A new study led by researchers at University College Cork and APC Microbiome Ireland has uncovered how exercise can help protect mental health, even when people eat a Western-style junk food diet.
The findings were published in the journal Brain Medicine and show that running exercise can reduce depression-like symptoms caused by eating high-fat, high-sugar foods.
The research also explores the gut-brain connection, suggesting that certain chemicals produced in the gut may explain why exercise benefits mood.
The study was conducted on adult male rats. Some rats were fed a standard healthy diet, while others received a “cafeteria diet” made up of high-fat and high-sugar foods, similar to ultra-processed Western diets.
Half the animals in each group had access to running wheels, allowing the researchers to see how exercise affected brain and body health under different diet conditions.
The most important finding was that running had clear antidepressant-like effects in rats that ate the unhealthy cafeteria diet. Even though the diet caused negative mood behaviors, exercise was able to reduce these effects.
The researchers believe this is good news for people who struggle to change their diets but want to improve their mental health through exercise.
To better understand how this works, the scientists looked at the chemicals in the gut and blood. They found that the cafeteria diet changed many substances in the gut, but exercise helped correct some of these changes.
In particular, three gut chemicals—anserine, indole-3-carboxylate, and deoxyinosine—were lowered by the junk food diet but brought back up by exercise. These chemicals are linked to mood and brain function.
The team also studied how the diet and exercise affected hormones in the blood. The cafeteria diet caused big increases in insulin and leptin—hormones tied to metabolism and appetite.
However, these levels were lower in rats that exercised, even if they still ate the junk food. Some other hormones were also affected. For example, exercise raised peptide YY (PYY) levels in junk food-fed rats, which may help the body cope better with the diet’s effects.
One surprising result came from looking at the brain. In rats that ate the healthy diet, running led to more new brain cells in the hippocampus, a region involved in memory and mood. But this benefit was blocked in the rats on the cafeteria diet.
This means that while exercise still improved mood, the diet may have stopped the brain from gaining its full benefits from exercise.
The study also found strong links between certain gut chemicals and how the rats performed on mental tests. Some substances were associated with worse thinking skills, no matter what diet or exercise group the rats were in. This adds to the growing evidence that the gut plays a big role in brain health.
An editorial published with the study said this is promising for people who eat poorly but still want to feel better. The research shows that even if people can’t fix their diet right away, they can still benefit mentally from being physically active.
There are some limitations. The study only looked at male rats, so more research is needed in females. The study also lasted just over seven weeks, and longer-term effects are still unknown. Still, this research opens the door to better understanding how lifestyle changes affect mental health.
Scientists also believe some of the gut chemicals found in the study could one day be used as treatments for depression or as warning signs that someone is at risk. This study gives hope that even in our modern world of processed food, simple habits like exercise can have a big impact on mood and mental well-being.
If you care about mental health, please read studies about cannabis use disorder linked to increased risk of mental diseases and some mental health drugs can cause rapid weight gain.
For more health information, please read studies that one sleepless night can reverse depression for days and scientists find better treatment for older adults with depression.
The study is published in Brain Medicine.
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