The human gut contains a vast number of microorganisms known collectively as the 
"gut microbiota". Despite its importance in maintaining the health of the host, 
growing evidence suggests the gut microbiota may also be an important factor in 
the pathogenesis of various diseases, a number of which have shown a rapid 
increase in incidence over the past few decades. Factors including age, 
genetics, and diet may influence microbiota composition. We used diet 
inventories and 16S rDNA sequencing to characterize fecal samples from 98 
individuals. Fecal communities clustered into previously described enterotypes 
distinguished primarily by levels of Bacteroides and Prevotella. Enterotypes 
were associated with long-term diets, particularly protein and animal fat 
(Bacteroides) vs. simple carbohydrates (Prevotella). Although the distinction of 
enterotypes as either discrete clusters or a continuum will require additional 
investigation, numerous studies have demonstrated the co-exclusion of the 
closely related Prevotellaceae and Bacteroides genera in the gut microbiota of 
healthy human subjects where Prevotella appears to be a discriminatory taxon for 
residence in more agrarian societies. Ultimately, the impact of diet on the 
human gut microbiota may be an important environmental factor involved in the 
pathogenesis of disease states that show a rapidly increasing incidence in 
industrialized nations such as the inflammatory bowel diseases (IBD).