Scientists have discovered a ‘unique’ effect of a high-fat diet on anxiety via the gut-brain axis.

When stressed, many people reach for comfort foods high in fat and sugar. However, a recent study from the University of Colorado Boulder suggests that this coping mechanism may be counterproductive. published in the journal Biological researchstudies have found that a diet high in animal fat disrupts gut bacteria, alters behavior, affects brain chemicals, and causes anxiety.

The motivation for this study comes from the growing recognition of the gut-brain axis, the complex communication network that connects the gastrointestinal tract and the brain. Researchers are increasingly interested in how this connection affects mental health through our gut microbiome, the trillions of bacteria that live in our guts. Previous research has shown that the composition of gut bacteria can have a significant impact on physical and mental health, including obesity, anxiety and depression.

Given the frequent and increasing prevalence of obesity and anxiety disorders, researchers set out to investigate whether diet may be a common factor contributing to both conditions. Specifically, they wanted to investigate whether the high-fat diet common to modern diets can affect the gut microbiome on brain function and behavior. Understanding these mechanisms may provide insight into how dietary choices affect mental health and may offer new avenues for treatment and prevention.

To investigate these questions, the researchers conducted a controlled experiment using adolescent rats, whose developmental stage is similar to that of human adolescence, a critical period for establishing long-term dietary and health patterns.

Rats were divided into two groups. One group was fed a standard diet containing about 11% fat, while the other group was fed a high-fat diet, mainly saturated animal fat, containing 45% fat. The duration of the dietary intervention was nine weeks, which is a significant part of a rat’s life span, equivalent to several years in humans.

During the study, researchers collected weekly stool samples from both groups of rats to monitor changes in gut microbiota. These samples were analyzed to assess the diversity and composition of gut bacteria, focusing on the balance between Firmicutes and Bacteriidetes, two major bacterial groups thought to influence diet and health outcomes.

After nine weeks on the diet, the rats underwent a series of behavioral tests designed to measure anxiety-like behavior. These tests included the elevated plus maze, which assesses anxiety based on the rats’ willingness to explore an open, raised arm, and other tests that measure stress and response to novel environments. The researchers also examined the rats’ brains to measure the expression of specific genes involved in serotonin production and signaling.

The first discovery was that rats fed a high-fat diet had significantly different gut microbiota profiles than those fed a standard diet. Specifically, a high-fat diet led to a decrease in gut bacterial diversity, which is generally associated with poorer health outcomes. The ratio of Firmicutes to Bacteroides increased in the high-fat diet group, indicating a change in balance often associated with obesity and metabolic disorders.

Behavioral assessments showed that rats fed a high-fat diet exhibited more anxiety-like behavior than those fed a standard diet. This was particularly evident in high-fat-fed rats, where they were less inclined to explore open, elevated spaces, and in tests such as the elevated maze, indicating higher levels of anxiety. These behavioral changes suggest that changes in the gut microbiome induced by the high-fat diet directly affected the rats’ anxiety-related responses.

“Everyone knows these are not healthy foods, but we feel strongly about gaining a little weight,” says Christopher Lowry, a professor of integrative physiology at the University of Colorado Boulder. “If you realize that they also affect your brain in ways that cause anxiety, that makes the risk even higher.”

At the molecular level, studies have found that high-fat diets affect the expression of certain genes involved in serotonin production and signaling in the brain. The high-fat diet group showed increased expression of genes such as tph2, htr1a, and slc6a4 in the dorsal raphe nucleus of the brainstem. These genes are involved in the production and signaling of serotonin, a neurotransmitter commonly associated with feelings of well-being and happiness. However, increased expression of these genes may be associated with anxiety, suggesting that a high-fat diet may have created a brain chemical environment conducive to anxiety.

“It’s unusual to think that a high-fat diet would change the expression of these genes in the brain,” Lowry said. “The high-fat group basically had higher anxiety molecular markers in their brains.”

The researchers hypothesize that disruption of the gut microbiome damages the gut lining, allowing bacteria and their metabolites to enter the bloodstream and communicate with the brain via the vagus nerve. This gut-brain communication pathway affects brain activity and contributes to anxiety-like behaviors. The results of the study show that a diet high in fat not only has negative effects on physical health, such as weight gain and changes in gut bacteria, but it also has a significant impact on mental health through changes in brain chemistry.

A limitation of the study is the reliance on animal models that may not fully replicate human physiology and behavior. Future research should aim to confirm these results in human subjects, investigate specific mechanisms of gut-brain communication, and investigate the effects of different types of dietary fat.

“Given the early introduction of high-fat foods into childhood diets and the increasing prevalence of obesity, we present a scenario in which adolescent diet may influence the gut microbiome, brainstem serotonergic system, and susceptibility to obesity. development of mental disorders in adulthood. “This knowledge may lead to new microbiome-based approaches to prevent stress-related mental disorders such as anxiety,” the researchers concluded.

“High-fat diet, microbiome-gut-brain axis signaling, and anxiety-like behavior in male rats” by Silvana IS Rendeiro de Noronha, Lauro Angelo Gonçalves de Moraes, James E. Hassell, and Christopher. E. Stamper, Matthew R. Arnold, Jared D. Heinze, Christine L. Fox, Margaret M. Lieb, Christine E. Clair, Bree L. Carnes, Sophia Jackel, Kelsey M. Lupi, Fernanda Silva, Dioclecio Alves Cianca- Jr. , Christopher A. Lowry and Rodrigo Cunha de Menezes.