Gut flora: a new factor affecting anxiety

Anxiety is a very common emotional state. The incidence of anxiety disorders has also been on the rise in recent years. Currently, a considerable number of anxiety patients do not respond well to conventional treatments. Recent studies have shown that the diversity and types of intestinal flora are related to anxiety and depressive behaviors.

The microbial community in the human intestine is large in number and complex in structure, and is known as the second brain of humans. More and more studies have shown that the intestinal microbiome - the trillions of microorganisms in the intestine - plays an important role in the immune system and metabolism by providing essential inflammatory mediators, nutrients and vitamins. In addition, intestinal microorganisms can affect brain function and behavior through the microbiota-gut-brain axis [1].

The human genome consists of about 25,000 genes, but the microbiome in our gut expresses about 3 million different genes. These genes help build molecules that help us digest food, prevent the proliferation of harmful microbes, and even help us feel our emotions. Bacteria in our gut produce about 90% of our serotonin, which regulates mood and promotes health. In 2009, when researchers sampled and sequenced the gut bacteria of stressed mice, they found that the stressed animals, and those more likely to have mental health problems, had a lower diversity of gut microbes, or microbiomes [1].

Over the past decade or so, a growing number of labs have discovered that gut bacteria produce a wide range of compounds that can affect the human brain. For example, some bacteria in the genus Clostridium produce propionic acid, which can improve inflammation and produce dopamine and serotonin, which regulate mood. Microbes such as Bifidobacterium increase the production of butyrate, an anti-inflammatory substance that prevents intestinal toxins from entering the brain. When a group of stressed-out mice were given a regular dose of Bifidobacterium gut microbes for five weeks, they became more flexible and active than before, and were more willing to interact and explore [2].

Since 2016, a number of innovative studies have shown that fecal transplants can affect emotional behavior. Fecal transplants have been used in some intestinal diseases and mental and psychological disorders, including irritable bowel syndrome and autism, and most studies have shown that patients' symptoms have improved [3]. In one study, when mice received fecal transplants from other healthy mice, their behavior remained unchanged. But when mice received fecal transplants from patients with signs of anxiety and depression, the mice began to show signs of emotional disorders. And when stressed mice received fecal transplants from stress-free animals, their emotions were greatly alleviated [2].

It can be seen that the intestinal flora can affect the occurrence and development of anxiety, depression and related behaviors by affecting multiple factors such as neuroendocrine, stress pathways and cytokines and regulating our central and peripheral nervous systems. In the future, as more research on intestinal flora and anxiety and depression is carried out, it will be more conducive to the diagnosis and treatment of these mental illnesses.

References

[1] Zhang Yi, Zhao Yingying, Zhao Jingjie, et al. Research progress on the effects of intestinal flora on anxiety and depression. Journal of Clinical and Experimental Medicine, 2018, 17: 3

[2] Yang B, Wei J, Ju P, et al. Effects of regulating intestinal microbiota on anxiety symptoms: A systematic review. General psychiatry, 2019, 32:

[3] Meng Danli, Guo Xianwen, Liang Liexin. Research progress on the relationship between intestinal flora and anxiety and depression. Journal of Clinical Digestive Diseases, 2018, 30: 4