A team at University College Cork has found that exercise can help protect the brain from some of the harmful effects of ultraprocessed foods. The study, published in Brain Medicine, uncovered how physical activity influences hormones and gut microbes to improve mood and metabolism, even when diet quality is poor.
Researchers fed adult rats either a standard diet or a “cafeteria diet” made up of fatty, sugary foods similar to those found in a Western-style menu. Half of each group had access to running wheels. After several weeks, the rats on the junk food diet showed higher levels of insulin and leptin, two hormones linked to metabolic stress and mood changes, but those that exercised had much lower levels.
“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, coauthor of an accompanying editorial.
The researchers found that running changed both gut metabolites and brain chemistry. Rats eating the cafeteria diet had reduced levels of several compounds linked to mood regulation, including anserine and indole-3-carboxylate. Exercise partially restored these levels, suggesting that movement may help rebalance microbial and hormonal pathways tied to emotional health.
The benefits did not extend to every part of the brain, however. In animals eating the healthier diet, exercise boosted the formation of new neurons in the hippocampus, a brain region involved in memory and emotion. In those eating junk food, that neuroplasticity response was blunted, showing that diet quality still matters for long-term brain health.
The study’s authors say the findings help explain how lifestyle factors such as diet and exercise work together to shape mood and cognition through the gut-brain axis. While the research was conducted in rats, it offers new insight into how consistent physical activity might buffer the mental and metabolic impact of modern diets high in fat and sugar.
This research was supported by the Irish Research Council, Research Ireland and the Health Research Board. Some authors reported additional funding from Marigot Limited, Yakult, Alkermes plc. and Janssen for unrelated work.