Does Diet Affect Mental Health?

Our body is made up of multiple organ, tissue, and cell systems that keep us healthy and functioning. Some of these include the cardiovascular system, the central nervous system, the endocrine system, and the digestive system. 

In biology classes, these systems are often presented as completely separate, and there is little focus on how systems interact with one another. What does digestion have to do with the heart anyway?

In reality, however, all of the body’s organs, systems, and cells are interconnected. Recent research has shown how these connections go beyond what we would have ever imagined as little as ten years ago

The connection between the digestive system and the brain is one of the most essential inter-system links, but nutrition and health professionals often fail to observe the connection in their practice. 

When health and nutrition coaches overlook the impact of the digestive system on the brain, they are missing the opportunity to have a potentially positive impact on clients’ mental health through eating patterns and exercise. 

In this article, we will give you an overview of the research behind the connection between the gut and the brain, and we will summarize the main findings of research that shows how diet has a direct impact on mental health. 

Finally, we will look in detail at key nutrients that have an impact on human brain health to help inform your client practice. 

The Gut-Brain Axis: The Connection Between Digestive Health and Mental Health

One of the most important, and often undervalued, connections is that which exists between the digestive system and the brain. 

Researchers have now established that there is a clear communication system between the gut and the brain through what is called the gut-brain axis. 

The study of the gut-brain axis has revealed that there is a vast system of communication between two bodily systems that many people view as separate. In fact, these systems are closely intertwined, as we describe below. 

Parts of the Gut-Brain Axis 

The gut-brain axis is defined as the “bidirectional interactions between the central nervous system, the enteric nervous system, and the gastrointestinal tract.” 

The central nervous system consists of the brain and the spinal cord, and the enteric nervous system includes the neural circuits that control basic functions like blood flow, secretions, mucosal transport, and the modulation of immune and endocrine functions. 

The gastrointestinal tract, or GI tract, is the series of hollow organs that include the mouth, esophagus, stomach, large intestine, small intestine, and anus. 

Other organs that are part of the digestive system and have direct interaction with the GI tract include the liver, the pancreas, and the gallbladder. 

Finally, another essential part of the gut-brain axis is the population of bacteria in the intestine.  

What Does the Gut-Brain Axis Have to Do with Mental Health?

The health of the digestive system can have an impact on the chemicals in our brain, including those that impact mood. It also means that our brain health can impact our gut health. 

In other words, what we eat can affect how we feel, and our mental health can impact our digestive health. 

While this concept may sound like a stretch to some, the relationship between gut and brain health is well-established. This is because the gut releases hormones, neurotransmitters, and immunological factors that send signals to the brain and vice versa. 

In fact, the link between the gut and the brain is so strong that some researchers are now proposing that to treat mental health disorders like anxiety, depression, schizophrenia, and autism, they must be seen as disorders of the microbiota, gut and brain as a whole

Gut Bacteria: The Link Between Digestive and Brain Health?

Researchers have recognized that there is another essential component to the connection between the gut and the brain. While the bacteria in the intestines has traditionally been encompassed in the gut side of the gut-brain axis, the microbiota, or bacteria in the gut, are completely separate microorganisms.

In fact, researchers found that a focus on the microbiota helped researchers understand the link between the gut-brain axis and mental health. Alterations in gut microbiota have been associated with mood and depressive disorders and vice versa. In fact, depending on the composition and population of the gut microbiota, it can help to maintain normal mental processes just as it is involved in mental and neurological diseases. 


Mental health diseases and disorders affect the synthesis of hormones like cortisol, activate molecular patterns associated with danger, and chronically activate stress cascades. These, in turn, modify the production of a number of circulating stem cells, which result in dysbiosis, or a lack of balance in intestinal microbiota.

At the same time, gastrointestinal diseases cause a dysbiosis, affecting the production of short-chain fatty acids, neurotransmitter synthesis, and chemical signaling. These also affect the production and modulation of circulating stem cells, which cause a chemical imbalance in the brain. 

As a result, the concept of the gut-brain axis has been expanded to include the microbiota, or the bacteria that lives within our digestive system. The microbiota-gut-brain axis concept recognizes that the digestive system, the neural networks, and, ultimately, the brain also depend on the presence of bacteria in the intestine for overall health. 


