“As long as there's breath in our lungs our story is still being written.” –Bart Millard

Two chemicals from breath samples, butyrate and trimethylamine, are sufficient to distinguish depression and schizophrenia with 80 percent accuracy. These chemicals are both produced by gut microbes. This implies that the correlation between gut microbes and these two mental conditions is surprisingly robust. If, in a room full of people with multiple mental issues, you can distinguish them by their microbes, then perhaps we should be paying more attention to these microbes.

For about two decades now, we have understood that there is an intimate connection between gut microbes and mental health. But many professionals in the psychiatric field have been reticent to incorporate this knowledge into their practice. They know they have some patients with gut issues, but they also have many who seem to be free of them.

However, the gut issue is often hidden and, thus, unlikely to be encountered in normal therapy. Some psychiatrists point out that drugs already help many of their patients. Why mess with something that’s working? If only a fraction of psych patients have obvious gut issues, is it really worth pursuing?

There are several problems with this attitude. One is that drugs don’t work for many, and we don’t know why. To complicate the issue, drugs interact with gut microbes. Drugs can kill some microbes and........

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