Nearly a third of the world's population is now overweight, a new study suggests

Nearly a third of the world's population is obese or overweight and an increasing number of people are dying of related health problems in a "disturbing global public health crisis", a study has said.

Some 4 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 percent 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 percent 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 that covered 195 countries.

More than 60 percent of fatalities occurred among this group, the study by the Institute for Health Metrics and Evaluation (IHME) at the University of Washington found.

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 Organisation, obesity has more than doubled since 1980, reaching epidemic proportions.

Obesity rates among children were increasing faster than among adults in many countries, including Algeria, Turkey, and Jordan, the study said.

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.

Urbanisation and economic development have led to increasing obesity rates also in poor countries where part of the population doesn't 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 Boitshepo Bibi Giyose, senior nutrition officer at the U.N. Food and Agriculture Organization.