When feeling stressed, many of us may turn to junk food for comfort. Perhaps some chocolate for a mid-afternoon boost, or a donut on the way home to reward surviving another 9 to 5. However, scientists at the University of Colorado Boulder have discovered that eating fatty foods may actually make our anxiety worse. Which, let’s face it, isn’t ideal.
The team found that when animals were given a high-fat diet, it disrupted their gut bacteria – which in turn altered the brain chemicals that fuel anxiety.
High-Fat Diets Disrupt Gut Bacteria and Increase Anxiety in Rats
The study, published in the journal Biological Research in May, revealed that a high-fat diet (HFD) can significantly impact gut bacteria and increase anxiety levels in animals. The research, conducted on male Wistar rats over nine weeks, provides new insights into how dietary choices affect mental health through the gut-brain axis.
In scientific terms, here’s what the researchers found:
Key Findings
Altered Gut Microbiome: Rats fed with a high-fat diet showed decreased diversity and altered community composition of gut bacteria compared to those on a control diet. Specifically, the HFD increased the Firmicutes/Bacteroidetes ratio, with higher abundances of Blautia and lower levels of Prevotella.
Increased Anxiety: The rats on the HFD exhibited more anxiety-related behaviors. These behaviors were assessed using the elevated plus-maze (EPM), light/dark box (LDB), and open-field (OF) tests, with significant increases in anxiety-related defensive behaviors noted in the EPM.
Gut-Brain Connection: The study highlighted the role of the microbiome-gut-brain axis in these behavioral changes. HFD-fed rats showed increased expression of serotonergic genes (tph2, htr1a, and slc6a4) in the brainstem, particularly in the dorsal raphe nucleus, a region associated with stress and anxiety responses.
Lead author Professor Christopher Lowry explained: “Everyone knows that these [high-fat items] 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.”
What Does This Mean in Simple Terms?
Imagine your gut is like a garden. A variety of plants (or bacteria) living there keep it healthy and balanced. When you eat a lot of fatty foods, it’s like pouring chemicals on the garden that kill off some plants and make others overgrow. This messes up the balance and can cause problems.
Now, think of your brain as a control center that talks to this garden through a special phone line (the gut-brain axis). When the garden is out of balance, the messages sent to your brain get scrambled, making you feel more anxious.
The Dark Side of Serotonin
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 tph2, or tryptophan hydroxylase, in the caudal part of the dorsal raphe nucleus (cDRD) has been associated with mood disorders and suicide risk in humans. This study found that rats on a high-fat diet had increased expression of these genes, indicating a high anxiety state in their brains.
A Primal Gut-Brain Connection
The study suggests that an unhealthy microbiome may compromise 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.”
Implications for Mental Health
These findings underscore the importance of diet on mental health. While the study was conducted on rats, the mechanisms identified may also be relevant to humans. This research adds to the growing body of evidence that supports maintaining a balanced diet for overall well-being, including mental health.
Practical Advice for a Healthier Mind and Body
Lowry advises eating a variety of fruits and vegetables, adding fermented foods to support a healthy microbiome, and avoiding ultra-processed, high-fat foods. Not all fats are bad, and some research shows good fats, such as those from avocados, can counteract the bad fats from foods like burgers. In addition, healthy fats found in fish, olive oil, nuts, and seeds can be anti-inflammatory and beneficial for the brain.
What This Means for You
Understanding that high-fat diets can affect not just your weight but also your brain and mental health can be a powerful motivator for making healthier food choices. A diet high in saturated fats can lead to an unhealthy gut microbiome, which in turn can increase anxiety and stress levels. By focusing on a diet rich in diverse, nutrient-dense foods, you can support your gut health and, consequently, your mental well-being.
Conclusion
The study provides compelling evidence that high-fat diets can disrupt gut bacteria and increase anxiety through complex gut-brain interactions. It highlights the need for further research to explore the potential for dietary interventions in managing anxiety and other mental health disorders.
For those interested in the intricate relationship between diet, gut health, and mental well-being, this study serves as a crucial reminder of the impact of our food choices on our overall health.
The researchers concluded that “this knowledge could lead to new microbiome-based approaches to prevent stress-related psychiatric disorders such as anxiety disorders.”
Citation:
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
