Most revolutions have begun in the head – or even higher up, in the clouds. When the Greek comic playwright Aristophanes came to satirise his fellow-Athenian Socrates, in his play The Clouds, he called the philosopher’s imaginary world “Cloud-Cuckoo-Land”. Starting with Socrates’ pupil Plato, philosopher after philosopher has redrawn the map of humanity with ideas; they have held that the secret of turning around the benighted vision of human beings, chained in their cave facing away from the sun, lay in the most rarefied essence of thought. Even though Karl Marx announced a new philosophical praxis that would change the world, and not merely interpret it, Marx’s prescriptions generated unprecedented waves of ideological interpretation.

But I have also come to learn from a philosopher-physician whose revolution starts, quite literally, in  the gut. Dr Franz Xaver Mayr was  the Austrian doctor who became convinced that most of 20th-century Western man and woman’s problems were digestive. One of the first connections he made was between the the digestive tract and the spine. Patients who came to him with terrible posture, and related back, neck, shoulder and leg pain, soon revealed swollen and sagging livers and bellies. The pressure of these distended organs was distorting their spinal structure, causing no end of misery. The connections, Mayr realised, went further: bad eating habits led to bad digestion, affecting not just the digestive tract and the organs of cleansing – the liver, gall-bladder and kidneys – and then the spine and posture, but also the heart and lungs. Eating affected the beauty and smoothness of the skin – even, ultimately, the mind and spirit.