You carry as many bacteria inside you as cells of your own

Your body is home to around 38 trillion bacteria, most of them in the gut. That is, more or less, the same number as the human cells you have.

For years we were told they outnumbered us ten to one. A more careful count in 2016 corrected the figure: the real ratio is very close to one to one. Even so, the idea is still astonishing: you are, almost in equal parts, yourself and an ecosystem.

And they are not troublesome lodgers. Those bacteria digest what you cannot, manufacture vitamins and train your immune system. Looking after them — what you eat — is looking after yourself. You are never really alone: inside you there is a multitude working to keep you on your feet.