• Obesity
• microbiota
• enumeration

The amount of energy that is stored in the body depends on the balance between energy intake and expenditure: when energy intake exceeds expenditure, excess energy is stored as fat, which leads to weight gain and eventually obesity. A number of factors are associated with the obesity epidemic that is spreading worldwide, such as individual genetic predisposition, diet and lifestyle. Recently, the community of microbes colonising the gastrointestinal tract, the gut microbiota, has been recognised as one such factor.1–3 Studies on mice maintained under germ-free conditions have shown that the gut microbiota promotes increased adiposity by enhancing energy extraction from food and modulating host genes that regulate fat storage.1

Culture independent analyses of the composition of the gut microbiota have revealed that obese individuals harboured a varied proportion of two prevailing phyla, Firmicutes and Bacteroidetes, in comparison to lean subjects.4 Furthermore, the obese metagenome, which is the set of all genes present in the genomes of gut microbes, was enriched in gene functions associated with carbohydrate and lipid metabolism.5 Both in animal and human studies, obesity has been linked to a different composition of the gut microbiota. However, results from different studies are not concordant as to the contribution of specific components of the gut microbiota to the pathogenesis of obesity …