The gut is an organ far away from the brain, but they are interconnected in different ways. Still, it might be difficult to think that something in your gut alters how your brain works.
So many things influence stress, anxiety, depression, and other psychological symptoms. The environment, what you’re going through, and your genetic predisposition play a role. But what you eat and how your gastrointestinal system works may also contribute to the process.
Recent medical findings revealed the activity of the gut and the gut microbiota. Researchers have shown repeatedly that gut bacteria have far-reaching implications for our health. They can influence how the immune system works. They have endocrine functions and synthesize a few vitamins. They also have anti-inflammatory potential. And there’s something called the brain-gut axis, which is captivating the attention of current medical research.
What is it about? How can microbes change the way our brain works? Can we take probiotics to improve mood disorders? In this article, we’re answering these questions and more.
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The concept of psychobiotics is becoming popular to describe microbes with mood-altering potential. In a recent review published in the journal Biological Psychiatry, the term psychobiotic was applied to a live organism that improves patients with psychiatric disorders. What they do is creating substances that stimulate nerves in the gut and modulate nervous function. These substances can be serotonin, aminobutyric acid, and many others.
As such, they have the potential to become an alternative solution for anxiety and depression. Even patients with chronic fatigue syndrome may benefit from this type of live organism in the gut. If you don’t have any psychiatric problem, these microorganisms may contribute to stabilize your mood and protect you from these problems in the long term (1).
The association between the gut and brain function is not something new. For many years, we knew that serotonin was one of the most critical neurotransmitters in the brain. What’s more, one of the most successful antidepressant medications is known as a selective serotonin reuptake inhibitor.
It reduces the rate of the reuptake of serotonin, allowing the neurotransmitter to stimulate cells for a longer time. But for many years, it is also known that the gut produces much more serotonin than the brain. It is only localized in another area, but it is precisely the same molecule.
Serotonin in the gut is useful to promote bowel movements. However, it also stimulates nerve terminals that take the signal up to the brain. The pathway is still unknown, and there are many questions left to answer. Still, the fact remains that many patients with depression improve with serotonin-producing probiotics, and this is one likely reason.
Other neurotransmitters produced in the gut include the inhibitor GABA (gamma-aminobutyric acid), acetylcholine, and catecholamines. When they contact the gut lining and nerve terminals, they trigger signals to the brain and modulate our behavior (2).
Besides triggering nerve impulses through newly-synthesized neurotransmitters, these probiotics have additional pathways. Other researchers described effects in the stress response system and the regulation of stress hormones. This happens through the hypothalamic-pituitary-adrenal axis or HPA axis. When regulated, the HPA axis releases cortisol in the morning and stops releasing this hormone at night. Timing of cortisol release is fundamental to wake up every day, sleep properly, stay alert, and maintain proper immune function. When it becomes disrupted, the sleep pattern turns south, and we become moody and very anxious. By regulating the HPA axis, these bacteria act on the brain and solve cognitive problems and mood disorders (3).
We can also name another pathway through inflammatory substances. Brain inflammation triggers mood problems when it is sustained for a long time. There is something called systemic inflammation. Unlike localized gut inflammation, this type is not as severe, but it is prolonged and has long-term consequences. One of them is triggering depression, mood problems, and neurodegenerative diseases.
Many healthy bacteria have anti-inflammatory properties. They synthesize lipid metabolites called short-chain fatty acids. These fatty acids work similarly to hormones in the gastrointestinal system and the rest of the body. They have many functions, but one of them is acting as anti-inflammatories. Healthy microbiota uses this and other pathways to lower inflammation. By controlling systemic inflammation, mood problems can also improve significantly (4).
Each probiotic bacteria has different functions and contributes to your mood in different ways. Which ones are recommended to uplift your mood? Well, there is no current protocol because the answer to that question is under research. However, most scientific studies consider one of these strains or a combination:
- Lactobacillus spp, especially Lactobacillus casei, Lactobacillus Plantarum, Lactobacillus helveticus, Lactobacillus rhamnosis, and Lactobacillus acidophilus.
