When stressed, we often eat junk food for comfort, but new research from University of Colorado Boulder suggests this can backfire. The study found that a high-fat diet in animals disrupts gut bacteria, changes behavior, and affects brain chemicals, leading to more anxiety.
Everyone knows junk food isn’t healthy and can cause weight gain. But it also affects the brain and can increase anxiety. In a previous study, the team found that rats on a high-fat diet, mainly from saturated fats, showed more brain inflammation and anxiety-like behavior.
While results vary, some human studies show that switching from a high-fat, sugary diet to a healthier one can reduce depression and anxiety.
To explore the fat-anxiety link, Lowry’s team divided male adolescent rats into two groups: a standard diet (11% fat) and a high-fat diet (45% fat, mostly saturated from animal products). The typical American diet is about 36% fat.
The researchers collected fecal samples to analyze the gut bacteria and conducted behavioral tests after nine weeks.
The high-fat diet group gained weight compared to the control group and had less diverse gut bacteria. Less diversity in gut bacteria is linked to poorer health. This group had more Firmicutes and fewer Bacteroidetes, a ratio often seen with unhealthy diets and obesity.
The high-fat group also showed higher activity of three genes (tph2, htr1a, slc6a4) related to serotonin production and signaling in a brain area linked to stress and anxiety. While serotonin is usually seen as a “feel-good” chemical, it can also trigger anxiety-like responses.
Surprisingly, a high-fat diet could change these brain gene expressions. The high-fat group had a brain signature indicating high anxiety.
It is unclear how a disrupted gut changes brain chemicals. Lowry suspects an unhealthy gut lets bacteria enter the body and communicate with the brain via the vagus nerve, a connection from the gut to the brain.
Lowry explains that humans have evolved to notice things that make us sick and avoid them. Not all fats are bad. Healthy fats from fish, olive oil, nuts, and seeds can reduce inflammation and benefit the brain.
Lowry’s research in animals suggests that a high-fat diet, especially with saturated fats, can increase anxiety in the short term and make the brain more prone to it later.
He advises eating various fruits and vegetables, including fermented foods for gut health, and avoiding too much pizza and fries. Add avocado if you eat a hamburger; good fats can help counteract bad ones.
A high-fat diet can increase anxiety by disrupting gut bacteria, which affects brain chemicals through the gut-brain connection. This imbalance can lead to higher stress and anxiety.
Journal reference:
- de Noronha, S.I.S.R., de Moraes, L.A.G., Hassell, J.E. et al. High-fat diet, microbiome-gut-brain axis signaling, and anxiety-like behavior in male rats. Biological Research. DOI: 10.1186/s40659-024-00505-1.