When we’re stressed, many of us reach for junk food for comfort.
However, new research from CU Boulder suggests that this habit might make us more anxious instead of helping us feel better.
The study found that in animals, a high-fat diet disrupts gut bacteria, changes behavior, and affects brain chemicals in ways that increase anxiety.
“Everyone knows that junk food is unhealthy, but we usually think it only leads to weight gain,” said lead author Christopher Lowry, a professor of integrative physiology at CU Boulder.
“If you realize it also affects your brain and can cause anxiety, the risks become even more serious.”
In this study, published in the journal Biological Research, Lowry collaborated with Sylvana Rendeiro de Noronha, a doctoral student at the Federal University of Ouro Preto in Brazil.
They previously found that rats fed a high-fat diet showed more brain inflammation and anxiety-like behavior.
To explore this further, the researchers divided male adolescent rats into two groups. One group received a standard diet with about 11% fat, while the other group got a high-fat diet with 45% fat, mostly from saturated animal fats.
This high-fat diet is similar to the typical American diet, which is about 36% fat according to the Centers for Disease Control and Prevention (CDC).
After nine weeks, the researchers collected fecal samples and studied the animals’ gut bacteria. They also performed behavioral tests on the rats. Unsurprisingly, the high-fat diet group gained more weight.
However, these rats also had less diversity in their gut bacteria, which is generally linked to poorer health.
They had more Firmicutes bacteria and fewer Bacteroidetes bacteria, a balance often associated with obesity and unhealthy diets.
The high-fat diet rats also showed higher levels of three genes (tph2, htr1a, and slc6a4) involved in serotonin production and signaling.
Serotonin is a brain chemical often thought to make us feel good, but some types of serotonin neurons can actually increase anxiety. Higher levels of the gene tph2 in the brain have been linked to mood disorders and suicide risk in humans.
“The fact that a high-fat diet can change these brain genes is extraordinary,” said Lowry. “The high-fat diet rats had brain changes that made them more anxious.”
Gut-Brain Connection
It’s not entirely clear how changes in the gut affect the brain, but Lowry thinks an unhealthy gut microbiome might damage the gut lining. This allows bacteria to enter the body and communicate with the brain through the vagus nerve, which connects the gut and brain.
“In human evolution, it makes sense. We are programmed to notice things that make us sick so we can avoid them in the future,” Lowry explained.
Lowry emphasizes that not all fats are bad. Healthy fats found in fish, olive oil, nuts, and seeds are good for the brain and can reduce inflammation. However, his research suggests that eating too much saturated fat, especially at a young age, can increase anxiety in the short term and make the brain more prone to anxiety in the future.
His advice: Eat a variety of fruits and vegetables, include fermented foods to support gut health, and avoid too much junk food. If you do have a hamburger, add some avocado. Good fats can help counteract some of the negative effects of bad fats.
If you care about nutrition, please read studies about how Mediterranean diet could protect your brain health, and the best time to take vitamins to prevent heart disease.
For more information about nutrition, please see recent studies that olive oil may help you live longer, and vitamin D could help lower the risk of autoimmune diseases.