- Bifidobacterium spp, especially Bifidobacterium bifidum and Bifidobacterium longum
The link between your gut and health
As noted above, the gut and the brain are distant organs, but they are connected differently. This is how the signals by your gut microbiome reach the brain:
- Through a complex network of sensory nerves: The gut is often called the second brain because there’s a complex network of nerves in this area. It is called the enteric nervous system. It has sensory nerves and sends impulses to the brain. Most of them have a purely organic function. Others deal with specialized brain centers and have multiple connections all over the brain. They all travel through the vagus nerve. That is why sometimes depression can trigger diarrhea, and the link is particularly evident in patients with irritable bowel syndrome. The link may also run in the opposite direction, but the pathways and exact reasons are not yet understood.
- Through hormones and other substances: Our cells are very far from each other, but they are connected by substances that run in the blood vessels. They are hormones and act as a signal to synchronize every cell of the body with the rest. Hormones and the gut are deeply related to each other. Anxiety may trigger diarrhea, and substances from the gut reach the brain and provide relief.
- Through modulation of the immune system: In the gut, a network of lymph nodes is called GALT. It stands for Gut-Associated Lymphoid Tissue. GALT is a complex network of immune tissue in close contact with gut microbes. Any change of healthy microbes in your colon makes a difference in GALT, activating or inhibiting inflammation. Through anti-inflammatory substances, your healthy microbes combat degeneration in several tissues, including the brain.
What does science say?
It all looks fantastic on the drawing board, but is it really applicable? To answer that question, clinical trials are required. There are different types of clinical trials, and they need to be held one after the other to finally translate the findings into treatment protocols.
The first research is done in animal models. When safety and efficacy are proven in animal models, the next step is trying in humans. First, in very small groups that will gradually increase in size.
This is the usual process new drugs take to develop, and the same happens with probiotics. So far, the research is still in the early stages, and there is no final word about its efficacy. But according to science, there are two main applications of probiotics for mental health:
- Probiotic applications for anxiety and depression
- Probiotic applications for stress
Probiotics research for anxiety and depression
There is a lot of research about probiotics for anxiety and depression. The most common probiotic strains for anxiety and depression are:
- Lactobacillus casei
- Lactobacillus acidophilus
- Lactobacillus helveticus
- Lactobacillus Plantarum
- Bifidobacterium bifidum
- Bifidobacterium longum
- Bifidobacterium breve
One clinical trial to relieve depression used 2 billion colony forming units (CFUs) of L. acidophilus, L. casei, and B. bifidum. This was administered in individuals with major depression for a period of 8 weeks.
Before and after that time, they completed a diagnostic tool of depression known as the Beck Depression Inventory. This tool is useful to diagnose depression and its severity. After the treatment, the depression score in the treatment group was significantly lower as compared to the placebo group.
Another interesting finding was about systemic inflammation, which triggers depression by the mechanisms described above. In this study, an inflammatory marker known as hs-CRP was reduced. Insulin levels and insulin resistance improved as well, and the patients had higher levels of antioxidant enzymes (5).
Another research had a more comprehensive approach. This time, researchers evaluated not only depression but also anxiety and stress in human trials. The probiotic supplement tested in this study contained B. longum and L. helveticus. The participants were randomized to receive either the probiotic supplement or placebo. After 30 days of taking this probiotic mix, the participants experienced an improvement in depression and anxiety. They also had improvements in their capacity to solve problems and lowered their hostility and anger levels (6).
Fatigue is a common symptom of depression. These patients experience a sustained state of tiredness and low motivation. Part of being depressed makes it difficult to find the energies and will to go on with their day-to-day activities. Some of these patients also have chronic fatigue syndrome. This syndrome is also common in patients who suffer from chronic disease, and probiotics are apparently helpful to control the symptoms.
According to a double-blind clinical trial, L. casei can be useful for these patients. They were randomized into two groups, one of them receiving probiotics and the other placebo. The probiotic group received 24 billion CFUs of the bacterium L. casei every day for two months. After that time, they completed the Beck Depression Inventory and Beck Anxiety Inventory. Researchers found that people taking probiotics had lower levels of anxiety and depression than those receiving placebo (7).
There are also many early studies in animals, especially mice. Different from human studies, we can easily measure levels of serotonin in their brain after using probiotics.
