ROME • Nearly a third of the world's population is obese or overweight and an increasing number of people are dying of related health problems, creating a "disturbing global public health crisis", according to a new study.

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, the study said.

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

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

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 that covered 195 countries.

More than 60 per cent of fatalities occurred among this group, according to the study by the Institute for Health Metrics and Evaluation at the University of Washington. More than two-thirds of deaths linked to a raised BMI were attributed to cardiovascular diseases, marking a sharp increase since 1990.

"Those half-serious New Year's resolutions to lose weight should become year-round commitments to lose weight and prevent future weight gain," Dr Murray said.

BMI is calculated by dividing a person's weight in kilograms by his 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 Organisation, obesity has more than doubled since 1980, reaching epidemic proportions.

Egypt topped the list for adult obesity at about 35 per cent. Bangladesh and Vietnam had the lowest rate - at 1 per cent. The US with 79.4 million and China with 57.3 million had the highest total numbers of obese adults in 2015.

Obesity rates among children were increasing faster than among adults in many countries.

China with 15.3 million and India with 14.4 million had the highest numbers of obese children.

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

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

"People are consuming more and more processed foods that are high in sugar and fat, and exercising less," said Dr Boitshepo Bibi Giyose, a senior nutrition officer at the UN Food and Agriculture Organisation.

Research in Mexico, Brazil, China, South Korea and Britain by the 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 fruit and vegetables has gone up.

"What people eat is the key factor in whether they become obese or not," said Dr Adam Drewnowsk, director of the Centre for Public Health Nutrition at the University of Washington, who was not affiliated with the study, which he deemed "brilliant work by the best people in the business".

He said getting people healthy food was easier said than done.

"It is all very nice to talk about the need to eat less unhealthy foods and more healthy foods," he said. But "unhealthy foods cost less; healthier foods often cost more. People eat what they can afford".

The report said a worldwide general slowdown in physical activity was probably not a major factor.

REUTERS, AGENCE FRANCE-PRESSE, NYTIMES