January 15, 2025

What Is the Gut-Brain Axis and How Does Diet Affect It?

By Rebecca Appleman, RD

People now are more educated about mental health than ever. But there is still so much that the average person doesn’t quite understand. For example, you may have heard that there is a neurotransmitter (brain chemical) called serotonin that plays a role in mood and happiness, and that some mental health issues (depression, anxiety) are related to imbalanced serotonin levels.

But you may not know that a *majority* of the body’s serotonin is found not in the brain, but in the gut. Thus, your gut health can directly or indirectly contribute to your mental health, through a process called the “gut-brain axis.”

How to Understand the Gut-Brain Access

The gut-brain axis (GBA) refers to the complex communication network between the gastrointestinal system (gut) and the brain. This bidirectional system involves biochemical signaling between the central nervous system (CNS) and the enteric nervous system (ENS) within the gut, playing a significant role in regulating digestion, mood, immune responses, and overall health.

Increasing research has highlighted how diet influences this connection, emphasizing the importance of gut health in mental and physical well-being. Some of the links between the gut and the brain include:

• The Nervous System – The vagus nerve, the longest cranial nerve, transmits signals between the gut and brain, influencing mood and digestive processes.
• The Endocrine System – Hormones released from the gut, such as serotonin and cortisol, affect mood, stress levels, and overall brain function.
• The Immune System – Gut-associated lymphoid tissue (GALT) plays a critical role in immune defense and inflammation regulation.
• The Microbiome – The gut houses trillions of bacteria, viruses, and fungi that influence health by producing neurotransmitters, vitamins, and other compounds affecting brain activity.

This connection explains a lot of the crossover between mental health and gut functions. For example, when a person is anxious, they can experience gut problems such as IBS. When a person takes a medication to address depression, they may also experience changes in gut function, because a medication that affects serotonin in the brain will affect it in the gut as well.

These changes are not limited to serotonin, either. Dopamine, gamma-aminobutyric acid (GABA), and other chemicals also originate in the gut. Your gut plays a role in reducing inflammation, which can affect brain function, and, of course, when you feel good in your gut, you’re feeling better in your day to day.

Overall, it’s important to have this understanding that the gut-brain axis is not only about general nutrition or stomach discomfort, but also in the development and severity of mental health symptoms.

How Diet Might affect the Gut-Brain Access

Scientists are still looking at the many ways that the gut could play a role in the development and management of mental health issues. It is also not a one-way pathway – your mental health affects your gut health, and so the management of a person’s mental health may also  be necessary to improve gut health and function as well.

Still, as it stands, there is evidence that points to the idea that a person’s diet directly influences the gut microbiome and, by extension, the gut-brain axis. Nutrient intake, food quality, and dietary patterns can either support or disrupt gut health, impacting brain function and mental health.

The following categories of foods may positively impact a person’s gut health and, by extension, their mental health:

• Fiber Rich Foods and Prebiotics – Prebiotic fibers nourish beneficial gut bacteria, promoting microbiome diversity and balance, reducing inflammation, and possibly increasing serotonin production. Some examples include whole grains, asparagus, bananas, artichokes, and onions.
• Probiotic Foods and Fermented Products – Probiotic foods introduce beneficial live bacteria into the gut, potentially enhancing microbial biodiversity. Examples include Greek Yogurt, kefir, sauerkraut, kimchi, and kombucha. When effective, these foods may improve digestion, reduce stress, and support mood regulation by increasing healthy bacterial populations.
• Omega-3 Fatty Acids – Omega-3 fatty acids have anti-inflammatory properties and support brain health and brain cell function. They may also support the brain in part, via their impact on beneficial gut bacteria. Some foods containing Omega-3 fats include fatty fish, ground flaxseeds, and walnuts, among other foods.
• Polyphenols and Antioxidant Rich Foods – Found in berries, green tea, and really any colorful fruit or vegetable, antioxidants are believed to reduce oxidative stress. They also help prevent inflammation and inflammation related damage.
• Proteins, Especially Tryptophan – protein is highly advantageous for overall health, but specific amino acids like tryptophan are directly linked to serotonin production, which as mentioned, is particularly important in mood regulation.

Of course, it’s possible that some foods may have the opposite effect. Refined sugar in excess is known to reduce microbial diversity, and highly processed foods – including some of the foods above if they’ve been overly processed – may not have the nutrients necessary to promote the gut health or mental health goals that a person is looking to achieve.

Nutritionists and Supporting the Gut-Brain Access

To say that your diet could be solely responsible for your mental health, or that it exclusively could cure a mental health disorder, would be inaccurate. That said, continued research on the gut and the gut-brain axis is demonstrating a meaningful relationship between diet, the gut microbiome and mood regulation.

Smart, healthy eating, is not about removing all of the foods you love from your diet. It’s about creating a program that is designed to give you what you love in ways that are beneficial for your body AND your brain. Working with a nutritionist at Appleman Nutrition can help you ensure that you’re giving your body what it needs to promote better mental and physical health, all while considering your favorite food preferences.

Contact Appleman Nutrition today. We are based in New York City, and proud to support all of NY, CT, and FL.