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Food and Mood: The Role of Nutrition in Brain Health 

Researchers have established the connection between gut microbiota and brain health. So, establishing a balance of the “right” bacteria in the gut can improve some of the factors that influence mental health. 

How can we establish a healthy population of microbiota in the gut? One of the ways is through diet. Eating foods that are rich in probiotic bacteria, like fermented foods, and prebiotic substances, like fiber, can help to establish a healthy population of the bacteria that are mainly of the phyla Bacteroidetes and Firmicutes. Gut microbiota play a major role in nutritional status and immune system health by metabolizing some dietary nutrients like fatty acids, glucose, and bile acids and drugs. Gut microbiota also digests fiber and synthesizes vitamins and other bioactive molecules. 

In turn, just like the gut-brain axis is bidirectional, so is the relationship between nutritional status and microbiota population. It is no wonder why having a stomach infection can affect your ability to stay alert, and the reasons why feeling nervous can have you rushing to the bathroom.

Note that mental health is in no way all about nutrition. There are many factors that influence mental health, including:

  • Genetic factors
  • Other conditions and diseases
  • Medications
  • Social determinants like life experience, discrimination, and trauma. These have the biggest influence on mental health. 

A person’s nutritional status and microbiota health may be one factor that can affect your body’s ability to modulate the chemicals and hormones that are released in the body as a result of those other factors. 

Nutritional Psychiatry: Can Mental Health Improve Through Diet?

At this point, as health and nutrition coaches, you might be asking yourself what you can do to integrate the knowledge presented here into your practice. 

Nutritional psychiatrists recommend being sensitive to emerging research that focuses on specific and clear evidence that connects eating patterns to brain function.

Nutritional psychiatry is an emerging field that focuses on the scientific evidence that shows the importance of a well-balanced diet for promoting mental health

However, it is important not to jump to conclusions or overstress the impact a change in diet on its own can have on mental health. 

Here is a summary of the evidence around the impact of diet on mental health: 

    • Mood disorders, cognitive disorders, and stress-induced cognitive vulnerabilities are multicausal, meaning several factors influence the appearance and progression of these diseases and conditions. 
    • Brain structure and function are dependent on having the appropriate nutrients available, including amino acids, proteins, vitamins, and minerals. Thus, food intake and quality over long periods of time can affect brain health. 
    • The diet effects gut hormones, neurotransmitters, and the composition of gut microbiota, which all communicate with the brain along the microbiota-gut-brain axis
    • Despite everything mentioned above, there is a lack of definitive evidence that suggests that specific diets, supplements, or nutrients can prevent or treat mental health diseases. 

The field of nutritional psychiatry focuses specifically on filling evidence gaps that will help shed light on innovative and effective therapeutic approaches to addressing public mental health. 

So, while there is a wide body of evidence that points toward the clear connection between diet, gut health, and brain health, there is limited evidence to help formulate clear recommendations that definitively support mental health through what we eat. 

In other words, no dietary pattern is known to definitively prevent or treat mental health illnesses. 

What does this mean for health and nutrition coaches? You can talk to your clients about the importance of a well-rounded diet that supports digestive health and brain health, but as of yet, there is limited evidence to support health professionals in recommending specific diets or nutrients with the primary goal of supporting mental health.

Key Nutrients That Affect Brain Health 

The human brain is a complex organ that functions as the command center for everything that happens in the body. Logically, that means that the brain is very demanding when it comes to its nutrient needs. 

Here, we review some of the key nutrients our brains need to ensure their overall health. 

Note that this section was not written with the purpose of promoting certain nutrients for supplementation; rather, it is meant to strengthen your understanding of current advancements in nutritional psychiatry. If you want to read more about things you should consider before taking or recommending a supplement, you can read this article

Keep in mind that the specific nutrients we mention below must not overshadow the fact that the strongest evidence points toward how nutritional status as a whole, which is determined by components in the overall diet over long periods of time, can impact brain health. 

Omega-3s and DHA

Omega-3 is a type of fatty acid found mainly in seeds, oils, and seafood. Omega-3 fatty acids have long been known to have an important role in heart and brain health maintenance, including brain neurotransmitter generation and membrane receptor function. 

