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Gut Bacteria and Depression

Estimated reading time: 45 minute(s)

The human gut, frequently known as the second brain, is home to millions of microorganisms controlling overall health. Recent research has highlighted how these tiny gut bacteria, also known as the gut microbiome, can impact overall mental health, particularly when it comes to problems like depression.

Exploring the relationship between gut bacteria and depression is now considered a key to finding appropriate management strategies for long-term health.

A Brief Overview of the Gut-Brain Connection

The gut and the brain share a close relationship, often known as the gut-brain axis. [1] This communication involves hormones, nerves, and immune system signals with gut bacteria playing a significant role in between. The vagus nerve is the most important neural connection that joins the brain with the gut. It maintains a bidirectional connection, meaning whatever goes on in the brain affects the gut and vice versa.

The gut microbiota is another important factor influencing the gut-brain axis. This community of microorganisms resides in the digestive system and includes various fungi, viruses, bacteria, and other microbes that support overall health. Each individual has a unique microbiome composition based on the environment, diet, genetics, and overall lifestyle.

While some bacteria in the gut microbiome are harmful, many help the body by protecting it from infections, synthesizing crucial vitamins and hormones, and helping with digestion. Maintaining a balance between the good and bad bacteria in the gut is imperative to sustain overall health. Any imbalance between the two leads to dysbiosis which, in turn, makes the body a breeding ground for depression and other mental health issues. [2]

Gut Bacteria and Depression: Evaluating How Gut Bacteria Affect Mood

Following are some proposed theories about how gut bacteria can affect mood and likely increase the risk of depression:

Synthesis of brain chemicals

The gut bacteria are responsible for producing many important brain chemicals, such as GABA, dopamine, and serotonin. These chemicals are mood regulators and can increase the risk of depression, if not produced appropriately. Serotonin, also known as the happy chemical, is the most crucial as it significantly contributes to happiness and well-being. Research suggests that up to 90 percent of its production takes place in the gut. [3]

Inflammation

When the gut bacteria are imbalanced, it can trigger a condition called leaky gut. A leaky gut allows harmful toxins to enter the bloodstream, triggering high levels of inflammation. This high inflammation, in turn, increases the risk of depression.  The pro-inflammatory cytokines triggering this inflammation can cross the blood-brain barrier and interrupt brain function.

Short-Chain Fatty Acid Production

The gut microbiome is responsible for breaking down fiber from food to synthesize short-chain fatty acids (SCFA). These SCFAs can affect brain function and settle inflammation. Certain SCFAs, such as butyrate, possess anti-inflammatory properties that control the inflammation levels in the brain to lower the risk of depression and manage its symptoms. [4]

Glutamate Transmission

Research indicates that glutamate transmission overactivity in the brain can contribute to anxiety and depression. The gut microbiome keeps this transmission in check by producing GABA and serotonin neurotransmitters. This neurotransmitter-mediated inhibition of glutamate activity can also help maintain mental health.

Stress Management

Gut bacteria frequently interact with the stress response system in the body to keep it under control by limiting the release of cortisol, the stress hormone. In the case of dysbiosis, the body keeps secreting cortisol without any check or balance, making an individual more prone to stress and depression.

Depression and Gut Health: Research Propositions

Extensive research has been performed on the subject of gut bacteria and depression. The most authentic insights available so far are summarized below:

Animal Trials

Research using animal models has given experts valuable insights regarding the gut-brain axis. For instance, studies have shown that germ-free mice who were raised in the lab without any gut bacteria have a higher risk of acquiring depressive behaviors and high stress levels than normal mice. incorporating certain bacterial strains helped the germ-free mice to reverse depressive behaviors, confirming the role of gut bacteria in regulating mood. [5]

Further studies have found that transferring gut microbiome from depressed humans to germ-free rats can induce depression in the latter. This insight confirms the role of the gut microbiome in regulating mood and depressive disorder.

Human Trials

So far, human trials have also confirmed the link between gut bacteria and depression. Research demonstrates that people with underlying depression have different gut microbiomes than those without this psychiatric illness. For instance, the levels of certain beneficial bacteria, like Lactobacilli and Bifidobacteria, are lesser in depressed individuals than those without any mental health disorders. [6]

Further research also confirmed the specific bacterial strains associated with depression. Experts believe that individuals with depression have lower levels of Coprococcus and Faecalibacterium., two important bacterial strains known for their potent anti-inflammatory properties.

Supplement Trials

Trials using probiotic and prebiotic supplements have confirmed promising results in managing depression symptoms. Many trials have concluded probiotics to possess a strong antidepressant effect through optimization of the gut microbiota. Taking probiotics for eight weeks has also been shown to improve mood and reduce anxiety and depressive symptoms.

How to Prevent Poor Gut Health for Better Mental Health: Key Areas to Focus

Regardless of the nature of the underlying medical issue, prevention is always better than cure. Since a healthy gut is the key to a healthy brain, focusing on digestive health should be the key focus.

