Regular exercise such as running may help protect mental health from the negative effects of eating junk food, a new study from University College Cork in Ireland has found. The research identified how physical activity can counteract behavioural changes linked to diets high in fat and sugar, which are known to affect mood and brain function.
Published in the journal Brain Medicine, the study explored how exercise interacts with metabolism and the gut to influence mental well-being. Researchers focused on how voluntary running affected rats that were fed a Western-style diet rich in high-fat and high-sugar foods. The findings showed that regular exercise helped reverse depression-like behaviours caused by the unhealthy diet.
The team, led by Professor Yvonne Nolan, said the results highlight how lifestyle changes can be tailored to improve mental health at a time when consumption of ultra-processed foods is rising globally. In their experiment, adult male rats were given either a standard diet or a rotating cafeteria-style diet for over seven weeks. Half of the animals in each group were provided access to running wheels to simulate voluntary exercise.
The study showed that rats on the unhealthy diet developed behaviours similar to depression. However, those that exercised regularly displayed marked improvements, suggesting that physical activity can offset the emotional and behavioural impact of poor diet choices. The researchers found that exercise also influenced key metabolic pathways in the body and the gut.
Analysis revealed that the high-fat, high-sugar diet disrupted nearly 100 of 175 measurable metabolites in the gut. Exercise, by contrast, had a more selective effect, correcting some of these imbalances. Among the most notable metabolites affected were anserine, indole-3-carboxylate and deoxyinosine, all of which are associated with mood regulation. These compounds, which declined significantly under the junk food diet, were partially restored in animals that exercised regularly.
In addition to mood changes, the researchers assessed the animals’ memory and learning abilities. Although the junk food diet did not severely impair cognitive performance, the rats that exercised showed modest improvements in spatial navigation and reduced anxiety-like behaviour.
The study suggests that physical activity supports mental health regardless of diet quality, but its full benefits may depend on maintaining a balanced nutritional intake. The researchers said that combining healthy dietary choices with regular exercise could enhance brain resilience and improve mood regulation.
The findings underscore the biological connection between diet, exercise, and emotional well-being, pointing to potential strategies for preventing mood disorders in populations with high consumption of processed foods.
