As obesity rates are set to soar globally, half of children and young people in Australia are forecast to be overweight or obese by 2050. That's according to a major international study, led by Australian researchers, which found children and adolescents in Australia have experienced some of the fastest transitions to obesity in the world. Without urgent policy reform and action, forecasting suggests one third or 2.2 million children and young people in Australia will be obese within the next 25 years, and 1.6 million will be overweight. Lead author Jessica Kerr said substantial increases in obesity expected within the next five years underscored the need for urgent action. "With this level of obesity, it's really important to realise it's the overarching systems and not the children or parents that need to change," Dr Kerr, from the Murdoch Children's Research Institute, said. Despite increased recognition of the risks posed by overweight and obesity, global rates of obesity among children and young people (aged 5–24 years) have tripled over the past three decades, the study found. It is one of two papers published today in The Lancet — the second looking at the global adult population — which together make up the most comprehensive analysis of overweight and obesity rates around the world to date. Together, using data from 204 countries and territories, the studies forecast 60 per cent of adults (3.8 billion) and a third of all children and young people (746 million) will be overweight or obese by 2050, assuming historical trends continue. "The unprecedented global epidemic of overweight and obesity is a profound tragedy and a monumental societal failure," Emmanuela Gakidou, professor of health metrics at the University of Washington and lead author of the adult population study, said. A global problem While almost half the global adult population was estimated to be overweight or obese in 2021, weight gain varies widely around the world. High levels of overweight and obesity among adults and children have already been reached in many parts of Oceania, including Cook Islands, Nauru and Tonga, while among high-income countries, Chile, the United States and New Zealand are most affected. Dr Kerr said there were still many countries, including in south and central Asia and across Europe, that remain "overweight predominant", meaning they have higher rates of people who are overweight than obese. "They still have a chance to beat this obesity crisis [with prevention strategies]," she said. To track global trends, the researchers used body mass index (BMI) measurements for adults and International Obesity Task Force criteria for individuals younger than 18. Recently, international experts have recommended alternative diagnostic criteria for measuring clinical obesity, however according to the researchers, BMI is still considered "the most feasible option" for large-scale monitoring of obesity at a population level. The study found the transition to obesity would be particularly rapid among children and adolescents in North Africa and the Middle East, where the rise coincided with growing populations. "Places we think are struggling with under-nutrition now have increasing prevalence of both overweight and obesity … and the trends are showing this is going to increase," Dr Kerr said. Governments in these countries needed to shift their focus to this "double burden of malnutrition", she said. "They rightly need to keep focusing on under-nutrition and stunting, but at the same time, pay a lot of attention to overweight and obesity as well." Long-term impact of childhood obesity In addition to health system and economic impacts, obesity in childhood and adolescence can have negative consequences on young people's school and community engagement, as well as their mental and physical health, Dr Kerr said. "It's important to bear in mind [obesity] can cause early signs of disease as early as childhood. Things such as fatty liver disease, type 2 diabetes, hypertension, and also fertility problems." Globally, Dr Kerr said adolescent girls entering their reproductive years should be considered a priority population to avoid the intergenerational transmission of obesity and chronic conditions. "We need to support these girls, especially as they enter their reproductive years, because we know that those with obesity who become pregnant are more likely to have children who also struggle with obesity." Tackling obese-promoting environments Jane Martin, executive manager of Food for Health Alliance at Cancer Council Victoria, said the findings were "very concerning" and demonstrated why governments needed to urgently invest in strategies to reduce the population-level drivers of obesity, especially among children. "We have an opportunity to put in place some of those prevention strategies that have been recommended for decades now … such as levies on sugary drinks, and removing unhealthy food marketing," said Ms Martin, who was not involved in the Lancet studies. "It's recognised that there are very powerful industries … and that doesn't just include the processed food industry, it includes all the associated beneficiaries — major sporting codes, media platforms — who have been very effective in lobbying against meaningful change. "At the moment, those vested interests are creating huge profits from selling ultra-processed food packed with cheap ingredients … at the expense of our children's and young people's health now and into the future." Dr Kerr agreed that addressing the commercial determinants of health was essential to turning the tide on rising rates of obesity, in addition to strategies that improve children's nutrition, physical activity and living environments. "It's important to think of it as a health in all policies approach … so looking at things such as urban planning, making sure our neighbourhoods are walkable, and funding school meals in areas that need them. Things that cut across different areas of government." The increasing prevalence of overweight and obesity in Australia was "a biological response" to obesity-promoting environments, she said. "That means these individual-level strategies, while they make so much sense — eat less, move more, get better sleep — they're so difficult for any individual to carry on with for a long period of time when they're living in an environment that is telling them basically to do the opposite thing."