A new study from University College Cork, led by Professor Yvonne Nolan and published October 21, 2025, in Brain Medicine, purports to show exercise can reduce depression-like behaviors caused by a high-fat, high-sugar Western diet.
Researchers fed male rats either a healthy diet or a high-fat, high-sugar “cafeteria diet” for seven weeks. Half of each group had access to a running wheel. Rats on the junk food diet showed depression-like behaviors, but those who ran appeared happier and less anxious, despite eating poorly. Exercise altered the body’s chemistry to improve mood.
This next part is summarized by AI. I can’t pretend to understand metabolites, leptin levels, and peptides.
The junk food diet disrupted 100 of 175 gut metabolites, chemicals produced by gut microbes. Three mood-related metabolites (anserine, indole-3-carboxylate, and deoxyinosine) dropped with the bad diet but rose with exercise. Blood tests showed running lowered high insulin and leptin levels caused by the diet, stabilizing mood. Other hormones, like peptide YY, helped balance metabolism in exercising rats on the poor diet.
Exercise typically boosts new neuron growth in the hippocampus, a brain area linked to emotion and memory. In rats on a healthy diet, running increased this growth. The junk food diet blocked this benefit, but exercise still improved mood, showing its power even with dietary setbacks.
This research proves you don’t need a perfect diet to boost mental health.
An accompanying editorial by Professor Julio Licinio and colleagues emphasizes the clinical relevance of these findings, noting that “exercise has an antidepressant-like effect in the wrong dietary context, which is good news for those who have trouble changing their diet.” The editorial highlights how this research provides a biological framework for understanding why exercise remains beneficial even when dietary improvements prove challenging to implement.
Science Daily
This is great news if changing your diet is tough. Start moving to lift your mood, no matter what’s on your plate.
The study, conducted on male rats, needs further exploration with female subjects and longer timeframes. Specific gut metabolites could become targets for mood disorder treatments. For now, exercise is a practical way to combat the mental toll of a junk-heavy diet.
It’s easy to take action. Add 30 minutes of movement, like walking or running, to most days. Consistency matters more than intensity.
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