It's very easy to become overweight or obese in Australia. Current figures show more of us are than not, with around two thirds of adults having a body mass index greater than 25.
And the situation is set to become significantly worse.
Researchers at the University of Sydney, the Charles Perkins Centre and the George Institute for Global Health have developed a model based on the most recent Australian data.
They predict obesity among adults will reach 35 percent by 2025, up from its current 28 per cent level. Even more concerning is the prevalence of severe obesity; by 2025, 13 percent or one in eight adults will have a BMI of over 35 – up from just five percent in 1995 and nine percent in 2014/15.
Women will fare worse, with one in six predicted to be severely obese compared to one in 10 men.
Lead researcher, Associate Professor Alison Hayes from the University's School of Public Health, says the model is the first to predict weight gain among all Australian adults and to reflect changes in the proportion of overweight, obese and severely obese people over time.
"Contrary to popular belief, it's not in middle age that people suddenly pile on the pounds," she explains. "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".
Professor Hayes says an increase in childhood obesity means Australians are starting out adulthood with a higher BMI and higher levels of obesity than ever before. For example, in 1995 around one in 10 young adults were obese, but in 2014 it was closer to one in five. We're also living longer, and most sectors of the population gain weight throughout their life.
"The model takes all this into account by calculating the amount of weight that adults put on every year depending on their age, sex and current weight, as well as the BMI of adolescents as they enter adulthood," she says. "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's targets 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," Professor Hayes says. "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 "What happens if weight gain in young adults is reduced by 10 per cent?" or "What if we reduce childhood obesity?" — and see the impact on projections.
"We know an increase in obesity and severe obesity will result in higher rates of chronic disease such as type 2 diabetes, cardiovascular disease and cancer, with an increased strain on the health system and healthcare costs," Professor Hayes says.
"Any reduction in the incidence of obesity going forward will have beneficial impacts on population health and the healthcare costs, but the model can help establish where our efforts should be prioritised".
Just this week the CSIRO released stunning new information about the average Australian diet, revealing we are eating far too much junk food, and not enough of the good stuff.
Professor Hayes says the next phase of her research will examine the evidence for successful prevention or weight loss programs, and use the model to help work out the most effective — and cost-effective — ways to manage obesity in the future.