Your gut microbiome — which is the collection of trillions of bacteria, fungi, and other microbes in your gut — is crucial for your well-being, including your mental health. If you or someone you love are dealing with depression, it may be helpful to know that the latest evidence suggests a link between gut health and depression.
For example, recent studies have found a connection between specific gut microbes and depression.
Meanwhile, a review of currently available data has suggested that changing the gut microbiome could be an avenue for reducing symptoms of depression and anxiety.
But how exactly do the bacteria in your gut affect mental health, and can a specific diet help improve mental health issues like depression and anxiety?
Let’s have a look at the research behind the gut-brain connection and how the food you eat could affect your mental health.
The gut-brain connection
Your brain and gut are linked by a two-way communication system called the gut-brain axis.
The gastrointestinal tract is not just a long tube through which food is digested. It has its own complex nervous system called the enteric nervous system (ENS), which explains why we refer to the gut as our “second brain.”
The gut-brain axis connects the ENS and central nervous system (CNS), allowing your gut to communicate with the brain, and vice versa.
But how do these two organs communicate? Research suggests the gut microbiome may affect the brain in three main ways:
Vagus nerve pathway: Chemicals produced by gut bacteria can send signals to your brain through the vagus nerve, which runs from your colon to your brain.
Neuroendocrine pathway: Some gut bacteria produce an amino acid called tryptophan, an important building block for neurotransmitters like serotonin, which influence mood.
Immunoregulatory pathway: Gut bacteria interact with your body’s immune system by communicating with immune cells.
Does gut health affect depression?
There’s more and more evidence suggesting that gut health may have a role in managing and even preventing mental health issues like depression.
Research shows that people with depression have different gut microbes from people without depression.
A 2019 observational study found that people with depression had depleted levels of Coprococcus and Dialister, compared with people who reported a higher quality of life. Those with depression also had bacteria associated with Crohn’s disease.
A separate study found lower levels of the bacteria Bifidobacterium and Lactobacillus in people with depression, compared with those without.
To investigate the influence of the gut microbiome on depression, researchers have also looked into whether fecal microbiota transplants (FMT) can affect mental health.
One systematic review looking at the effect of FMT on symptoms of mental health conditions — like depression — observed that FMT from donors without a mental health condition to someone living with a mental health condition relieved symptoms.
Meanwhile, FMT from donors with mental health conditions to those without could induce symptoms.
Experts are still trying to figure out how the gut microbiome affects depression, but one main theory involves serotonin.
Serotonin is a neurotransmitter — a chemical messenger — that helps regulate mood and promotes feelings of happiness. Research shows the gut microbiome can influence levels of serotonin, which scientists have long linked to depression.
However, a possible link between the gut microbiome and serotonin production would only be part of the puzzle. More so, experts have recently started to reevaluate the role serotonin plays in depression.
Can changing your diet help with depression?
There’s growing evidence that our diet could have a crucial effect on our mental health, thanks to its effect on the gut microbiome — a field of research known as psychobiotics.
Following specific diets could even reduce the risk of developing depression. A 2018 systematic review concluded that people who followed the Mediterranean diet had a 33% lower risk of depression than people who did not.
A separate study examined whether diet could improve symptoms of depression. The SMILES trial was a 12-week randomized control trial of people with major depressive disorder.
These study participants were split into two groups and randomly assigned either personalized nutritional consulting sessions or social support counseling.
At the end of the study, 32% of the diet group were considered to be in remission from depression, compared with just 8% in the counseling group. The trial also found that the more the participants improved their diet, the more their depression improved.
Those in the diet group increased their consumption of fruits and vegetables, whole grains, nuts and seeds, fish, and healthy fats while reducing their intake of processed foods — dietary patterns in line with the Mediterranean diet.
Although this was another small-scale study — and some of the participants in each group were taking antidepressants throughout the study — the results are promising.
They provide a valuable jumping-off point for evidence on how diet can help with depression and the role of the gut-brain axis.
