The gut and the psyche have close connexions. Anxiety, depression, and other disorders have characteristic expressions in gut behaviour – and the associations work both ways: diseases of the gut affect mind and mood. As well as containing 95% of the body’s serotonin, which also acts, as is well known, as a neurotransmitter in the brain, and is thought to be involved in affect regulation, the gut has some 200–600 million neurones, rather more than there are in the brain of a dog.15 And most of the neural traffic is from the gut to the brain, not the other way round. You can take it that they
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