The model, based on the most recent Australian data by Sydney researchers, is part of a wider project examining the most effective ways to combat obesity.
It suggests that around two-thirds of adults currently have a body mass index greater than 25, which is considered overweight—and the situation is set to become significantly worse over a short period of time.
The data predicts that obesity among adults will reach 35% by 2025, up from its current level of 28%.
Even more concerning is the prevalence of severe obesity: by 2025, 13%—or one in eight Australian adults—will have a BMI of over 35. This figure is up from just 5% in 1995 and 9% in 2014/15.
Women will fare worse, with one in six predicted to be severely obese compared to one in 10 men.
The model is the first to predict weight gain among all Australian adults and reflect changes in the proportion of overweight, obese and severely obese people over time, according to lead researcher Alison Hayes of Sydney University’s School of Public Health.
She said that middle age is not the time when people suddenly pile on the pounds, contrary to widespread belief, but it is when people are still young.
“In fact, at a population level, young people gain more weight each year than older people. But for most of us weight gain tends to be cumulative and so we’re more likely to move into an overweight or obese category later in life,” Associate Professor Hayes said.
“An increase in childhood obesity means Australians are starting out adulthood with a higher BMI and higher levels of obesity than ever before.”
Indeed, in 1995 around one in 10 young adults were obese, but by 2014 that figure had nearly doubled.
The model takes this, and the fact that most sectors of the population gain weight throughout their increasingly longer lives, into account by calculating the amount of weight that adults put on every year depending on age, sex and current weight, as well as the BMI of adolescents as they enter adulthood.
It also takes into account the national birth rate, current life expectancy in Australia and higher mortality of people with high BMI.
The World Health Organisation target to maintain 2010 levels of overweight and obese people will not be met in Australia, the modelling shows.
“We compared model predictions of obesity and severe obesity starting in 1995 all the way to 2014, and they were consistent with what actually happened,” Dr Hayes said.
“This means we can be very confident about the predictions into the future.”
The model can be used to guide intervention policy by allowing researchers to pose different scenarios, such as finding out what happens if weight gain in young adults is reduced by 10%, or if childhood obesity is reduced.
These scenarios would each have an impact on the projections, and can be used to help establish where policymakers’ efforts should be priorities, Dr Hayes added.
The team will now examine evidence for successful prevention or weightloss programmes and use the model to help work out the most effective—and cost-effective—ways to manage obesity in the future.