Study Finds Connection Between High-Fat Diet and Anxiety

When stressed out, many of us turn to junk food for solace.

But a new University of Colorado Boulder research has found that a high-fat diet disrupts resident gut bacteria, alters behaviour and, through a complex pathway connecting the gut to the brain, influences brain chemicals in ways that fuel anxiety.

Stress eating, often characterized by consuming high-fat and sugary foods, can exacerbate anxiety. These comfort foods trigger short-term pleasure but can disrupt the body's natural balance, leading to fluctuations in blood sugar levels and hormone imbalances. Over time, this can negatively impact brain chemistry, increasing the likelihood of anxiety.

“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,” said lead author Christopher Lowry.

In the study, researchers divided adolescent rats into two groups. One group received a standard diet containing approximately 11% fat for nine weeks, while the other group was fed a high-fat diet comprising 45% fat, primarily from saturated animal fats.

Throughout the study, researchers collected faecal samples to assess the animals' gut microbiome. After nine weeks, the rats underwent behavioural tests to evaluate the impact of their diets on anxiety and stress levels.

The results showed that compared to the control group, the rats on the high-fat diet unsurprisingly gained weight. However, they also exhibited significantly less diversity in their gut bacteria, a factor associated with poorer health.

Additionally, the high-fat diet group showed increased expression of three genes involved in the production and signalling of the neurotransmitter serotonin, particularly in a brainstem region linked to stress and anxiety. This reduced bacterial diversity and altered gene expression in the high-fat diet group underscore the potential impact of diet on mental health.

While serotonin is often billed as a “feel-good brain chemical, certain subsets of serotonin neurons can, when activated, prompt anxiety-like responses in animals. Notably, heightened expression of tryptophan hydroxylase has been associated with mood disorders and suicide risk in humans. 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,” said Lowry.

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. Biol Res 57, 23 (2024). https://doi.org/10.1186/s40659-024-00505-1