A new study has revealed that one-fifth of adults worldwide will be obese by 2025. Getty Images

A new study has revealed that by 2025, one-fifth of adults worldwide and a third of those in the UK will be obese. The Lancet journal research has warned that if the present trends continue – with the average body mass index (BMI) increasing for both men and women – obesity will become a global health issue.

"Over the past 40 years, we have changed from a world in which underweight prevalence was more than double that of obesity, to one in which more people are obese than underweight," said the study's senior author Majid Ezzati from the school of public health at London's Imperial College London. "If present trends continue, not only will the world not meet the obesity target of halting the rise in the prevalence of obesity at its 2010 level by 2025, but more women will be severely obese than underweight by 2025."

The research studied data covering a population of nearly 19.2m men and women aged 18 and over from 186 countries between 1975 and 2014. Researchers found that the last 40 years saw a rising trend in obesity worldwide – from 105m people in 1975 to 641m in 2014 - and concluded that the world now has more overweight than underweight people.

Amongst other findings, included a shocking conclusion that the UK will have the highest obesity rate amongst both men and women in Europe by 2025, it was also revealed that the English-speaking countries are the worst-hit, with one-fifth of the world's obese adults found living in six high-income English-speaking countries – Australia, Canada, Ireland, New Zealand, the UK and the US.

The research also analyzed underweight people and found that the proportion of underweight people fell by nearly one third in both men and women. Despite the positive news, over one fifth of men in India, Bangladesh, Timor-Leste, Afghanistan, Eritrea and Ethiopia and a quarter or more of women in Bangladesh and India still remain underweight, said the researchers.