90% of the normal human gut flora is populated by two phylogenetic groups which exist in a symbiotic balance.Bacteroides are anaerobic, gram-negative bacteria which are part of the normal gut flora of the intestinal tract. In the large intestine, approximately 10 Bacteroides/g stool exist and are therefore the dominant bacteria in terms of numbers. The second phylogenetic group is the firmicutes. Clostridium Cluster XIVa are a class of firmicutes to which, besides others, Eubacterium spp. and roseburia spp. belong.

Different sources associate a disbalance of the composition of the gut flora (dysbiosis) with obesity. Here, a decreased number of Bacteroides corresponds to presence of obesity whereas at the same time an increasing number of Eubacterium rectale was detected in patients with obesity.