The microbiota were also observed in human patients and

The gut of each human individual harbors up to 3.8×1013 bacteria belonging to approximately 500 – 1.000 species with the highest density in the colon, referred to as gut microbiota 1–3. The widely stated ratio of bacterial to human cell of 10:1 was recently updated to closer to 1:1 by Sender et al. 2. The gut microbiota is dominated by the phyla Firmicutes, Bacteroides, Actinobacteria, Verrucomicrobia and Proteobacteria. The diversity, composition, and metabolic functions of the gut microbiota vary highly between individuals and are influenced by diet, life-style, use of antibiotics as well as genetics 4–10. The interplay between gut microbiota and the host as well as between gut microbes themselves plays an important role in digestion, immunity, and metabolism 11, 12. Furthermore, the gut microbiota can modulate the absorption of dietary nutrients and influence the endocannabinoid system, which can further induce lipogenesis in adipocytes 13, 14. This indicates that the interplay between diet and the gut microbiota is crucial for the host’s health.Several research groups assessed the effect of diet on the gut microbiota and the development of metabolic diseases, including obesity and type-2 diabetes (T2D). In human, obesity has been associated with changes in fecal microbiota profiles, including reduction and alterations in bacterial diversity 15–19. Moreover, a negative correlation between the Bacteroidetes/ Firmicutes ratio and obesity was observed in mice and humans in some studies 16, 20–23, but not in others 24–26. Fecal microbiota profiles in T2D patients were shown to differ from that in healthy persons, although results from different studies are conflicting 27–32. These contradictory results could be due to differences in study design, number of subjects, consideration of confounders like anti-diabetic therapies and methodologies used for microbiome analysis 33, 34. Infusion of microbiota from lean donors to patients with metabolic syndrome improved insulin sensitivity and increased the abundance of butyrate-producing gut bacteria as measured by Human Intestinal Tract Chip (a custom-made Agilent microarray) 35, suggesting that manipulation of the gut bacterial ecosystem might be one opportunity to increase insulin sensitivity and thereby human health. Moreover, compositional shifts in the gut microbiota were also observed in human patients and animals with non-alcoholic fatty liver 


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