Introduction

Researchers and medical experts have become increasingly focused on how gut bacteria can potentially impact mental health. The gut-brain axis is the communication network that connects the gut and brain. These two organs are linked physically and biochemically in several ways.  

What you eat directly affects the structure and function of your brain and, ultimately, your mood. Many people do not realize how strong an impact their gut has on mood. Your brain requires a constant supply of fuel, which comes from the foods you eat. The community of microorganisms, such as bacteria, that live in your digestive tract is called the microbiome.  

How the Gut and Brain Communicate

Your gut and brain are constantly communicating through the nervous system, neurotransmitters, and the immune system.  

The nervous system

Your gut contains around 168 million nerve cells, called neurons, that are connected to your brain. The vagus nerve is one of the biggest nerves connecting the gut and brain, sending signals in both directions.  

Neurotransmitters

Your gut and brain are also connected through chemicals called neurotransmitters. Many of these are produced in the gut and have a significant impact on mood. Two significant neurotransmitters are serotonin and gamma-aminobutyric acid (GABA).  

• Serotonin: About 95% of your body's serotonin, a neurotransmitter that helps regulate sleep, appetite, and mood, is produced in your gastrointestinal tract; 

• Gamma-aminobutyric acid (GABA): Gut microbes produce GABA, which helps control feelings of fear and anxiety.  

Gut Microbes and Diet

The trillions of microbes in your gut produce chemicals that can affect the brain. When you digest fiber, gut microbes produce short-chain fatty acids (SCFAs). These SCFAs, like butyrate, are important for the blood-brain barrier and can influence brain function.  

Inflammation

The gut-brain axis is also connected through the immune system. The gut and its microbes play a key role in inflammation by controlling what enters the body. If the gut barrier becomes ‘leaky’, it can allow inflammatory toxins made by bacteria, such as lipopolysaccharide (LPS), to pass into the blood. This chronic, low-grade inflammation has been identified as a potential factor in mental health deterioration and is associated with brain disorders like depression.  

The Role of Diet in Gut and Mood Health

Research shows a strong connection between diet, inflammation, and mental health.  

Inflammatory Diets

Diets with pro-inflammatory characteristics are strongly linked to an increased risk of developing depression and anxiety. Multiple studies have found a correlation between diets high in refined sugars and processed foods and impaired brain function or a worsening of mood disorder symptoms.  

Anti-inflammatory diets

An anti-inflammatory diet, rich in vegetables, fruits, unprocessed grains, and fish, may offer a protective approach against these mental health issues. Studies have shown that the risk of depression is 25% to 35% lower in people who eat traditional diets, like the Mediterranean or traditional Japanese diets, compared to a typical ‘Western’ diet.  

These traditional dietary patterns regularly incorporate many of the gut-supporting foods listed below, such as whole grains, fruits, vegetables, and fish. 

Foods that Support the Gut-brain Axis

Changing your gut bacteria by eating certain foods may improve your brain health. These food types are examined below. 

Probiotic Foods

Probiotics are live, beneficial bacteria found in yogurt, kefir, sauerkraut, and other fermented foods. Probiotics that affect the brain are sometimes called ‘psychobiotics’. Some have been shown to improve symptoms of stress, anxiety, and depression. Kefir is a fermented milk drink that contains various helpful bacteria and yeasts. It has many health benefits, including antimicrobial and anti-inflammatory properties, and it helps modulate the gut microbiota.  

Prebiotic Foods

Prebiotics are food components, typically fibers, that feed the ‘good’ bacteria in your gut. They are found in high-fiber foods such as whole grains, nuts, seeds, fruits, and vegetables. Pulses—a food group including beans, lentils, and chickpeas—are particularly rich in fiber. Other great prebiotic sources include apples, asparagus, bananas, garlic, and onions.  

Omega-3 Fatty Acids

Found in oily fish, omega-3 fatty acids are essential for brain health. Studies show that omega-3s can increase good bacteria in the gut and reduce the risk of brain disorders.  

Polyphenol-rich Foods  

Cocoa, green tea, olive oil, and coffee contain polyphenols, which are plant chemicals digested by your gut bacteria. Polyphenols can increase healthy gut bacteria and may improve cognition.  

Tryptophan-rich Foods

Tryptophan is an amino acid that gets converted into the neurotransmitter serotonin. Foods high in tryptophan include turkey, eggs, and cheese. 

Signs of an Unhealthy Gut

When your body lacks enough good bacteria, bad bacteria can thrive, leading to an imbalance. According to Georgia family physician Diondra Atoyebi, this imbalance can lead to several issues:  

• Digestive issues, such as irritable bowel syndrome (IBS), constipation, diarrhea, and heartburn; 

• Autoimmune problems; 

• Sleep issues; 

• Skin rashes and allergies;  

• Mood changes, including increased fatigue, depression, and anxiety.  

Important Considerations 

To practically incorporate these excellent foods into your overall dietary pattern, consider following guidelines like MyPlate or adopting healthy eating patterns such as the Mediterranean diet.  

The Mediterranean diet, for example, emphasizes vegetables, fruits, whole grains, legumes, nuts, seeds, olive oil, and fish, all of which are rich in prebiotics, polyphenols, omega-3s, and other beneficial compounds.  

While specific serving recommendations for mood benefits are still emerging, aiming for a diverse intake of these food groups regularly as part of a balanced diet is a good approach.

Probiotic Safety

Probiotic supplements contain select, beneficial types of microbes to add to the populations already living in your body. Many are oral supplements.  

Probiotics have a long history of safe use, especially in healthy people. However, the risk of harmful effects is greater for people with severe illnesses or compromised immune systems. The United States Food and Drug Administration (FDA) has warned health care providers about the risk of severe or fatal infections in premature infants given probiotics.  

When considering probiotic supplements, look for products that are third-party tested by organizations such as NSF International or USP, as this can help ensure quality, purity, and that the product contains what it claims. Always consult with a healthcare provider before starting any new supplement, especially if you have underlying health conditions. 

When to See a Doctor

Talk to your doctor if you have symptoms of poor gut health. Don't use probiotics or dietary changes as a reason to postpone seeing a health care provider about a health problem. It is important to discuss any complementary health approaches, including dietary supplements, with your provider. 

Resources

Farag, M. A., Jomaa, S. A., Abd El-Wahed, A., & El-Seedi, H. R. (2020). The Many Faces of Kefir Fermented Dairy Products: Quality Characteristics, Flavour Chemistry, Nutritional Value, Health Benefits, and Safety. Nutrients, 12(2), 346. 

Ferreira, H., Vasconcelos, M., Gil, A. M., & Pinto, E. (2020). Benefits of pulse consumption on metabolism and health: A systematic review of randomized controlled trials. Critical Reviews in Food Science and Nutrition, 61(1), 85-96. 

National Center for Complementary and Integrative Health. (2019, August). Probiotics: Usefulness and Safety. U.S. Department of Health and Human Services, National Institutes of Health. 

Pang, C., Yu, H., Xie, J., Chen, Y., Cao, W., Yu, X., Zhu, L., Zhang, J., Gao, L., Li, Y., Du, L., Deng, B., & Ji, L. (2025). Pro-inflammatory diet and the risk of depression and anxiety: A prospective study based on the dietary inflammatory index. Journal of Affective Disorders, 387, 119533. 

Piedmont Healthcare. (n.d.). Family Physician Shares Signs of Poor Gut Health. 

Robertson, R. (2025, March 6). The Gut-Brain Connection: How it Works and The Role of Nutrition. Healthline. 

Selhub, E. (2022, September 18). Nutritional psychiatry: Your brain on food. Harvard Health Publishing. 

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