Eating junk food like a samosa or burger when feeling stressed out can actually elevate anxiety levels, researchers said on Monday.

When under stress, people tend to turn to high-calorie food for solace.

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The study by researchers at University of Colorado at Boulder found that in animals, a high-fat diet disrupts resident gut bacteria, alters behaviour and influences brain chemicals in ways that increase anxiety.

Lead author Christopher Lowry, a professor of integrative physiology at CU Boulder, said that to think that just a high-fat diet could alter expression of these genes in the brain is extraordinary.

“The high-fat group essentially had the molecular signature of a high anxiety state in their brain,” Lowry added in the study published in the journal Biological Research.

Throughout the study, the researchers assessed the animals’ microbiome, or gut bacteria. When compared to the control group, the group eating a high-fat diet gained weight. But the animals also showed significantly less diversity of gut bacteria.

The high-fat diet group also showed higher expression of three genes involved in production and signaling of the neurotransmitter serotonin, which is associated with stress and anxiety.

While serotonin is often called a “feel-good brain chemical,” certain subsets of serotonin neurons can, when activated, prompt anxiety-like responses in animals.

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

“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.”

Not all fats are bad, and healthy fats like those found in fish, olive oil, nuts and seeds can be anti-inflammatory and good for the brain, said researchers.