Docosahexaenoic acid (DHA) is the most abundant Omega-3 fatty acid in cell membranes in the brain. In general, the human body cannot efficiently make DHA with other fatty acids, which is why we must get DHA through what we eat. DHA is found almost exclusively in fish and some algae species, though eggs and animal protein also contain small amounts of DHA. 

DHA is especially important during periods in the lifespan when the brain is growing and developing, especially during gestation and in the first years of life. Additionally, a derivative of DHA (neuroprotectin D-1) may protect the brain against aging, neurodegenerative diseases, and injury, including symptoms that result from mild concussive injuries

Prebiotic and Probiotics

Probiotics aren’t technically nutrients, but they do have an essential role in nutrient absorption and immune health. They are the “stars” of the gut part of the gut-brain axis. 

Probiotics are bacteria that form part of a healthy gut ecosystem. In addition to the benefits for mental health, as mentioned above, they also offer benefits for the immune system and digestive health. They have a key role in synthesizing water-soluble nutrients like thiamine, folate, biotin, riboflavin, and pantothenic acid, and they produce up to half of our vitamin K needs. 

We consume probiotics in food and supplements, and those that survive the digestive process go on to colonize the gut.

Prebiotics are essentially “food” for probiotics. For the most part, prebiotics are fiber and other non-digestible substances that probiotics need to thrive. 

Together, probiotics and prebiotics are critical parts of the gut-brain axis.  

Vitamin D

Vitamin D is a fat-soluble vitamin that is best known for its role in bone health. However, it also has an important role in nerve function and other cells in the nervous system. Researchers have established that elderly people with vitamin D deficiency are more likely to develop dementia, and expectant mothers with deficiencies are more likely to have children with autism, ADHD, and schizophrenia-like disorders. 

While chronic vitamin D deficiency may increase the risk of developing serious mental health disorders, there is limited evidence to show that exceeding vitamin D recommendations has additional benefits to brain health. 

B Vitamins

B vitamins have a variety of roles in the brain, including energy production, DNA/RNA synthesis and repair, and the synthesis of many neurochemicals, among others. Initial evidence demonstrates that vitamin B6 and B12 supplementation may benefit memory performance in women of different ages, and vitamin B12 can improve the cognitive impairment of people with some nutrient deficiencies. 

Vitamin E

Vitamin E is an antioxidant vitamin that can help to neutralize free radicals, including those in the brain. Diets rich in vitamin E may help to reduce cognitive decay in the elderly, and it has the potential to ameliorate cognitive impairment after brain trauma


Copper is a mineral needed in very small quantities, but that is essential for brain function. Copper deficiencies or problems with copper homeostasis are connected with neurodegeneration. In fact, in patients diagnosed with Alzheimer’s disease, cognitive decline is associated with low levels of copper in blood plasma. However, excess copper must be avoided, as it can lead to oxidative stress. 


Iron has an important role in brain development in the first years of life, which is one of the reasons young children must have an iron-rich diet. Because iron continues to have a crucial role in normal neuronal tissue function, iron also has a key role in brain aging; to this point, evidence reveals that while iron-deficient anemia has an impact on cognitive health at any point in life, iron accumulation can lead to neurodegenerative disorders. 

Iron is a good example of why individuals should avoid taking nutrient megadoses without previously consulting with a nutrition specialist. 

Main Takeaways

As a health, wellness, and nutrition coach, it is important to be aware of how lifestyle, like diet, has an impact on a wide range of expressions of health. One of these expressions of health is mental health. Through a progressively deeper understanding of the microbiota-gut-brain axis, researchers and health specialists are aware of how what we eat affects brain health and how cognitive disorders have an impact on gut health. 

Nonetheless, while initial research has revealed a clear connection between the health of our gut and the health of our brain, there is a lack of clear recommendations for health professionals to implement into their practice with the goal of preventing or treating mental health disorders. 

For now, it is sufficient to recommend diets that are rich in complex carbohydrates, vitamins, minerals, fiber, and plant and marine-based oils.

Support your clients in adopting eating patterns that are varied in food choice and rich in nutrients and fiber. 


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