Medieval physicians believed that they could diagnose disease by holding up a flask of the patient’s urine to the light and squinting at it. According to scientists at Imperial College London, they could have been on to something.

A team there has completed the first worldwide study of the metabolites (breakdown products) that are found in urine, reflecting the diet, inheritance and the lifestyle of the people from whom it came. They call such studies “metabolomics” by analogy with genomics, which looks at all the genes that make up the human species, and proteomics, which does the same for proteins.

The study used nuclear magnetic resonance spectroscopy to compare racial and national groups by the composition of their urine. From Japan, Beijing, Corpus Christi, Belfast and West Bromwich, urine differs in subtle ways that could provide a powerful new way of linking diet and health.The metabolites they found come from microbes in the gut, from diet and from the metabolism of the host.