perhaps because of early life exposures and “priming” of the microbial systems.

Gut Microbial Metabolism of Plant Lignins

As a final example of the impact of the microbiome on host metabolism of dietary components, Lampe mentioned plant lignins. A whole host of plant lignins can be found in seeds, nuts, berries, grains, and other foods, most of which are metabolized into enterodiol and sometimes further converted into enterolactone. Kuijsten et al. (2005) reported highly variable enterodiol and enterolactone production among individuals. Lampe and colleagues measured microbiome diversity for low-, intermediate-, and high-enterolactone excretors among 115 women and detected significant differences between the low and high excretors and between the intermediate and low excretors. The greatest diversity was among high excretors and the least diversity among low excretors. suggesting that microbial diversity may be associated with enterolactone production. That diversity appears to be distributed across phyla, with high excretors having 20 unique genera.

BIOGEOGRAPHY OF THE GI TRACT

During the open panel discussion at the end of the first day, there was some discussion around the fact that most human microbiome studies to date are based on fecal sampling. Workshop participants expressed varying opinions about whether microbes and metabolites in the feces reflect what is happening in the gut. One audience member said, “I think you are looking in the wrong place, checking stool.” He suggested sampling the small intestine, where bacterial overgrowth is a problem in patients with small-bowel disturbances. There are sampling technologies available, he said. Another audience member agreed and noted that he and his gastroenterology colleagues are beginning to collect these samples in some of their pediatric patients. Yet another audience member asked if anyone has ever compared feces microbiota to microbiota from various portions of the gut.

Vincent Young described feces as the “summary statement of your gut.” In his opinion, feces has most of what exists elsewhere in the GI tract. It may not provide any indication of the relative abundance of species at various points upstream, but it does provide “some indication” of what is there. However, he emphasized that the usefulness of feces sampling depends on the research question. In some cases, it may not be a good choice. He noted that samples have been collected from various places along the length of the human GI tract and that they reveal both longitudinal and axial differences in both 16S rRNA and metagenomic microbial sequences.

Peter Turnbaugh remarked that based on his observations in mice, while



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