Microbial cocktails are more than just a hunch

In 2023 our understanding the microbes that live in the human gut will lead to new ideas for medicine. Today we know that gut microbes help develop and maintain our immune systems. They do this by producing high levels of three types of short-chain fatty acid molecules: acetic acid, propionic acid, and butyric acid (or butyrate). The last of these, butyrate, promotes the activity of immune cells called regulatory T cells or T-regulators. These cells specialize in shutting down the activity of other immune cells, which is vital in preventing damage to the body by the immune system. Other short-chain fatty acids also affect immune cells as well as intestinal mucosal cells, although these other processes are not as well understood.

Roughly speaking, a high level of fatty acid molecules calms the immune system, creating an “anti-inflammatory” environment not only locally in the intestines, but throughout the body. There are many situations in which this feature is important, including to treat or prevent allergies.

Allergies are caused by unwanted immune reactions to substances that are mistakenly considered harmful—what we might think of as an overreaction of the immune system—so something that helps dampen immune responses, or helps the body develop the ability to do so, could be helpful in preventing allergies. .

There is some evidence that gut microbes do just that, helping the immune system develop in a way that prevents allergies. For example, mice fed a high-fiber diet produced high levels of short-chain fatty acids in their gut, which correlated with being less likely to develop the mouse version of asthma. A small study of young children also found that allergy sufferers had lower levels of short-chain fatty acids in their faeces. However, it is important to note that these observations are only correlations. Here we are at the frontier of knowledge.

In 2023, our understanding of gut microbes will deepen as technology advances. First, laboratory equipment will be used to quickly sequence large amounts of genetic material. Second, we have developed computer hardware and software that will allow us to sort through all the different microbial gene sequences, look for patterns in the data, and correlate the results with other factors such as a person’s diet or health status. The attempt to understand the human microbiome has become the flagship of big data science.

Probiotics — foods or supplements that contain live bacteria — are one way to manipulate the microbiome. There is some evidence that they may relieve the symptoms of an ongoing illness, such as irritable bowel syndrome, or perhaps help avoid the side effects of antibiotics. But the relevant authorities in Europe and the US have yet to approve any probiotic as a drug.

There is a profound scientific problem right now: with the vast variability in the exact composition of each person’s gut microbes, we don’t really know what “healthy” is. A core set of various bacteria seems important, and nothing obviously dangerous should be absent. But other than that, little is known. Perhaps more important is not a few types of microbes, but an overarching ecology. When we understand this clearly, we will be able to develop and produce healthy microbial cocktails that can be used as a medicine.