Each of us has around 100,000 billion viable microbes living in our intestines, comprising over 1,000 different species and more than 5,000 strains. These microbes weigh around 1.5 kg in total and are referred to collectively as the microbiome.
95% of the microbiome is in the large intestine, with only around 50g (weight) of the microbiome residing in the small intestine.