the periphery of the networks. Turnbaugh explained that the periphery represents interaction with the host or environment (e.g., intake of a substance from the host or environment), as opposed to glycolysis or some other core component of metabolism. As was the case with the obesity-associated genes detected by Turnbaugh et al. (2009a, 2010), many of the obesity network genes are involved in carbohydrate metabolism as well as carbohydrate transport, nitrate reduction, and xenobiotic metabolism.

Impact of Gastric Bypass on Gut Microbiota: More Evidence of Co-Metabolism by Microbes and Their Host?

Evidence from gastric bypass surgery experiments suggests that gut microbiota impact more than host energetics—they impact host metabolism at large. Turnbaugh reiterated what Jeremy Nicholson had mentioned during his presentation about the metabolic consequences of gastric bypass surgery happening too quickly to be explained by the change in caloric intake. Turnbaugh was curious about the potential role of the gut microbiota as a mediator of these rapid metabolic changes. Using Roux-en-Y-operated mice and comparing them to two different types of controls (sham and weight-matched sham mice), Turnbaugh and colleagues (Alice Liou and Lee Kaplan, Massachusetts General Hospital) observed a significant difference in how quickly the microbial community structure changed after surgery. The microbiota of all the mice changed following their respective surgeries, but the microbiota of the Roux-en-Y-operated mice changed much more dramatically within the first week following surgery. Turnbaugh remarked that the next step is to see if some of the metabolic outcomes triggered by gastric bypass surgery can be transferred to germ-free mice via the gut microbiota.

Impact of Diet on the Human Gut Microbiota

Turnbaugh and colleagues (2009b) conducted an extensive set of diet shift comparisons using a “humanized” mouse model, that is, an initially germ-free mouse that was colonized with a human microbiome. They compared 16S rRNA sequences in humanized mice that were fed conventional mouse chow versus humanized mice fed a “Western” diet (i.e., high fat) and observed a rapid effect of diet shift on the gut microbiome, with only a single day of a high-fat diet having a significant effect. According to Turnbaugh, the results suggest that at least in the mouse model, the gut microbiome is “incredibly dynamic” and can respond to dietary perturbations very quickly. The researchers also found a significant effect of host diet on microbial gene abundance and expression.

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