How natural experiments can inform Australia’s obesity policy

Introduction by Croakey: Like many other countries, Australia has experienced a sharp increase in obesity rates over the past 30 years. This has increased the risk of a range of serious illnesses and costs our health system an estimated $6 billion a year.

It’s difficult both practically and ethically to run trials of policy options to address obesity, but natural experiments can help fill the knowledge gap for governments and policy makers.

Below, Peter Breadon, Director of the Health Program at Grattan Institute and lead author of the recent Grattan report, ACDC: Highway to health, reports on some international examples of natural experiments that provide valuable information on the policy changes that could make a difference to our rising rates of overweight and obesity, including evidence supporting the impact of a sugar-sweetened beverages tax.

This article was originally published in Pearls and Irritations and is re-published here with permission.

Peter Breadon writes:

When a government proposes a policy to improve our diet, it can trigger a gag reflex. Some people feel that deciding what to eat is purely a personal choice, and the ‘nanny state’ should stay out of the way. No-one wants to be lectured, shamed, or forced to eat their greens. Perhaps it goes all the way back to battles for autonomy when we were toddlers, strapped into a high-chair and being force-fed peas.

Former Prime Minister (and former Health Minister) Tony Abbott summed up this view best when he said: “The only person responsible for what goes into my mouth is me, and the only people who are responsible for what goes into kids’ mouths are the parents.” Whether it’s a banana, a packet of chips, or even eating a raw onion on television, it’s totally up to you.

If only this were true. It’s confronting to realise that we’re not masters of our own destiny. But so-called natural experiments show that we are products of our environment, even when we think we’re in control.

Unlike planned experiments, natural experiments happen spontaneously in real-life settings. A change happens to one group of people and not another. One city, state, or country might adopt a new policy, while others don’t. Or fast-food restaurants might open in one group of suburbs, but not another. Then we can see what happens. If the populations are otherwise similar, but start to get different outcomes, it might tell us that the policy, or the restaurants, are the reason.

The power of natural experiments

Natural experiments play out in the real world, often on a large scale, and can measure risks and outcomes that no researcher could ethically test in a trial. That makes them a powerful lens on complex systems. They have generated many insights, and saved countless lives, since they were pioneered nearly 200 years ago.

It started in 1854, as a wave of cholera was killing Londoners. Two outbreaks in the previous 25 years had killed almost 15,000 people. A doctor named John Snow mapped the deaths and found that they were clustered around the water pump on Broad Street. People using that water pump were far more likely to die than people living a few blocks away, who used other pumps.

A natural experiment had revealed the source of the problem: contaminated drinking water. When Dr Snow told the local authorities about his findings, the pump handle was removed the next day.

Natural experiments have come a long way. In 2021, the Nobel Prize was awarded to three economists for making them a mainstream research method. Some of their findings helped overturn economic orthodoxy and accepted wisdom. For example, they showed that migrants didn’t necessarily suppress wages, and that higher minimum wages didn’t necessarily reduce jobs. Natural experiments can challenge natural assumptions.

A mind shift needed

We need a similar mindset shift when it comes to food and health.

In the past 30 years, the rate of obesity has tripled in Australia. It’s been a gradual but relentless change and the consequences are hard to overstate. Since obesity increases the risks of a range of serious illnesses, such as diabetes, cancer, and heart disease, the cost is enormous: perhaps $6 billion a year in healthcare costs, and well over $13 billion in annual cost to the broader economy.

And those dry financial statistics gloss over the human toll: hundreds of thousands of years of life lost.

Who or what is responsible for this obesity pandemic? A typical instinct is to blame the individual, branding them as ‘lazy’ or lacking willpower. That results in stigma and discrimination, which create their own risks to health and wellbeing. But the personal responsibility theory doesn’t stack up. It’s hard to believe there was a collective loss of interest in being healthy, or a national crisis of willpower, that led to obesity tripling in a generation.

Something deeper must have changed, and natural experiments help to confirm this. One recent example shows how small changes around us can change our choices and change our health.

The case for a sugar-sweetened beverages tax

There are taxes on sugar-sweetened beverages in 85 countries, ranging from France, to Finland, to Fiji – but not Australia. There is good evidence that these drinks lead to weight gain, and they have limited or no nutritional benefits.

But does a small increase in the price of soft drinks really lead to people drinking less soft drink? And will that lead to improvements in health, or will people just get more sugar elsewhere?

Like many prevention policies, a tax on sugar-sweetened beverages will take time to achieve its full impact. It takes time for diet to translate into obesity, and it takes time for obesity to cause diseases. But one recent natural experiment suggests that taxes on these drinks might start getting results almost immediately.

