OBESE NATION: It’s time to admit it - Australia is becoming an obese nation. Today we launch a series looking at how this has happened and, more importantly, what we can do to stop the obesity epidemic.
In Australia today, around two-thirds of adults and a quarter of children are overweight or obese. This is a dramatic change from the landscape just 30 years ago when we first collected national data on weight and height.
In 1980, around 60% of Australian adults had a healthy weight; today this has almost halved to around 35%. In 1980, just 10% of adults were obese. In 2012, this figure tips 25%. The infographic below shows just how quickly obesity is increasing in Australia. And why it’s not an exaggeration to call it an epidemic.
The same trend is seen around the world, with around a third of adults and almost one in five children in the United States obese. In some island nations, the prevalence is higher still, with more than half of Samoan and Tongan women classified as obese.
In Australia, we see a higher prevalence of obesity in a number of marginalised populations, such as Aboriginal and Torres Strait Islander adults, Australians living outside the major cities, and those living in more socioeconomically deprived areas.
With excess weight and obesity increasing your likelihood of developing many major chronic diseases, disability and early death, governments and communities around the world are working to halt, or at least slow, this trend.
Some encouraging reports have emerged recently from Australia, the United States and several European countries that show rates of obesity are stabilising in children. But the good news is limited to specific age groups and time periods (and the studies are yet to be replicated to confirm the results). Overall, rates of childhood overweight and obesity remain high.
There are two key objectives in dealing with Australia’s collective weight gain: we must both prevent the ongoing shift towards a heavier population, and increase the proportion of children and adults at a healthy weight. But before we can even contemplate either, we need to understand the drivers of these trends.
Why do we gain weight?
A person’s weight gain is generally caused by an imbalance between energy intake and energy expenditure. This appears simple, but the factors driving this imbalance at a population level are incredibly complex, making simple solutions elusive.
It’s commonly understood that the overweight and obesity we experience today is a normal response to an abnormal environment – often referred to as the obesogenic environment. The premise of this idea is that as humans we’re programmed to conserve energy, storing it up for a time when food is scarce. But most of us now live in an environment where food is plentiful.
On top of this, our need to expend energy in daily life has disappeared. Within our lifetimes we’ve seen the dominant move towards sedentary jobs and leisure-time pursuits, such as watching television, playing computer games and shopping online. We all also recognise the ease and affordability of foods high in energy.
The data supports our anecdotal understanding of these trends. While difficult to measure accurately, a comparison of Australian energy intake from the mid-1980s to the mid-1990s shows an increase in daily energy intake of around 13% for children and 3% to 4% for adults. This latter increase, of around 350kJ a day (approximately half a can of soft drink, or a slice of bread), equates to an eventual weight gain of around 3.5kg.
Similar trends have occurred in the United States, with a 2004 Centres for Disease Control and Prevention (CDC) report indicating daily energy intake between 1970 and 1990 increased by around 7% in men and 22% in women.
Unfortunately, it’s difficult to measure exercise and activity levels over time. A recent report of US workers suggested that while almost half of jobs in the 1960s entailed at least moderate levels of activity, less than 20% do so now.
Trends in overall physical activity levels are more difficult to compare, as different studies generally evaluate different aspects of total physical activity (leisure time, occupational activity, incidental movement, among other measurements). But most Australian and US data suggest recreational activity levels have decreased slightly over past decades.
A recent review by Boyd Swinburn and his colleagues proposes a framework for understanding the combined forces of changes in our energy intake and activity levels. Prior to the 1960s, the dominant change was decreased levels of physical activity, but this had no observable effect on population weight status as food remained a limiting factor. Subsequent to the 1960s, the rapid changes in food availability, composition and marketing drove rapid increases in population weight, now against a backdrop of minimal activity.
The authors also highlight the strong correlation between national economic status and obesity: the move to affordable and accessible high-energy foods requires a certain level of economic wealth and activity. In this sense, the obesity epidemic can be seen as a detrimental outcome of our society’s over-consumption.
Clearly, our food and activity environments require the dominant focus in our efforts to tackle population weight gain. But there are a number of other contributors to weight gain that are also being evaluated for their potential role in achieving healthy population weight.
At an individual level, we know that the in utero environment influences the future child’s weight and chronic disease pathways, with both under- and over-nutrition linked to excess weight gain later in life. We also know that factors such as lack of sleep, low-quality sleep, and use of particular medications, life stages such as pregnancy, and specific genetic variations are also predictive of weight gain. Work to determine the importance of these factors at a population level is ongoing.
There are also newly identified candidates predictive of weight gain, including exposure to environmental toxicants such endocrine disruptors, Bisphenol A (BPA), phthlates and persistent organic pollutants. New studies have also suggested a link between some viral infections, such as human adenovirus, and obesity.
Reversing the trend
Successful population health campaigns to improve the levels of healthy weight, activity and nutrition in our population will need to focus on addressing the overarching drivers of the food and activity environments, while also taking into account these other factors that predict individual variation in weight gain.
The launch last year of the Australian National Preventive Health Agency’s Strategic Plan recognises the importance of this approach. It’s critical that we continue to work towards implementing a range of interventions appropriate for each stage of prevention and treatment, from childhood to adulthood.
Currently, only a third of Australian adults have a healthy weight. If these trends continue, this could decrease to around one quarter over the next decade. There is a real risk that if we are not able to reverse these trends, very soon we will become conditioned to this new demographic, just as smoking was considered “normal” in the 1960s.
To prevent the burden of diabetes, heart disease, arthritis and cancer that will arise from these trends, we need strong and wide-reaching action to drive decreases in energy consumption, particularly within Australia’s vulnerable population groups.
This is the first part of our series Obese Nation. To read the other instalments, follow the links below:
Part two: Explainer: overweight, obese, BMI – what does it all mean?
Part three: Explainer: how does excess weight cause disease?
Part twelve: Putting health at the heart of sustainability policy
Part thirteen: Want to stop the obesity epidemic? Let’s get moving
Part fourteen: Fat of the land: how urban design can help curb obesity