GUT by Giulia Enders: a book review

by George Hatjoullis

I do not normally do book reviews and certainly not on medical subjects. Indeed, this book came to my attention not because of the medical basis but because of the psychology connection. In addition to degrees in economics and econometrics I have two degrees in Psychology and am an, albeit passive, member of the British Psychological Society. I read the Psychologist religiously and follow-up on books and research of interest. My main personal interest is the connection between mind and body, so subjects such as Placebo fascinate. This book highlights a link between the mind and the digestive system of which I had not been aware. Anyone interested in this subject might wish to take a look.

In the foreword, the author reveals that she had first become aware of a possible link between the gut and psychological state when she encountered a man with unusually bad breath who committed suicide the next day. Not a great basis for postulating a hypothesis i would have thought but it does seem to have inspired the author. The book is a very accessible description of the operation of the digestive system, with some useful insights, but it is the psychological aspects that will be reviewed.

The gut it seems is linked to the brain and the most important link is the vagus nerve. The author describes an interesting experiment with mice. In order to test antidepressants, mice are used in a swimming test. Mice with depressive tendencies tend not to try hard to keep swimming when drowning is inevitable and if the test antidepressant keeps them swimming longer it is deemed a potentially useful medication. In a variation on this experiment, half of the depressed mice were fed a bacteria known to be good for the gut. These mice swam for longer and had less stress hormone in their blood stream. They also performed better in memory and learning tests. However, when the vagus nerve was severed, the two groups performed exactly the same. Recent research repeated on humans seems to support these findings. Good bacteria will affect your psychological state and so will a lack.

Toxoplasma gondii provides another very interesting example of the connection between the gut and the brain and one of which cat-lovers ought take particular note.Toxoplasma gondii are parasites that reproduce in the gut of cats but will use any other creature to move from cat to cat. They are particularly dangerous for pregnant mothers but this is not the issue of interest. Rats, normally averse to the smell of cat urine, were found to lose this aversion when infected with toxoplasma. The conclusion was that the toxoplasma inhibited the rat survival instinct enabling the cat to eat it and thus for the toxoplasma to achieve a new cat host. What a brilliant parasite! It turns out however that humans infected with toxoplasma are much more likely to be involved in car accidents. Indeed Toxoplasma gondii are even implicated in schizophrenia cases.  Cats can be bad for your health.

These two examples suffice to illustrate that the gut and its bacteria can have a causal relationship on the psychological states. This is an area of research in psychology and medicine that has not seen much activity until very recently. This book is a very effective tool for raising awareness among the general public as well as professionals too immersed in their own little specialism to look up.