High levels of physical activity don’t cancel out the long-term health risks of a poor diet, according to new research led by the University of Sydney. 

The study, published in the British Journal of Sports Medicine, highlights the importance of adhering to both physical activity and dietary guidelines to significantly reduce the risk of early death. 

What did the study find?

Researchers analysed data from more than 360,000 adults enrolled in the UK Biobank, a large-scale biomedical cohort study collecting detailed lifestyle and health information from British participants. 

They looked at the independent and combined effects of diet and physical activity on all-cause, cardiovascular, and cancer-related mortality. 

The results showed that individuals who maintained both a high-quality diet and high levels of physical activity had the lowest mortality risk – 17% lower for call-cause death, 19% for cardiovascular disease, and 27% for certain cancers – compared to participants who were inactive and ate poorly. 

Debunking the notion that exercise alone is enough

Lead author Associate Professor Melody Ding from the Charles Perkins Centre and the Faculty of Medicine and Health at the University of Sydney, says the findings debunk the notion that exercise alone is enough to mitigate poor dietary choices. 

“Both regular physical activity and a healthy diet play an important role in promoting health and longevity,” she says. 

“Some people may think they could offset the impacts of a poor diet with high levels of exercise or offset the impacts of low physical activity with a high-quality diet, but the data shows that, unfortunately, this is not the case.”

What constitutes a high-quality diet? 

In the study, a high-quality diet was defined as one that included at least 5 serves of fruit and vegetables per day, 2 serves of fish per week, and minimal red and processed meat.

Implications for long-term health

Co-author Joe Van Buskirk, from the School of Public Health, Faculty of Medicine and Health, emphasises the combined benefits of a quality diet and sufficient physical activity. 

“Adhering to both a quality diet and sufficient physical activity is important for optimally reducing the risk of death from all causes, cardiovascular disease and cancers,” he says. 

While earlier studies have suggested that high-intensity exercise may offer short-term physiological protection from the effects of over-eating, this new research confirms that long-term health outcomes depend on consistent adherence to both good nutrition and regular movement. 

“This study reinforces the importance of both physical activity and diet quality for achieving the greatest reduction in mortality risk,” says Associate Professor Ding.

“Public health messages and clinical advice should focus on promoting both physical activity and dietary guidelines to promote healthy longevity.”