How bad is junk food for you, really?

By Olivia Henry, the Australian Science Media Centre

Consuming more junk foods, such as soft drinks, packaged snacks, and sugary cereals, is associated with a higher risk of more than 30 different health problems – both physical and mental – according to researchers.

A study, known as an umbrella review, combined the results of 45 previous meta-analyses published in the last three years, representing about 10 million participants.

Thirty-two different poor health outcomes were found to be linked to the consumption of ultra-processed foods (UPFs), with varying levels of evidence supporting the findings.

The researchers found the most convincing evidence around higher ultra-processed food intake, which was associated with a 50% increased risk of cardiovascular disease-related death, a 48-53% higher risk of anxiety and common mental disorders, and a 12% greater risk of type 2 diabetes.

Evidence marked as ‘highly suggestive’ included a 21% increase in death from any cause, a 40-66% increased risk of a heart disease related death, obesity, type 2 diabetes, and sleep problems, as well as a 22% increased risk of depression.

The review also found there may be links between ultra-processed food and asthma; gastrointestinal health; some cancers; and other risk factors such as high blood fats and low levels of ‘good’ cholesterol, but the researchers note this evidence is limited.

Junk food linked to gut inflammation

Dr Daisy Coyle from the George Institute for Global Health in Sydney, who was not involved in the research, says the statistics are “staggering.”

“Ultra-processed foods, laden with additives and sometimes lacking in essential nutrients, have become ubiquitous in the Australian diet,” she says.

“In fact, they make up almost half of what we buy at the supermarket. While not all ultra-processed foods are linked to poor health outcomes, many are, particularly sugary drinks and processed meats.”

While the findings are in line with other research that highlights the health risks associated with UPFs, some experts have pointed out that the study is observational, and therefore can’t prove the ultra-processed foods cause these health issues. It can only show an association.

“While these associations are interesting and warrant further high-quality research, they do not and cannot provide evidence of causality,” The University of Sydney’s Dr Alan Barclay told the AusSMC.

“By their very nature, observational studies are renowned for being confounded by numerous factors – both known and unknown.”

Clare Collins, Laureate Professor at the University of Newcastle agreed, but added that it’s difficult to conduct dietary studies like this in a different way.

“The studies are observational, which means cause and effect cannot be proven and that the research evidence gets downgraded, compared to intervention studies,” she says.

“The problem is that it is not ethical to do an intervention study lasting for many years where you feed people lots of UPF every day and wait for them to get sick and die.”

For now, researchers seem to agree that it can’t be a bad thing to minimise UPF intake.

The review suggests a need for policies that pull consumers away from ultra-processed foods, such as advertising restrictions, warning labels, bans in schools and hospitals. It also calls for measures that make healthier foods more accessible and affordable.

Dr Charlotte Gupta from Central Queensland University suggests that this is issue of accessibility is particularly relevant for shift workers such as doctors, nurses, firefighters, taxi drivers, miners, and hospitality workers.

“There is a lack of availability of fresh foods or time to prepare any food, and so ultra-processed foods have to be relied on (e.g. from the vending machine in the hospital),” she said.

“This highlights the need for not only individuals to try reducing ultra-processed foods in our diet, but also for public health actions to improve access to healthier foods.”

First published in Deadline, Australian Science Media Centre.

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