In 2023, our understanding of 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 system. 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 latter, butyrate, promotes the activity of immune cells called regulatory T cells or T regulators. These cells are specialists in turning off the activity of other immune cells, which is vital to keep the immune system from harming the body. Other short-chain fatty acids also affect immune cells as well as cells lining the gut, although these other processes are not as well understood.
Roughly speaking, high levels of fatty acid molecules calm the immune system, creating an “anti-inflammatory” environment – not just locally in the gut, but throughout the body. There are many situations in which this function is important, including the management or prevention of allergies.
Allergies are caused by unwanted immune responses against things that are mistakenly seen as harmful – what we might think of as an overreaction of the immune system – so anything that helps dampen the immune responses, or helps the body develop the ability to do so, can 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 murine version of asthma. A small study of young children also found that those with allergies had lower levels of short-chain fatty acids in their feces. However, what is important is that these observations are only correlations. We are here at the edge of knowledge.
In 2023, our understanding of gut microbes will deepen thanks to advances in technology. First, laboratory equipment will be used to rapidly sequence large amounts of genetic material. Second, we have now 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 – products or nutritional supplements with the addition of live bacteria – are one of the perspectives of manipulating the microbiome. There is some evidence that they can ease the symptoms of a long-term illness, such as irritable bowel syndrome, or perhaps help avoid the side effects of taking antibiotics. But the relevant authorities in Europe and the US have not yet approved probiotics as medicines.
Now there’s a profound scientific problem: Because of the enormous variability in the exact makeup of each person’s gut microbes, we don’t really know what “healthy” is. A core set of different bacteria seems important, and something obviously dangerous must be missing. But apart from that, little is clear. Rather than a few types of microbes, perhaps the overarching ecology is important. Once we understand this clearly, we will be able to design and produce healthy microbial cocktails that can be used as medicine.