News
New research suggests Exercise helps Protect the Brain from Junk Food
Can regular exercise help protect your mental health, even if your diet is far from ideal?
- New study suggests demonstrates that exercise can mitigate depression-like behaviours induced by high-fat, high-sugar diets.
- Positive effects of exercise on the brain’s ability to grow new neurons were blocked by the poor-quality diet.
A new study led by Professor Yvonne Nolan and her team at APC Microbiome Ireland, a Research Ireland Centre at University College Cork suggests it can. The research explores how physical activity interacts with a typical Western-style diet that is high in sugar and saturated fats. The results show that while diet still plays a crucial role in brain health, exercise alone can deliver noticeable mood benefits, even under poor dietary conditions.
In the pre-clinical study, subjects were given either a standard healthy diet or a highly processed diet that mimics the fast food commonly eaten in modern societies. Subjects from each group also had access to exercise equipment. After seven weeks, the researchers examined their behaviour, hormone levels, brain chemistry, and the composition of chemicals in their gut.
Lead author Prof Yvonne Nolan says “one of the most striking observations was that exercise helped to counteract the depression-like behaviour caused by the highly processed diet. Subjects on the poor-quality diet who had no access to exercise showed depressive-like behaviour but animals on the same diet who exercised regularly showed antidepressant-like behaviour, suggesting that physical activity may be beneficial even when consuming a Western style diet. This finding is especially important because it shows that exercise can benefit mental health, even if a person finds it difficult to change their diet immediately.”
The benefits of exercise extended to the body’s hormone systems as well. The unhealthy diet caused rises in insulin and leptin levels, both of which are linked to weight gain and mood disorders. These levels were significantly reduced in the subjects that exercised. Exercise also raised the levels of beneficial hormones such as GLP-1 and PYY, which are involved in regulating appetite and energy balance. However, these positive hormonal shifts were less pronounced in the subjects fed the unhealthy diet, indicating that while exercise helps, a better diet can boost its effects even further.
Another important part of the study looked at how diet and exercise influenced the gut microbiome. The researchers found that theunhealthy diet significantly changed the profile of gut metabolites, which are chemical byproducts produced by bacteria in the intestines. Exercise helped to restore the levels of three key gut-derived molecules: anserine, indole-3-carboxylate, and deoxyinosine. These compounds are thought to play roles in brain function, stress resilience, and mood regulation. Although these changes alone did not predict behaviour, they suggest possible targets for future interventions and reinforce the growing understanding of the gut-brain connection.
Perhaps the most unexpected finding was that the positive effects of exercise on the brain’s ability to grow new neurons was blocked by the poor-quality diet. In subjects that ate a healthy diet, exercise led to a robust increase in the production of new neurons in the hippocampus, a brain region important for memory and emotion. But this increase was not observed in subjects that exercised while eating the unhealthy diet. This suggests that the brain’s ability to adapt and grow in response to exercise is strongly influenced by the nutritional environment.
Co first author Dr Sarah Nicholas says “Even when the diet is far from perfect, exercise can help protect mood and mental wellbeing. It supports hormonal balance and partially restores healthy gut chemistry. At the same time, improving diet quality can significantly enhance the brain’s ability to respond to physical activity. For those struggling to make lifestyle changes, this research suggests a practical starting point.”
Dr Minke Nota, also co first author says “Begin with movement. Walking, cycling, or light exercise can begin to shift your biology in a positive direction. As your body responds, small improvements in diet can then build on that momentum. This approach brings mental and physical health into closer alignment and highlights the powerful connection between the gut, the brain, and the choices we make every day.”
'Exercise mitigated a cafeteria diet–induced increase in immobility in the forced swim test and exerted a modest anxiolytic effect irrespective of diet' is available to read online at Brain Medicine.
DOI: 10.61373/bm025a.0116
