A new study provides evidence of a sharp increase in the number of obese and overweight children and young adults worldwide in just 40 years.

The study was a project of researchers at Imperial College London and the World Health Organization (WHO). The findings were released this week at WHO's headquarters in Geneva, Switzerland.

Obesity is a condition in which the body stores large, unhealthy amounts of fat. Obese individuals are considered overweight.

The researchers studied obesity rates among children and young people, between five and 19 years of age. They found that rates in this group increased from 11 million in 1975 to 124 million in 2016.

This was one of the biggest epidemiological studies ever done. The researchers examined height and weight data for about 130 million people. They used this information to get the Body Mass Index measurements of the subjects.

The most striking changes have taken place in Middle Income Countries in areas such as East Asia, the Middle East and North Africa, and Latin America. The WHO defines Middle Income Countries as places where a person normally earns between $1,045 and $12,736 every year.

Majid Ezzati, a professor at Imperial College London, was the chief writer of a report on the study. He was surprised by the speed of change.

"So places that a few decades ago, there may have been very little obesity and a fair amount of underweight [children], suddenly are having bordering epidemics."

In countries where wages are higher, the growth of childhood obesity has slowed, but remains high. The United States had the highest obesity rates for this income group.

Researchers say the world's obesity problem is a result of food marketing and poor policymaking in many areas.

Ezzati notes that, in general, young people are not to blame.

"Rather than sort of being an individual's choice, it's hard environments that people choose their foods in – healthy foods being priced out of reach, and especially out of reach of poor, and unhealthy foods being marketed aggressively, together with perhaps not having a safe playing area for children, that are leading to weight gain."

Being overweight can cause many diseases later in life, including heart disease, stroke, diabetes and some cancers. Ezzati says obesity also has a big effect on children, with some evidence suggesting it can affect their educational performance.

Underweight also a problem

The study also looked at underweight children, which continues to be a major health problem in the world's poorest areas.

Ezzati says the researchers found that India had the highest rates of moderately and severely underweight young people.

"We really need to deal with the two issues at the same time. So we can't wait to deal with underweight, and then worry about overweight and obesity. They are all different forms of malnutrition."

The report warned that if current trends continue, levels of child and adolescent obesity could pass those of moderately and severely underweight children by 2022. It said these problems are especially serious in some parts of Asia and African countries south of the Sahara Desert.

Global solutions

The report is calling for policymakers to find ways to make healthy food more available at home and school, especially in poorer families and communities. It also calls for higher taxes on unhealthy foods.

The WHO's Fiona Bull says effective, low-cost measures to lower childhood obesity are available.

She said solutions include restricting marketing, taxing some food products, and creating better food labeling policies. She said that better labels will give people, "clear information about the contents of food ... like the salt, fat, and sugar content."

Bull added that children should be spend less time playing games on the Internet or watching television, and instead turn to more physical activities and sports. She said obese children are likely to become obese adults. This means they risk early death from obesity-related diseases.

I'm Anna Matteo.

Henry Ridgwell and Lisa Schlein reported on this story for VOANews. Phil Dierking adapted their reports for VOA Learning English. George Grow was the editor.