During stressful periods, it’s common to instinctively reach for high-fat foods like fried chicken, potato chips, or ice cream. However, recent research reveals that consuming fatty foods might actually worsen anxiety due to the connection between gut bacteria and brain chemicals that regulate anxiety levels. These findings emphasize the need to rethink dietary choices beyond just weight management concerns.
The study, conducted at the University of Colorado Boulder and published in the journal Biological Research, examined how a high-saturated-fat diet impacts gut bacteria, behavior, and brain chemistry in rats.
Saturated fats, primarily found in animal products and tropical oils (such as fatty meat, processed meat products like bacon and salami, cheese, cream, butter, coconut oil, palm oil, ice cream, ghee, lard, biscuits, pastries, cakes, and pies), have been shown to disrupt mitochondrial function in the gut when consumed in high amounts.
Professor Christopher Lowry, the lead author and professor of integrative physiology at UC Boulder, noted, “Everyone knows that these are not healthy foods, but we tend to think about them strictly in terms of a little weight gain. If you understand that they also impact your brain in a way that can promote anxiety, that makes the stakes even higher.”
The research team collected fecal samples and assessed the animals’ microbiomes to determine the diet’s effects on their behavior. After nine weeks, the animals on a high-fat diet gained weight compared to the control group and displayed significantly reduced gut bacteria diversity, resembling the typical industrialized diet and obesity. Less diversity in gut bacteria generally correlates with poor health.
In the high-fat diet group, researchers observed increased expression levels of three genes involved in the production and signaling of serotonin, a neurotransmitter. This was especially evident in a region of the brain stem associated with stress and anxiety. While serotonin is commonly known as a “feel-good” brain chemical, certain subsets of serotonin neurons can trigger anxiety-like responses when activated. One of the three genes with elevated expression in the brain stem region linked to stress and anxiety is also associated with mood disorders and a higher risk of suicide in humans.
“To think that just a high-fat diet could alter expression of these genes in the brain is extraordinary,” said Professor Lowry. “The high-fat group essentially had the molecular signature of a high anxiety state in their brain.”
Professor Lowry believes that high-fat diets may contribute to anxiety by disrupting the microbiome, leading to a compromised gut lining. This weakened barrier can allow bacteria to enter the bloodstream and interact with the brain via the vagus nerve, a crucial pathway connecting the gastrointestinal tract to the brain.
Despite recommendations that saturated fat intake should not exceed 11% of energy intake from food—20g per day for women and 30g per day for men—the average American diet consists of about 36% fat, according to the Centers for Disease Control. This excess fat intake may not only contribute to weight gain but also potentially worsen anxiety, as suggested by the study’s findings.
In an earlier study, the UC Boulder research team discovered that rats consuming a high-fat diet, predominantly made up of saturated fats, exhibited increased neuro-inflammation and anxiety-like behaviors.
A 2019 study showed that replacing a diet high in saturated fats, sugars, and ultra-processed foods with a healthier diet can reduce depression and anxiety.
Healthy fats, such as those found in fish, certain oils, nuts, and seeds, can be anti-inflammatory and beneficial for the brain. Examples include rapeseed oil, olive oil, avocados, Brazil nuts, flax seeds, mackerel, and salmon.
Lowry’s advice: Eat as many different kinds of fruits and vegetables as possible, add fermented foods to your diet to support a healthy microbiome, and stay away from ultra-processed and fast foods. Also, if you do have bad fat, like a hamburger, add a slice of avocado. Research shows that good fat can counteract some of the bad.
“If you think about human evolution, it makes sense,” he said. “We are hard-wired to really notice things that make us sick so we can avoid those things in the future.”
