Why is it that if an individual has this condition we call a Hypo lactasia, so basically they're intolerant to lactose, and if they actually ingest the lactose, there will be a build up of the lactose. But why is that build up? Or why does the build up actually lead to these problems? Well, in our gut we basically have many, many bacterial cells. In fact, we have ten times as many bacterial cells as the cells inside our body. We have over 100 trillion bacterial cells inside our body, inside our gut, and this is about £3 of bacterial cells.