Fast food, screens, and no greens: A recipe for teen health trouble

When a cheeseburger costs less than a punnet of strawberries, it's clear the odds are stacked against healthy choices—especially for teenagers.

Now, new research from the University of South Australia shows that it's not just unhealthy eating habits affecting teens, but an alarming clustering of poor lifestyle choices that's putting the majority of teenagers at serious risk of preventable diseases later in life. The research is published in the journal Nutrients.

In a study of more than 293,770 teenagers aged 12–17, from 73 countries, across five World Health Organization (WHO) regions, researchers assessed habit clustering, including exercise, healthy food consumption and screen time, finding that:

• 85% did not get enough exercise
• 80% did not eat enough fruit and vegetables
• 50% regularly consumed fast food
• 39% had too many soft drinks
• 32% spent excessive time on screens.

Overall, more than 92.5% of teenagers reported two or more unhealthy behaviors, which puts them at increased risk of developing chronic diseases like obesity, heart disease and diabetes.

Specifically, 7% of teenagers reported one unhealthy behavior; 30% of teenagers had two; 36.5% had three; 21.5% had four; and 4.5% had five unhealthy behaviors. Across all WHO regions, less than 1% of teenagers exhibited no unhealthy behaviors.

It's timely research in light of the South Australian government's new "LiveLighter" campaign to tackle obesity.

Lead researcher, UniSA's Dr. Ming Li, says behaviors that are set up in teenage years lay the groundwork for behaviors in adulthood.

"The teenage years are a critical window for growth and development—physically, mentally, and emotionally—and they set the foundation for long-term health," Dr. Li says.

"But with junk food so readily available, and physical activity often replaced by screen time, more teens are picking up multiple unhealthy habits that could lead to serious health issues down the track."

The study found distinct differences between regions. Teenagers in higher-income countries—including the Americas and Eastern Mediterranean—were more likely to report a higher number of unhealthy behaviors, with 13% of teenagers in these regions recording all five risk factors.

While Australian data was not specifically assessed, Dr. Ling says that Australian teenagers would likely report multiple unhealthy lifestyle behaviors, akin to those seen in other high-income countries.

Dr. Li says these trends are driven by broader societal shifts.

"Some of what we see comes down to rapid urbanization, sedentary school environments, and limited access to safe recreational spaces, particularly in low- and middle-income countries," Dr. Li says.

"On top of this, taste preferences, household income, and limited availability of fresh produce—especially in disadvantaged areas—make healthy choices harder to access and maintain."

While the study reports multiple unhealthy lifestyle behaviors for most teenagers, it also finds some protective factors that can help.

"When teenagers have supportive families and a supportive peer group, their risk of having four or more unhealthy behaviors reduces by 16% and 4% respectively," Dr. Li says "Similarly, food-secure households also reduce risk by 9%."

Dr. Li says the findings point to the urgent need for tailored, multilevel strategies that go beyond individual choices to address social and environmental conditions.

"It's clear we need systemic action—better school-based physical activity programs, urban design that gives teens access to green spaces, policies that make healthy food affordable, and limits on junk food marketing to children," Dr. Li says.

"Ultimately, good health needs to be an easier, more accessible choice—not one that requires privilege, planning, and willpower."