Researchers say the findings of the study challenge the idea of a single global obesity “epidemic”, revealing major differences between countries, age groups and sexes.
Obesity rates have continued to climb sharply in many low- and middle-income countries over the past four decades, while levels have stabilised in much of Western Europe and other high-income nations, according to a major new global study.
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The research, published in Nature, analysed data from 232 million people across 200 countries and territories between 1980 and 2024.
Researchers say the study challenges the idea of describing obesity as a single "global epidemic", which can overlook "the fact that trajectories differ substantially between countries, age groups and sex".
The study was carried out by the NCD Risk Factor Collaboration, a network of nearly 2,000 scientists worldwide, using data from more than 4,000 population-based studies measuring height and weight in people aged five and older.
What is the definition of obesity?
The definition of obesity used by this study - and by most global surveillance - remains the World Health Organization's BMI based framework.
For adults, a BMI of 30 or above is classified as obesity. A BMI between 25 and 29.9 is considered overweight.
For children and teenagers aged 5 to 19, the definition is slightly different. Obesity is measured as having a BMI that is more than two standard deviations above the WHO growth standard for their age and sex.
Findings of the study
According to researchers, in most high-income western countries - including those in Western Europe, North America and Australasia - the rise in childhood obesity began to slow during the 1990s and had largely plateaued by the mid-2000s. In some countries, rates may even be gently declining.
Denmark was among the earliest to see the slowdown, with rates stabilising around 1990. By the 2010s, countries like France, Italy and Portugal were showing signs of a small but meaningful reversal in child obesity - the first time such a types of declines had been observed at a national level.
For adults, a similar trend followed typically about a decade later than for children.
In Western Europe more broadly, adult obesity prevalence in 2024 generally remains below 25 percent, and as low as 11 percent in France - a significant contrast to English-speaking high-income countries.
In the United Kingdom, Canada and the United States, adult obesity rates range from 25 percent to 43 percent.
The alarming picture in the developing world
While many wealthier nations appear to have reached a plateau, the situation is very different in large parts of the developing world.
In most low- and middle-income countries across sub-Saharan Africa, South and Southeast Asia, Latin America and Pacific Island nations, obesity continues to climb - and in many places, the pace of increase is actually speeding up.
In 2024, obesity prevalence was rising fastst of all - at more than half a percentage point per year - in 36 countries for girls and 35 countries for boys. The highest velocities were recorded in Tonga and Samoa for girls, and Peru for boys.
Pacific Island nations present some of the most extreme cases. In Tonga and the Cook Islands, more than 65 percent of the adult population is now obese.
Alarmingly, even in countries where obesity was previously very rare, such as Ethiopia, Rwanda and Bangladesh, rates are now climbing.
What is behind the trends in different countries and what can be done?
The study says there is no single explanation for the global differences.
Instead, obesity trends are shaped by a combination of factors, including access to ultra-processed foods, changes in physical activity, income levels, and how health systems respond.
Public policy also appears to play a role. The authors point to measures such as sugar taxes as one of the few interventions that has shown measurable, if modest, effects on obesity levels at population scale.
However, researches stress that responses to obesity need to be specifically tailored to individual countries: "What is needed is nuanced nutritional and health policies and programmes that are relevant for each country, especially those that support people with lower income and education towards eating healthy foods, having an active lifestyle and using relevant health care interventions to attain and maintain health, functional capacity and quality of life across the life course."
The study also notes that weight-loss medications could become an important tool in future obesity management, but warns that "their highly variable costs through public and private providers are currently an obstacle to increasing their coverage and may increase inequalities."
Overall the study cautions that without stronger and more targeted action, many low- and middle-income countries risk locking in high obesity levels for decades, and placing long-term pressure on health systems.
