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High-fat diets cause high anxiety through changes in gut bacteria

In stressful times, many of us find comfort in high-fat junk food. However, recent research suggests that this common coping mechanism might be doing more harm than good.

A new study from the University of Colorado Boulder has found that a high-fat diet can disrupt gut bacteria, alter behavior, and ultimately fuel anxiety through a complex gut-brain connection.

Investigating high-fat diets

The research team, led by Professor Christopher Lowry of integrative physiology, conducted an experiment with adolescent rats to understand the effects of high-fat diets.

The rats were divided into two groups: one group received a standard diet with about 11% fat, while the other group was fed a high-fat diet with 45% fat, primarily from saturated animal fats.

For nine weeks, the researchers monitored the rats’ gut bacteria through fecal samples and assessed their behavior.

Significant findings beyond weight gain

As expected, the rats on high-fat diets gained more weight compared to the control group. However, the study revealed more significant findings beyond weight gain.

The high-fat diet group exhibited significantly less diversity in their gut bacteria, a factor generally linked to poorer health.

They had an increased ratio of Firmicutes to Bacteroidetes, a bacterial imbalance often associated with industrialized diets and obesity.

Gut-brain connection

Further analysis showed that the high-fat diet rats had higher expression of three genes (tph2, htr1a, and slc6a4) involved in serotonin production and signaling, especially in the brainstem region known as the dorsal raphe nucleus (cDRD). This area is associated with stress and anxiety.

Although serotonin is typically known as a “feel-good” brain chemical, certain serotonin neurons can trigger anxiety-like responses when activated. Increased expression of tph2 in the cDRD has been linked to mood disorders and suicide risk in humans.

“To think that just a high-fat diet could alter expression of these genes in the brain is extraordinary,” noted Professor Lowry. “The high-fat group essentially had the molecular signature of a high anxiety state in their brain.”

Lowry suspects that an unhealthy microbiome compromises the gut lining, allowing bacteria to enter the body’s circulation and communicate with the brain via the vagus nerve, a direct pathway from the gastrointestinal tract to the brain.

Evolutionary perspective

“If you think about human evolution, it makes sense,” Lowry said. “We are hard-wired to really notice things that make us sick so we can avoid those things in the future.”

In modern times, this sensitivity might explain why high-fat diets can have such a pronounced impact on our gut health and mental well-being. Essentially, our bodies are still using ancient survival strategies to deal with the challenges of contemporary diets.

The role of healthy fats in diet

Not all fats are detrimental. Healthy fats, such as those found in fish, olive oil, nuts, and seeds, can be anti-inflammatory and beneficial for the brain.

Professor Lowry advises consuming a variety of fruits and vegetables, incorporating fermented foods to support a healthy microbiome, and reducing intake of junk food.

If you indulge in high-fat diets like eating a hamburger, consider adding a slice of avocado, as some research suggests that good fats can mitigate some negative effects.

High-fat diets and mental health

This study highlights the intricate relationship between diet, gut health, and mental well-being. While comfort foods might offer immediate relief, their long-term impact on anxiety and overall health could be substantial.

Adopting a balanced diet with healthy fats and diverse nutrients is crucial for maintaining both physical and mental health.

Consequences of high-fat diet

High-fat diets, particularly those high in unhealthy fats, have been linked to various chronic diseases. Beyond impacting gut health and anxiety, such diets can cause inflammation throughout the body.

Chronic inflammation is a precursor to several conditions, including arthritis, Alzheimer’s disease, and certain cancers.

Research shows that high-fat diets can impair cognitive function. Studies indicate that excessive consumption of unhealthy fats can reduce brain plasticity, which is essential for learning and memory. This impairment can affect cognitive abilities and increase the risk of neurodegenerative diseases.

Additionally, high-fat diets can affect liver health. Consistently consuming high-fat foods can lead to non-alcoholic fatty liver disease (NAFLD), where excess fat builds up in liver cells, potentially leading to liver inflammation and damage.

High-fat diets also influence hormone levels. They may disrupt insulin sensitivity, leading to insulin resistance, a condition that often precedes type 2 diabetes. This disruption can affect other hormones involved in hunger and metabolism, contributing to weight gain and metabolic issues.

The study is published in the journal Biological Research.


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