary lifestyles were mainly to blame for increasing numbers of overweight people, experts said.

Urbanization and economic development have led to increasing obesity rates in poor countries where part of the population doesn't have enough to eat, as people ditch traditional, vegetable-rich diets for processed foods.

With obesity levels rising, there is a pressing need for better nutrition and other efforts to prevent unhealthy weight gain, said Dr. Ashkan Afshin, the study's lead author.

Unfortunately, "there is no single simple solution for the problem of overweight and obesity," he said.

Research in Mexico, Brazil, China, South Korea and Britain by London-based Overseas Development Institute has shown that the cost of processed foods like ice cream, hamburgers, chips and chocolate has fallen since 1990, while the cost of fresh fruit and vegetables has gone up.

With files from Associated Press