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Meanwhile, a 2017 paper published in the journal Nutritional Neuroscience outlined five dietary recommendations to prevent depression based on current evidence:
following “traditional” dietary patterns like the Mediterranean, Norwegian, or Japanese diets
increasing your intake of fruits, vegetables, legumes, wholegrain cereals, nuts, and seeds
increasing your intake of foods rich in omega-3 polyunsaturated fatty acids
replacing unhealthy foods with wholesome nutritious foods
limiting your intake of processed foods, fast food, commercially baked goods, and sweets
The study authors stressed that these recommendations aren’t set in stone and could change if the scientific evidence evolves.
At ZOE, we know that everyone’s gut microbiome and responses to particular foods are different.
ZOE scientists and their colleagues, who run the largest nutritional study of its kind, recently identified 15 “good” gut bugs that are linked to good health. They also found 15 “bad” bugs that are indicators of poor health.
Take our free quiz to learn how you can discover which of the 15 good and bad bugs live in your gut, as well as your personal “gut boosters” and “gut suppressors,” so you can eat more of the right foods for your unique microbiome.
'Leaky gut syndrome' and depression
A gastrointestinal disorder called “leaky gut syndrome” has been gaining more and more notoriety, and some people have linked it to depression, but it’s important to note that there is little evidence for this link.
Leaky gut syndrome is a phenomenon where toxins and bacteria supposedly “leak” through the intestinal lining into the bloodstream, causing the onset of unpleasant symptoms like bloating, cramping, and mood swings.
The lining of your intestine is made of tightly packed junctions that control what is absorbed into the intestine, acting as a physical barrier to prevent any unwanted substances from entering the bloodstream.
A small level of gut permeability is considered normal, but in some people — like those with Crohn's and celiac disease — this protective barrier is compromised, known as increased intestinal permeability.
Proponents of leaky gut syndrome believe it’s the underlying cause of all sorts of conditions, including everything from migraines and psoriasis to food sensitivities, fibromyalgia, multiple sclerosis, autism, and even depression.
Most of these claims haven’t been proven, and mainstream medicine doesn’t recognize leaky gut syndrome as a real diagnosis.
There isn’t any real evidence to suggest leaky gut syndrome is the cause of disease, but rather experts think increased gut permeability could be a symptom of some illnesses.
So, where did the link between leaky gut syndrome and depression come from? One very small preliminary study found biomarkers of gut permeability in patients with a history of suicidal behavior or depression.
The study authors concluded that leaky gut syndrome could explain the role of inflammation in depression or suicidal behavior, but they couldn’t find any definite causal link.
The study had several limitations. Aside from a very small sample size, the researchers even concluded that their results were probably affected by variables like smoking, alcohol intake, and dietary habits — all of which can affect your gut health.
Until more research is done on the role of gut permeability in disease, we can’t confidently say that leaky gut syndrome is a valid condition, nor that it’s linked to depression.
Although the scientific evidence is still young, existing research on gut health and depression shows there’s a link between your gut bacteria, what you eat, and your mental health.
What we know so far about the gut-brain axis could help support the theory that following a diet that supports gut health could be helpful in managing and preventing depression.
A diet rich in fruits, vegetables, whole grains, and healthy fats could reduce the risk of depression, but the research is still emerging.
There still isn’t enough evidence to prove a causal link between the gut microbiome and depression, so we should be cautious about using food as the only treatment tool for the condition.
If you’d like to learn more about how to eat the right foods for your unique gut microbiome, check out ZOE’s at-home testing kit.
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Leaky gut biomarkers in depression and suicidal behavior. (2018).
Neurotransmitter modulation by the gut microbiota. (2019).
Possible association of Bifidobacterium and Lactobacillus in the gut microbiota of patients with major depressive disorder. Journal of affective disorders. (2016).
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The Gut-Brain Axis: The Missing Link in Depression. (2015).
The neuroactive potential of the human gut microbiota in quality of life and depression. (2019).
Vagus Nerve as Modulator of the Brain–Gut Axis in Psychiatric and Inflammatory Disorders. (2018).
What has serotonin to do with depression? (2015).