How a high-fat diet can cause anxiety | CU Boulder Today

When we feel stressed, many of us turn to junk food for comfort, but a new study from the University of Colorado Boulder suggests this strategy can backfire.

Research has found that in animals, a high-fat diet disrupts gut bacteria, alters behavior and affects brain chemistry in anxiety-inducing ways via complex pathways connecting the gut and the brain.

“We all know these are not healthy foods, but we tend to think of them only in terms of making us gain a little weight,” said Christopher Rowley, a professor of integrative physiology at the University of Colorado Boulder and lead author of the study. “When you understand that they also affect the brain and may contribute to anxiety, the danger becomes even more pronounced.”

About the research published in the journal Biological Research In May, Rowley collaborated with first author Silvana Rendeiro de Noronha, a doctoral student at the Federal University of Ouro Preto in Brazil.

In a previous study, the team found that rats fed a high-fat diet consisting mainly of saturated fats showed increased neuroinflammation and anxiety-like behavior.

The evidence is mixed, but some human studies Also show Replacing high-fat, high-sugar, ultra-processed foods with healthier alternatives may help reduce depression and anxiety.

The dark side of serotonin

To better understand the causes of the link between obesity and anxiety, Rowley's team split adolescent male rats into two groups: Half were fed a standard diet containing about 11 percent fat for nine weeks, while the other half were fed a high-fat diet containing 45 percent fat, mostly saturated fat from animal sources.

According to the Centers for Disease Control and Prevention, the typical American diet contains about 36 percent fat.

During the study, the researchers collected fecal samples and assessed the animals' microbiomes, or gut bacteria. After nine weeks, the animals underwent behavioral tests.

Compared to the control group, the group that ate the high-fat diet unsurprisingly gained weight. But the diversity of the animals' gut bacteria was also significantly reduced. In general, the more diverse the bacteria, the better the health, explained Rowley. The animals' gut bacteria also had far more of a group of bacteria called Firmicutes and less of a group called Bacteroides. A higher ratio of Firmicutes to Bacteroides is associated with a typical industrialized diet and obesity.

The expression of three genes was also higher in the high-fat diet group (tph2, htr1a, and slc6a4) is involved in the production and signaling of the neurotransmitter serotonin, particularly in an area of ​​the brainstem called the dorsal raphe nucleus (cDRD), which is associated with stress and anxiety.

Serotonin is well known as the “feel good brain chemical,” but Rowley points out that when a specific subset of serotonin neurons is activated, it can trigger anxiety-like responses in animals. tph2Tryptophan hydroxylase defects in cDRD have been associated with mood disorders and suicide risk in humans.

“It's surprising to think that just a high-fat diet would change the expression of these genes in the brain,” Rowley says. “The high-fat group's brains essentially had the molecular signature of a heightened state of anxiety.”

The primitive connection between the gut and the brain

It's still unclear how gut disorders change brain chemistry, but Rowley thinks that an unhealthy microbiome may weaken the intestinal lining, allowing bacteria to enter the circulation and communicate with the brain via the vagus nerve, which leads from the digestive tract to the brain.

“If you think about human evolution, it makes sense,” Rowley says, “that we're hardwired to really notice things that make us sick, so we can avoid them in the future.”

Lawley stresses that not all fats are bad, and healthy fats such as those found in fish, olive oil, nuts and seeds are anti-inflammatory and good for the brain.

But his research in animals suggests that exposure to a very high-fat diet consisting mostly of saturated fats, especially at a young age, can increase anxiety in the short term and predispose the brain to anxiety in the future.

His advice: eat as many different kinds of fruits and vegetables as possible, add fermented foods to your diet to support a healthy microbiome, avoid pizza and fries, and if you do eat a burger, add a slice of avocado. Research suggests Good fats can counteract some of the bad fats.

Rodrigo Cunha de Menezes, a professor of physiology at the Federal University of Ouro Preto in Brazil, is co-lead author of the paper.