An individual's intestinal bacteria flora falls into certain patterns that are independent of nationality, gender, and age according to a 2011 article in the journal, Nature. They believe that the composition of the GI microflora is a new biological fingerprint, just as our blood type or tissue type.
We depend on our GI microflora to metabolize hormones, carcinogens, and toxins, synthesize vitamins K, B5, B6, and biotin, crowd out pathogenic bacteria, and stimulate our immune systems. When the microflora is abnormal it can cause maldigestion, malabsorption, consumption of vitamin B12, destruction of essential fatty acids, leaky gut syndrome, yeast overgrowth, and IBS.