Since 2015, several US cities have introduced taxes on sugary drinks. A recent study looked at data on more than five million births in the US. It compared outcomes for mothers and babies in cities with and without a sugary drinks tax. In cities with the tax, rates of gestational diabetes fell by about 40 per cent, as did the rate of babies that were small for their age. The falls were bigger in Philadelphia, where the tax was higher.

Impacts like that are life changing. Gestational diabetes increases risks for mothers and babies during pregnancy and childbirth, including serious birth complications. And the risks to mothers and babies endure, including developing type 2 diabetes and cardiovascular disease later in life.

No single study is definitive, and all studies have limitations, but this finding does align with other evidence. A review of 86 studies from around the world found that sales of sugary drinks fell after taxes were introduced. And the link between these drinks and diabetes has been demonstrated.

So it makes sense that sugary drink taxes would lead to healthier mothers and babies. A big impact makes sense too. The same groups at higher risk of gestational diabetes – poorer people and disadvantaged ethnic groups – are more likely to drink sugary drinks, and more likely to stop due to higher prices.

A study from Norway

Another ingenious study of a natural experiment was published this year. Again, it reveals a link between diet and health, but this time in a very different country.

The number of fast-food restaurants in Norway quintupled from 1980 to 2007. Norway has compulsory national service for men, so every male has their height, weight, and cognitive test scores recorded around the age of 18. Researchers linked these two sets of data to see if growing up near fast-food restaurants makes a difference.

They found that it does. Living near fast-food restaurants was linked to being overweight, and the impact was big. It could account for about a third of all the weight gained in Norway over three decades, a period when rates of obesity soared. Even more alarmingly, living near fast-food outlets was linked to lower scores on intelligence tests, and to lower academic attainment.

You might be thinking that the fast-food outlets aren’t to blame. Perhaps they just open in poorer neighbourhoods, places where kids were already overweight and doing badly in school. The researchers thought of that. They checked if the impact was different for different kinds of families, based on things like the parents’ income, education, marital status, and even the father’s weight. They looked at the characteristics of the neighbourhood too.

None of that made much difference. On average, growing up near fast-food increased the risk of being overweight for children from rich families and poor families alike. For cognitive test scores there was one difference. Scores were lower for all kinds of children, but the difference was much greater for kids whose fathers had less education, compounding existing disadvantage.

We don’t live in a vacuum

These examples help hammer home the reality that we don’t live in a vacuum. Compared to previous generations, we eat more unhealthy foods, which are more heavily promoted, and which manufacturers continually tweak to make as appealing as possible. We are what we eat, and to a large extent we eat what’s convenient, cheap, and appealing – and those usually aren’t the healthy options.

If a slightly higher price for a can of soft drink, or growing up near a fast-food outlet, can make a difference to our health, think of all the other things in our environment that can do just as much, and even more, to influence us. Junk-food advertising, the availability and cost of public transport, the price of fresh fruits and vegetables, how much salt and trans fatty acids are in manufactured foods … the list is long.

Those factors add up. Two-thirds of Australian adults are now overweight or obese. Unless you’re lucky enough to have the genes or the money to fight the environment, that’s probably how you’ll end up: overweight or obese, with a higher risk of sickness, disability, and dying earlier.

Treating diet as purely a matter of personal choice sounds sensible, until you realise that not taking action changes people’s choices too, even as the risks pile up. Policy changes really can reshape our diets – and our waistlines. Not making those changes is a choice, which in turn influences everyone’s choices about what they put in their mouth, to use Tony Abbott’s phrase.

Moving on from the myth of the immaculate individual will take a shift in policy. Australia lags far behind leading countries when it comes to making common-sense rules and regulations about food.

But polling suggests strong support for government action. Half of us think there should be more regulations and policies to help people be healthy, while less than one in 10 say there are too many.

While we often blame the individual for obesity, we intuitively know that most people don’t have the time, knowledge, and patience to consistently make healthy choices without some guides and guardrails in place. But there’s little sign that those policies are on the way.

Budgetary gaps

The recent federal Budget made welcome investments in preventive health. It will be free to get vaccinated at your local chemist. The Government will crack down on vaping, raise the tax on tobacco, and provide more services to help people quit. And an Australian Centre for Disease Control (ACDC) will be established, giving Australia a new agency dedicated to stopping disease before it starts.

But hardly any funding in the Budget will help shift our diets.

We should keep extending the prevention triumphs of the 20th century – tackling tobacco and increasing vaccination – but it’s time to get serious about food.

The ACDC should make improving what we eat one of its top priorities. And governments should commit funding to implement what the ACDC recommends. That way we can take the blame off individuals and start to re-balance the scales, making it easier for Australians to make healthy choices.

See here for Croakey’s archive of stories on obesity.