Changes in the fecal flora composition of human volunteers in a double-blind randomized black tea feeding study

The importance of the microbial intestinal flora in human cancer and other disease has long been postulated. The effects of some dietary substances, such as prebiotics, on the composition of the flora have been established. The effects of diet on health may be mediated in part by changes in the composition of the intestinal flora. Black tea has been suggested to affect cancer risk, although evidence for this association is equivocal. Polyphenols in black tea could alter the bacterial flora, leading to an increased excretion of carcinogenic fecal bile acids. We analyzed changes in the fecal flora composition and in the fecal bile acid profile in 15 subjects in a black tea feeding study. Fecal samples were collected on d 1, 13 and 20 of the two periods (crossover design) for a total of six samples from each volunteer. We performed fluorescent in situ hybridizations (FISH) and temporal gradient gel electrophoresis (TGGE) to analyze the bacterial flora and determine changes in the bile acid profile enzymatically and by HPLC. Large inter- and intraindividual variation masked any small effects of diet or black tea on the flora composition. However, we did observe a decrease in the amounts of 'other bacteria' detected only by the universal bacterial probe in the FISH analysis. TGGE analyses showed a distinct bacterial profile for each subject that was relatively stable over time. These results indicate that tea drinking affects some flora components, but more sensitive tools and larger studies are required to evaluate effects of diet on the intestinal flora.