In 1898, an American psychiatry professor named Daniel Brower came up with an odd idea he called “auto-intoxication”. In
a paper he sent to the
Journal of the American Medical Association, he suggested that an excess of bacteria in the gut could, via the production of bacterial waste products, cause “melancholia” – what we now know as depression. The body was literally toxifying itself, producing chemicals in its own gut that had ramifications for organs far beyond the intestine.
It was the start of what has become an on-and-off fascination for medical scientists: the idea that the micro-organisms in our digestive system might have effects on our minds, and specifically, on our mental health.
And for the past decade or so, scientists have been very much in the “on” phase. Look anywhere in the recent medical literature and you’ll find claim after claim about the potential impact of the “microbiome” – the collection of microbes we all carry around with us – on our brains. Depression, anxiety, schizophrenia, bipolar disorder, autism – you name it, a scientist has written a paper pointing to how it’s affected by the “
gut-brain axis”, the hypothesised set of links between what goes on with our microbiome and what goes on with our minds.
However, a lot of those papers are just scientists’ opinions. One of the strange things you notice when reading about the gut-brain axis is that there are an awful lot of opinion and “review” articles on the topic – many more than for the average scientific topic. It’s even
been suggested that there are more opinion pieces than there are empirical studies providing new evidence on this question. That’s a red flag: when there are more theories than data with which to test them, you’re usually on shaky ground, scientifically.
