I have some startling news: you are not human. At least, by some counts. While you are indeed made up of billions of human cells working in remarkable concert, these are easily outnumbered by the bacterial cells that live on and in you – your microbiome. There are ten of them for every one of your own cells, and they add an extra two kilograms (4.4lbs) to your body.
Far from being freeloading passengers, many of these microbes actively help digest food and prevent infection. And now evidence is emerging that these tiny organisms may also have a profound impact on the brain too. They are a living augmentation of your body – and like any enhancement, this means they could, in principle, be upgraded. So, could you hack your microbiome to make yourself healthier, happier, and smarter too?
According to John Cryan, this isn’t as far-fetched as it sounds. As a professor of anatomy and neuroscience at University College Cork, he specialises in the relationship between the brain and the gut. One of his early experiments showed the diversity of bacteria living in the gut was greatly diminished in mice suffering from early life stress. This finding inspired him to investigate the connection between the microbiome and the brain.
The bacterial microbiota in the gut helps normal brain development, says Cryan. “If you don’t have microbiota you have major changes in brain structure and function, and then also in behaviour.” In a pioneering study, a Japanese research team showed that mice raised without any gut bacteria had an exaggerated physical response to stress, releasing more hormone than mice that had a full complement of bacteria. However, this effect could be reduced in bacteria-free mice by repopulating their gut with Bifidobacterium infantis, one of the major symbiotic bacteria found in the gut. Cryan’s team built on this finding, showing that this effect could be reproduced even in healthy mice. “We took healthy mice and fed them Lactobacillus [another common gut bacteria), and we showed that these animals had a reduced stress response and reduced anxiety-related behaviours.”
But why should bacteria in the gut affect the brain? There are several different ways that messages can be sent from one organ to the other. It can be hormones or immune cells via the bloodstream, or by impulses along the vagus nerve, which stretches from the brain to intertwine closely with the gut. Through these pathways, actions in one produce effects in the other.
So how might you go about altering your microbiome to do a spot of brain-hacking? Cryan’s team works on several fronts, investigating the potential to manage stress, pain, obesity and cognition through the gut. “We have unpublished data showing that probiotics can enhance learning in animal models,” he tells me. His team tested the effects of two strains of bacteria, finding that one improved cognition in mice. His team is now embarking on human trials, to see if healthy volunteers can have their cognitive abilities enhanced or modulated by tweaking the gut microbiome.
Another method of adjusting the bacterial profile of your gut is to undergo a transplant that involves taking faecal material from a donor’s intestine – often a close relative – and implanting into a recipient via enema infusion. This unorthodox treatment has been shown to successfully treat infections caused by pathogenic bacteria colonising the gut.
Thankfully, Cryan has a far more appetising method on offer. “Diet is perhaps the biggest factor in shaping the composition of the microbiome,” he says. A study by University College Cork researchers published in Nature in 2012 followed 200 elderly people over the course of two years, as they transitioned into different environments such as nursing homes. The researchers found that their subjects’ health – frailty, cognition, and immune system – all correlated with their microbiome. From bacterial population alone, researchers could tell if a patient was a long-stay patient in a nursing home, or short-stay, or living in the general community. These changes were a direct reflection of their diet in these different environments. “A diverse diet gives you a diverse microbiome that gives you a better health outcome,” says Cryan.
Beyond a healthy and varied diet, though, it still remains to be discovered whether certain food combinations could alter the microbiome to produce a cognitive boost. In fact, Cryan recommends that claims from probiotic supplements of brain-boosting ought to be taken with a pinch of salt for now. “Unless the studies have been done, one can assume they’re not going to have any effect on mental health,” he says. Still, he’s optimistic about the future. “The field right now is evolving very strongly and quickly. There’s a lot of important research to be done. It’s still early days.”
Hacking the brain often conjures up ideas of electrical hardware such as implants and trans-cranial stimulators. But it might be the case that a simple change in diet can shift your brain up a gear. The transhumanists and body hackers who believe that technology is the sole way to improve human ability would do well to pay as much attention to the living augmentation that already resides in their gut.