The number of obese children and teenagers around the world has risen tenfold over the last four decades, a major new study has found.

According to the findings, if current trends continue, more young people will be obese by 2022 than are underweight.

In the biggest study of its kind ever undertaken, researchers from Imperial College London and the World Health Organization (WHO) analysed the weight and height measurements of almost 130 million people, including over 31 million people aged between five and 19 years.

They found that obesity rates among this age group have jumped significantly over the last four decades. In 1975, less than 1% of young people aged five to 19 were obese, equivalent to around five million girls and six million boys.

However by 2016, 6% of girls in this age group (50 million) and almost 8% of boys (74 million) were obese.

Combined, the number of obese five to 19 year olds jumped tenfold globally, from 11 million in 1975 to 124 million in 2016. A further 213 million children and teenagers were overweight, but fell below the threshold for obesity.

According to the study's lead author, Prof Majid Ezzati of Imperial College London, obesity rates are continuing to soar in low- and middle-income countries, and while they have recently plateaued in higher income countries, they still remain ‘unacceptably high' there.

"These worrying trends reflect the impact of food marketing and policies across the globe, with healthy nutritious foods too expensive for poor families and communities. The trend predicts a generation of children and adolescents growing up obese and also malnourished.

"We need ways to make healthy, nutritious food more available at home and school, especially in poor families and communities, and regulations and taxes to protect children from unhealthy foods," Prof Ezzati said.

The study emphasised that the high number of moderately or severely underweight children and teenagers in the world still represents a major public health challenge, particularly in the poorest regions of the world. In 2016, 75 million girls and 117 million boys were underweight.

However, if current trends continue, there will be more obese children and teenagers than underweight ones by 2022. The study noted that in many middle-income countries, including in East Asia, Latin America and the Caribbean, young people have rapidly transitioned from being mostly underweight to being mostly overweight

The researchers believe this could reflect an increase in the consumption of energy-dense foods, especially highly processed carbohydrates, which lead to weight gain and poor lifelong health outcomes.

"These data highlight, remind and reinforce that overweight and obesity is a global health crisis today, and threatens to worsen in coming years unless we start taking drastic action," commented Dr Fiona Bull of the WHO.

The study found that over the last four decades, the biggest increase in the number of obese children and teenagers was seen in East Asia, the Middle East, North Africa and the high-income English-speaking region, which includes Ireland, the UK, the US, Canada and Australia.

In Europe, girls in Malta and boys in Greece had the highest obesity rates, at 11.3% and 16.7% of the population respectively. Meanwhile, girls and boys in Moldova had the lowest rates, at 3.2% and 5% of the population respectively.

Among all high-income countries, the US had the highest obesity rates for girls and boys.

When it came to underweight children, India was found to have the highest prevalence of moderately and severely underweight children and teenagers. Last year, 22.7% of girls and 30.7% of boys were underweight. Some 97 million of the world's moderately or severely underweight children and teenagers lived in India in 2016.

"The WHO encourages countries to implement efforts to address the environments that today are increasing our children's chance of obesity. Countries should aim particularly to reduce consumption of cheap, ultra-processed, calorie dense, nutrient-poor foods.

"They should also reduce the time children spend on screen-based and sedentary leisure activities by promoting greater participation in physical activity through active recreation and sports," Dr Bull said.

Details of these findings, which were launched to coincide with World Obesity Day (October 11), are published in the medical journal, The Lancet.