There are more microbial cells in our bodies than there are human cells! In fact 95% of all the cells in the body are bacteria, mainly living in the digestive tract. There are more bacteria in the colon than the total number of people who have ever lived. Everyone has about 1 kg in weight of bacteria in their gut. Each gram of faeces contains 100,000,000,000 microbes. Human adults excrete their own weight in faecal bacteria every year.