High-Fat Diets Linked to Anxiety Through Changes in Gut Microbiome and Brain Serotonin Systems

Individuals with obesity are more likely to experience anxiety and other mental health disorders. 

Among various overlapping factors, high-fat diets have been identified as a possible contributor to both obesity and anxiety. These diets can also change the composition of our gut microbiome. 

The gut microbiome might be the key link, as it may influence obesity-related metabolic factors and affect anxiety-like behavior through the microbiota-gut-brain axis. These connections could help explain, in part, why obesity and anxiety can often occur together. 

The study analyzed shifts in the gut microbiome, microbiome-gut-brain axis, and serotonin (serotonergic) systems in the brain. These systems are known to influence both anxiety and metabolism. This may ultimately impact brain chemicals associated with anxiety. 

The findings are published in BMC Biological Research. Researchers from the University of Colorado Boulder explored how high-fat diets affect gut microbiome composition and diversity, brain serotonin systems, and anxiety-like behaviors. Weekly fecal samples were collected to analyze gut microbiome changes, and behavioral tests were conducted at the end of the study. 

The researchers also measured changes in body composition related to diets, including final body weight, weight gain, and adiposity (body fat). 

Additionally, the high-fat diet group exhibited increased expression of genes related to serotonin production and signaling within the brainstem’s dorsal raphe nucleus. 

Although serotonin is often regarded as a “happy chemical,” certain serotonin neurons can trigger temporary fear or anxiety-like behavioral responses when activated, the study authors explained. 

The findings suggest that high-fat diets alter gut microbiome composition in ways associated with increased body fat and weight and changes in brain serotonin systems related to anxiety. Researchers noted that a high-fat diet tends to reduce the overall diversity of the gut microbiome, leading to a less complex microbial community which can impair the gut’s ability to maintain a balanced environment. Serotonin is primarily produced in the gut, with about 95% of the body’s serotonin found in the gastrointestinal tract. 

While the study’s findings offer insight into potential therapeutic interventions for mental health, the mechanisms underlying the observed changes were not directly investigated. The present study also has other notable limitations, such as exclusively including male rats of certain ages, which raises questions about the findings’ applicability to females or other life stages.