In one of these animal researches, L. Plantarum was found to increase serotonin and dopamine levels in their brain. They also had a decrease in anxious behaviors while solving a maze. They had no toxic effects after consuming the probiotics, and their movement was more rapid and swift. Higher serotonin and dopamine levels were located in the striatum. This brain area is associated with reward, motivation, planning, and decision-making skills (8).
Probiotics research for stress
Stress is associated with anxiety and depression in different ways. One of the studies above evaluated stress levels along with anxiety and depression. The researchers reported that B. longum and L. helveticus could help counter the effects of stress in our nervous system.
Another interesting study was performed on stressed medical students. The researchers took healthy medical students who were about to undertake a national examination exam as a part of their promotion. They were randomized into two groups.
One group received fermented milk with L. casei. The other received placebo milk. Both groups consumed their products every day for eight weeks until the day of examination. Throughout the study, they underwent psychological studies and blood tests. They also recorded their symptoms in a diary for eight weeks.
After gathering all of the information, the researchers found that students taking probiotic milk reported fewer physical symptoms of stress, such as palpitations, rapid heartbeat, sweating, insomnia, and more. As such, stress can be modified by many things in our daily lives, and it is difficult to handle. However, according to this trial, what probiotics can do is preventing stress from causing physical symptoms (9).
Still, stress is a multifactorial problem, and it is not easy to evaluate by itself in humans. Too many factors play a role, and we can’t control them all. That’s why clinical research of probiotics for stress is so far limited. Most of them are restricted to animal trials.
One of these animal trials involved rats under stress. After 21 days of restraint stress, the rats underwent behavioral testing with an elevated-plus maze test, a recognition test, and others. They also underwent chemical analysis before starting to use L. helveticus supplements. The rats consumed the supplements every day, and their results were compared to the effects of citalopram. Researchers reported lower corticosterone levels and higher serotonin levels in the hippocampus. In other words, L. helveticus had antidepressant activity similar to that of citalopram (10).
Suggestions for a healthier gut and improved mood
The results of the clinical trials above should be interpreted with care. They do not mean that probiotics are as effective as antidepressants. What they do is highlighting the relationship between anxiety, depression, and gut microbiota.
The applications are still under research, and it is too early to reach a conclusion or recommend probiotics as a treatment for depression.
Instead of seeing probiotics as a treatment, it is wiser to use them as adjuvant therapy. A contributing factor that should be included in your daily regime to obtain better results. It may also be a way to prevent mental health symptoms with simple day-to-day recommendations.
Here’s what you can do to contribute to your gut health:
- Eat probiotic foods: Besides yogurt, there is a wide variety, including tempeh, kefir, sauerkraut, and different cheese types.
- Record gastrointestinal symptoms: If you often suffer from gastrointestinal problems, record them in a diary. Try to see if they have a connection with your emotional issues as well.
- Talk to your doctor: Report your gut symptoms to the doctor and follow his recommendations.
- Learn how to choose probiotic supplements: Look at the probiotics list above and choose a strain accordingly. Try to consume a minimum of 10 billion CFU a day.
But besides caring for your gut, it is also important to have coping strategies to deal with daily stress:
- Give yourself a break when you feel you need it
- Exercise every day
- Eat a healthy diet
- Go for a massage
- Practice meditation or mindfulness techniques
- Communicate your feelings to people who care for you
Gut health and mood are linked in many ways. The digestive tract receives commands from the central nervous system to maintain a healthy gut. The gastrointestinal tract (GI tract) also sends signals through the vagus nerve. But the gut flora plays an essential role in communication, too. This is also known as the gut-brain axis.
Gut imbalance and gastrointestinal diseases could alter normal brain function through inflammation and several hormones, contributing to stress, anxiety, and depression. Thus, modulating our intestinal microbiota does not only keep bad bacteria away. It might also help us control anxious thoughts and depressive symptoms.
Probiotics and fermented foods are sometimes useful to relieve these symptoms. They are under research and offer a promising alternative to antidepressants. More research is warranted to find applications that doctors include in the protocol against anxiety and depression. However, adopting a healthy lifestyle and consuming fermented foods and probiotics can be used as adjuvant therapy to obtain excellent results and avoid the unwanted effects of anxiety and depression.