For anyone who’s ever tried to outrun a junk-food habit, science may have some encouraging news. A new study in Brain Medicine, conducted in Ireland, has uncovered that regular exercise can counteract the depression-like effects of a Western-style “cafeteria” diet high in fat and sugar, at least in rats.
The team found that voluntary running reversed mood-related changes tied to poor diet, thanks to shifts in gut-derived metabolites and hormones that link the body and brain. According to the authors, exercise appears to protect mood by restoring metabolic balance in the gut–brain connection.
“Exercise has an antidepressant-like effect in the wrong dietary context, which is good news for those who have trouble changing their diet,” said Professor Julio Licinio, stated in a recent press release.
When Exercise Meets a Junk-Food Diet
To test how food and movement interact, researchers fed adult male rats either standard chow or a rotating cafeteria diet, high in sugar and fat; half of each group had continuous access to running wheels. The intervention ran 7.5 weeks across four groups with voluntary wheel running.
After just under two months, sedentary rats on the cafeteria diet showed more despair-like behavior, higher insulin and leptin, and broad shifts in gut chemistry. Exercise curbed cafeteria-diet weight gain, reduced fat depots, and blunted those hormonal changes.
The cafeteria diet shifted the gut metabolome widely (100 of 175 measured metabolites in sedentary rats), while exercise altered a small subset. Exercise partially restored three metabolites – substances produced during metabolism – that were tied to mood regulation, which dropped with the cafeteria diet.
Interestingly, while running improved overall brain health, the cafeteria diet dulled one of exercise’s biggest benefits: neurogenesis, or the formation of new neurons in the hippocampus. Rats on the healthier diet experienced a strong neurogenic boost from exercise, while those eating junk food did not, suggesting that diet quality may determine how much the brain benefits from movement.
Read More: It Doesn’t Matter What Time You Exercise As Long As You Get Moving
The Gut–Brain Connection
The research reveals one way exercise keeps the mind resilient even on a poor diet: resetting the gut’s chemical balance. Running restored key compounds involved in serotonin and amino acid metabolism — molecules that help regulate mood and communication between the gut and brain.
This gut-level recalibration may be what allows physical activity to protect mental health, even when eating habits fall short.
Why Diet Still Matters, Even When You Exercise
The study highlights a nuanced truth about the relationship between diet, exercise, and the brain: while physical activity can lift mood even in the context of poor nutrition, the brain’s ability to grow and adapt may still depend on what we eat. This suggests that exercise alone can’t fully restore the neuroplastic benefits that a healthy diet supports.
This opens up new questions about how to best combine lifestyle interventions. Future research will explore whether changes in diet and exercise order, or longer, sustained programs, can amplify these effects. The team also points to several gut-derived compounds as possible biomarkers or therapeutic targets for mood disorders.
Though the experiments were conducted in male rats, the implications reach beyond the lab. As scientists continue to decode the gut-brain connection, this research adds to a growing body of evidence showing how movement and metabolism work together to shape mental health. For now, even if your diet isn’t perfect, getting up and moving remains one of the most powerful tools for keeping your mind, and your microbiome, in balance.
This article is not offering medical advice and should be used for informational purposes only.
Read More: Is 30 Minutes of Exercise a Day Enough?
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