The most obvious place to start in this regard is the environment, as it has the largest modifiable impact on gut health. Environmental changes require a lot of effort and cooperation from an entire community. Individuals can also make necessary efforts to contribute to better gut health by altering the environment surrounding them.

Some areas to focus on for better gut health include the following:

  • Diet: Since food directly goes to the gut, it has the most impact on the overall gut health. Hence, raising awareness about healthy eating choices and supporting them in the community is imperative. Specific foods to focus on include high-fiber vegetables and fruit. On a community level, these foods must be made affordable so a maximum number of people can access them.
  • Stress: Reducing stress is one of the most difficult interventions to improve gut bacteria and depression. As a proven trigger for gut problems and mental health disorders, stress reduction must be a part of life.
  • Medication Side Effects: Medicines are known to disrupt gut health. Antibiotics, in particular, can kill off healthy bacteria in the gut while attempting to ward off infections, often leading to imbalances, also called dysbiosis. Research now confirms that 24 percent of the drugs currently available in the market are likely to affect at least one bacterial strain in the gut negatively. To minimize these side effects, being mindful of medication choices is important.

Gut Microbiome and Depression: Potential Treatment Avenues

Unfortunately, preventive measures alone are never successful in keeping an ongoing issue under control. Hence, it is imperative to look beyond prevention ideas to explore the potential treatment avenues. Presently, the following management techniques are of the prime focus in keeping gut bacteria and depression under control.

Prebiotics, Probiotics, and Psychobiotics

Probiotics are a type of dietary supplements that include live bacterial strains. With growing popularity over the last decade, probiotics are known to supplement the gut with beneficial bacteria to manage imbalances. Getting probiotic-rich food, such as yogurt, kefir, and kombucha is deemed the best to enjoy the benefits with minimal side effects.

However, with time, mixed opinions have emerged regarding the impact of probiotics as treatment. Many experts now consider it more suitable as a preventive strategy as using them provides the right environment for gut bacteria to thrive.

Prebiotics are another type of gut supplements that provide food and nourishment to the gut microbiome. These supplements bypass the normal digestive processes and travel directly to the gut where the bacteria consume them. Prebiotics are naturally found in onions, garlic, soy, wheat, and artichoke. Taking them together with a probiotic increases their chances of survival; hence, they are often available in combinations called synbiotics.

Psychobiotics are a newer entry into the supplement market. These are a special class of probiotics that specifically regulate mood and other brain functions. These mixtures are more specific to the gut bacteria and spare the ones present in other parts of the body, an effect that most probiotics lack. As research continues to explore different supplements regarding gut and mental health, most experts are now inclining toward using synbiotics as the most favorable supplement.

Fecal Microbiota Transplantation (FMT)

This evolving technique involves the transference of gut bacterial strains taken from a healthy person to a person fighting depression. Preliminary trials have suggested FMT as a promising treatment; however, more research is needed to confirm it.

Smaller studies have found that FMT from healthy donors to those with depression led to massive improvements in mood with a reduction in depressive episodes. Similar improvements have been seen in people with anxiety, schizophrenia, and bipolar disorder. Some studies have also considered fecal transplants to be more beneficial than probiotics. However, with the technique still in the experimental phases, more research is needed to determine its safety. [7]

Herbal Cures

Many Eastern methods have been in use to target the gut-brain axis for centuries. However, they are very rarely included as a part of an integrative approach, possibly due to a lack of open-mindedness. Research trials now support many of these herbal methods to combat gut issues and modulate mental health.

Animal trials involving Chinese herbal medicine have proven that these treatments can increase stress tolerance by altering the gut microbiome. [8] However, many have raised the question of whether the same results are achievable in human models. At the same time, many other Chinese medicines have been confirmed to modulate the microbiome while maintaining the integrity of the internal barriers to prevent leakiness.

How to Improve Gut Health For Depression: A Practical Guide

Considering the strong relationship between depression and gut health, the following are some practical steps to support both:

Eat mindfully

Consider blending fiber-rich vegetables, fruit, legumes, and whole grains into your daily diet. These foods give the gut bacteria the necessary nutrients to flourish and thrive. Fermented foods, like sauerkraut, kefir, kimchi, and yogurt are also beneficial as they contain live bacteria that support the microbiome and boost gut health. Optimizing gut health by eating healthily can help with depression management.

Say no to processed foods

Processed foods contain a high level of unhealthy fat and sugar which negatively alter the gut microbiota. Limiting their intake and replacing them with whole, unprocessed foods is the best way to secure sound mental and gut health.

Maintain adequate hydration levels

Drinking plenty of water is recommended to maintain gut health. Water supports digestion while regulating the functions of the gut microbiome which, in turn, ensures better mental health.

Manage stress

Chronic stress can negatively impact the gut bacteria and worsen depression. Effective stress management strategies, such as deep breathing exercises, yoga, meditation, exercises, or simply spending time in nature can lower stress levels to benefit gut bacteria and depression.

