A “physical examination” is the standard way to track human health. It involves a variety of measurements such as blood pressure, cholesterol levels, body-mass-index, cognitive index, bone density, vitamin and mineral status etc. Those measures are important, but it is becoming increasingly clear that our health is also influenced by what is going on with our “gut microbiome” – the huge and diverse communities of bacteria, viruses and fungi that live in our intestines and stomach.