Researchers have pinpointed specific metabolic pathways through which exercise counterbalances the negative behavioral effects of consuming a Western-style cafeteria diet. In a new study, voluntary running exercise was effective at mitigating depression-like behaviors induced by high-fat, high-sugar diets that impact circulating hormones and gut-derived metabolites.
Adult male rats in the study were fed either “standard chow” or a “rotating cafeteria diet” that consisted of various high-fat and high-sugar foods for seven and a half weeks. Half of each dietary population had access to running wheels.
This experimental design isolated the independent and combined effects of diet quality and physical activity on brain function and behavior.
An accompanying editorial by Julio Licinio and colleagues from the US researcher publisher Genomic Press emphasizes the clinical relevance of these findings, stressing that “exercise has an antidepressant-like effect in the wrong dietary context, which is good news for those who have trouble changing their diet.”
Dynamics of exercise and mood regulation
The research suggests that physical activity may be beneficial for humans’ mental health when consuming a poor-quality diet, similar to the rats who engaged in voluntary wheel running.
Professor Yvonne Nolan at University College Cork, APC Microbiome Ireland, and colleagues used untargeted metabolomics to analyze the rats’ cecal contents, revealing that the cafeteria diet dramatically altered the gut metabolome, impacting 100 out of 175 measured metabolites in sedentary animals.
Exercise most noticeably benefitted three metabolites previously linked to mood regulation: anserine, indole-3-carboxylate, and deoxyinosine, which were all decreased by the cafeteria diet but partially restored by exercise.
While the cafeteria diet alone did not critically impair spatial learning or recognition memory in these adult rats, exercise produced “modest improvements” in spatial navigation.
When examining anxiety-like behaviors, the researchers found subtle anxiolytic effects of exercise regardless of which diet the rats were fed.
Hormonal protections
Plasma hormone analysis uncovered striking metabolic changes that reflected the rats’ behavioral changes. The cafeteria diet “substantially elevated” insulin and leptin concentrations in sedentary animals, changes that were significantly reduced by exercise.
Diet quality may fundamentally influence the brain’s ability to benefit from physical activity at the cellular level.First author of the study, Dr. Minke Nota from University College Cork, believes that these hormonal normalizations likely contributed to the protective effects of exercise against diet-induced behavioral changes.
The study also revealed complex interactions between diet and exercise on other metabolic hormones. Exercise increased circulating GLP-1 levels in standard chow-fed animals, but this effect was blunted by the cafeteria diet.
Conversely, exercise raised levels of peptide YY — a gut hormone released after eating that regulates appetite and satiety — only in rats fed the cafeteria diet.
Implications of gut-brain research
Meanwhile, the cafeteria diet prevented the usual health benefits of exercise, specifically by hindering the exercise-induced increase in the formation of new neurons (neurogenesis).
However, for standard chow-fed rats, exercise “robustly increased” neurogenesis across the hippocampus, a brain region involved in emotion and memory.
This finding suggests that diet quality may fundamentally alter the brain’s capacity to benefit from physical activity at the cellular level, note the researchers.
The team completed correlation analyses to identify relationships between specific metabolites and behavioral outcomes.
Several cecal metabolites — such as aminoadipic acid and 5-hydroxyindole-3-acetic acid — were linked to worse cognitive performance, regardless of the experimental diet or exercise. This points to a fundamental link between gut chemistry and brain function.
Study limitations and future directions
The authors of the paper point to several limitations of the study. It was conducted exclusively in male rats, and sex differences in metabolic and neurogenic responses to diet and exercise are well-documented.
Additionally, the seven-week intervention period may not capture longer-term adaptations that could emerge with chronic exposure. The authors say future studies incorporating female animals, longer intervention periods, and dose-response designs could help refine the understanding of these complex interactions.
The research also presents new opportunities to investigate specific metabolites as potential therapeutic targets. “The protective effects of exercise on anserine, indole-3-carboxylate, and deoxyinosine levels suggest these compounds may serve as biomarkers or even therapeutic agents for mood disorders,” highlight the authors.
Societal relevance
The findings published in the peer-reviewed journal Brain Medicine provide important insights into how lifestyle interventions might be optimized to support mental health in an era of widespread ultra-processed food (UPF) consumption.
UPFs are a hot topic in global nutrition, with the US moving toward establishing an authoritative definition for these items, and Malaysia recently joining the list of countries banning junk and UPFs in schools.
International scientists recently speculated that the rise of UPFs has resulted in a diversity of poorer health outcomes in men, stressing that obesity rates and type-2 diabetes have soared, while sperm quality has plummeted over the past 50 years.