Workout regularly

Regular physical activity can positively impact gut health which, in turn, keeps depression at bay. Aim to get 30 minutes of exercise up to three to four times a week to enjoy the benefits.

Get enough high-quality sleep

Sleeping is essential for overall health as it is when the body is rejuvenating and restoring itself. Aim to get 7-8 hours of sleep every night and practice a good sleep hygiene routine to improve sleep quality.

Consider taking a probiotic supplement

Consult with a healthcare provider about the possibility of including a probiotic supplement in your daily life. A trained expert can advise how to choose the right strain and the correct dose to use for optimal benefits. Probiotics can boost the levels of friendly bacteria in the gut to positively influence gut bacteria and depression management.

Happy Gut, Happy Mind

Research now proposes various theories about gut health linked to depression. This gut-brain connection is intricate and may require adjustments in people struggling with frequent gut issues and depressive episodes. Contacting a healthcare professional is the best way to seek personalized guidance based on your health requirements and pre-existing issues.

In addition to the conventional treatments available for mental health disorders, like psychotherapy and medications, lifestyle and dietary modifications aiming to improve the working of the gut can also prove beneficial.

Through a combination of dietary adjustments, supplementation, and healthy lifestyle choices, it is possible to regulate microbiome and depression. While scientists continue to explore the gut-brain axis, many future avenues are likely to emerge to keep the gut and brain healthier and far from issues.

FAQs

Can gut microbiome cause depression?

While gut bacteria cannot directly trigger depression, they are one of the many contributory factors to its development and severity. Any imbalances in the gut flora, a condition known as dysbiosis, have been widely observed in people struggling with depression. Research suggests that restoration of a healthy gut microbiome through probiotics, diet, stress management, and other lifestyle management tips can improve mood in many cases.

What is the role of diet in regulating gut microbiome and depression?

Diet has a crucial role in maintaining a balanced gut microbiome which, in turn, positively regulates mood. Consuming a diet rich in fruit, vegetables, fiber, and fermented foods nourishes the gut bacteria. On the other hand, eating highly processed, sugar-loaded food can cause dysbiosis, leading to inflammation and mood dysregulation.

What should I do if I feel my gut health is negatively impacting my mood?

If you suspect that your ongoing gut issues are affecting your mood, get in touch with a healthcare professional. These professionals can assess the symptoms and advise appropriate testing to confirm or rule out any underlying causes. Based on assessments, a healthcare expert can guide you about probiotics, dietary changes, and other interventions that can potentially help you.

Are there any risks of using probiotics or changing dietary habits to improve gut bacteria and depression?

Dietary management, including using probiotics, is generally safe for most people. However, some users may experience mild digestive issues after using probiotics or increasing their fiber intake. To minimize these risks, go slow and gradually introduce any changes in daily life. Focus on one thing at a time and seek professional help if you have any serious concerns.

References

[1] Carabotti M, Scirocco A, Maselli MA, Severi C. The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems. Annals of gastroenterology: quarterly publication of the Hellenic Society of Gastroenterology. 2015 Apr;28(2):

[2] Liu L, Wang H, Chen X, Zhang Y, Zhang H, Xie P. Gut microbiota and its metabolites in depression: from pathogenesis to treatment. EBioMedicine. 2023 Apr 1;90.

[3] Chen Y, Xu J, Chen Y. Regulation of neurotransmitters by the gut microbiota and effects on cognition in neurological disorders. Nutrients. 2021 Jun 19;13(6):2099.

[4] Tedelind S, Westberg F, Kjerrulf M, Vidal A. Anti-inflammatory properties of the short-chain fatty acids acetate and propionate: a study with relevance to inflammatory bowel disease. World journal of gastroenterology: WJG. 2007 May 5;13(20):2826.

[5] Nishino R, Mikami K, Takahashi H, Tomonaga S, Furuse M, Hiramoto T, Aiba Y, Koga Y, Sudo N. Commensal microbiota modulate murine behaviors in a strictly contaminationā€free environment confirmed by cultureā€based methods. Neurogastroenterology & Motility. 2

[6] Johnson D, Letchumanan V, Thum CC, Thurairajasingam S, Lee LH. A microbial-based approach to mental health: the potential of probiotics in the treatment of depression. Nutrients. 2023 Mar 13;15(6):1382.

[7] Suez J, Zmora N, Zilberman-Schapira G, Mor U, Dori-Bachash M, Bashiardes S, Zur M, Regev-Lehavi D, Brik RB, Federici S, Horn M. Post-antibiotic gut mucosal microbiome reconstitution is impaired by probiotics and improved by autologous FMT. Cell. 2018 Sep

[8] Ye C, Qu Q, Bai L, Chen J, Cai Z, Sun J, Liu C, Shi D. Effect of Traditional Chinese Medicine on the Gut Microbiota in Heat-Stressed Laying Hens. Frontiers in Veterinary Science. 2022 Jun 21;9:905382.

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