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
These connections could help explain, in part, why obesity and anxiety can often occur together.
To delve deeper into the intricate relationships between high-fat diets, obesity, anxiety, and the gut microbiome, a new study investigated the effects of a high-fat diet over 9 weeks on rats.
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.
The results suggest that high-fat-diet-induced obesity may be associated with altered signaling along the microbiome-gut-serotonergic brain axis, leading to increased anxiety-related behaviors in rats.
In other words, obesity caused by a high-fat diet may disrupt gut bacteria and their signaling pathways to the brain. This may ultimately impact brain chemicals associated with anxiety.
The findings are published in
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.
For 9 weeks, they studied two groups of rats:
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 the diets, including final body weight, weight gain, and adiposity (body fat).
Results showed that the rats fed a high-fat diet gained more weight and body fat. They also had significantly lower gut microbiome diversity, which is generally linked to poorer health.
These rats also had a higher
Additionally, the high-fat diet group exhibited increased expression of genes related to serotonin production and signaling within the brainstem’s dorsal raphe nucleus. This area of the brain is linked to stress and anxiety.
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.
Medical News Today spoke with Thomas M. Holland, MD, MS, a physician-scientist and assistant professor at the RUSH Institute for Healthy Aging, RUSH University, College of Health Sciences, who was not involved in the study.
He 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.”
MNT also spoke with Timothy Frie, MS, a nutritional neuroscientist and doctor of health science candidate with a certificate in nutritional psychology from the Center for Nutritional Psychology, who was not involved in the study.
He further explained, “[t]he microbiome-gut-serotonergic brain axis represents a critical communication pathway between the gut microbiota and the brain, particularly focusing on serotonin, a neurotransmitter essential for mood regulation.”
“Serotonin is primarily produced in the gut, with
— Timothy Frie, MS
“The significance of this axis in mental health is profound. Alterations in the gut microbiome can lead to dysregulation of serotonin levels, impacting mood, anxiety, and overall mental health,” Frie said.
For example, he said, an imbalance in the microbial community (gut dysbiosis) can result in increased intestinal permeability, systemic inflammation, and altered serotonin signaling.
According to Frie, this can trigger or worsen mental health conditions such as anxiety, post-traumatic stress disorder, and depression.
“Understanding this axis opens up new avenues for therapeutic interventions targeting the gut microbiome to modulate brain function and improve mental health outcomes,” he said.
“A diet high in saturated fats and low in fiber can reduce bacterial diversity and alter the balance of gut bacteria, similar to the effects seen in rats,” Holland said.
Additionally, he said, “[h]uman studies have shown that diets high in saturated fats and low in healthy nutrients are associated with higher rates of anxiety and depression.”
“The behavioral changes observed in rats provide a potential mechanistic explanation for these associations in humans,” Holland explained.
Frie added that “[w]hile there are inherent differences between rats and humans, many physiological and biochemical pathways are conserved across species.”
“The basic principles of the microbiome-gut-brain axis, as observed in rat studies, provide valuable insights applicable to human health. In both rats and humans, diet-induced changes in the gut microbiome can significantly influence brain function and behavior through similar mechanisms.”
— Timothy Frie, MS
“Human studies have corroborated findings from rodent models, showing that dietary interventions can modulate the gut microbiome, affect serotonin levels, and impact mental health,” he said.
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.
The study authors suggest future research should address these factors, particularly given the higher incidence of anxiety and other mental health disorders in females.
Overall, more research is needed to fully understand the microbiome-gut-serotonergic brain axis and its implications for human health.
“[This study’s] findings underscore the importance of dietary interventions in the treatment of anxiety disorders, particularly for individuals with obesity,” Holland said.
He emphasized, “By improving dietary habits, such as increasing the intake of healthy fats and reducing unhealthy fats, individuals can support better gut-brain signaling, reduce inflammation, and enhance overall mental health.”
Holland specifically recommends increasing the intake of:
Frie similarly advises consuming a diet rich in omega-3s, fermented foods, and fiber from fruits, vegetables, and whole grains to promote the growth of beneficial gut bacteria, enhancing microbial diversity and gut health.
Additionally, both experts highlighted the importance of hydration for overall and digestive health and recommended meeting daily water needs.
“Ensuring adequate fiber intake, including probiotic and prebiotic foods, and maintaining proper hydration will promote a healthy gut microbiome, reduce inflammation, support overall brain health, and improve mood and anxiety levels,” Holland said.
Holland also suggested reducing the intake of high-trans and saturated-fat foods, fast and fried foods, dark red meat, and high-fat dairy products.
“Limiting the intake of high-fat and processed foods helps prevent gut dysbiosis and reduces inflammation, supporting better gut-brain communication,” Frie agreed.
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