I just heard a very interesting talk from Dr. Liping Zhao, who is
Director of the Laboratory of Molecular Microbial Ecology and
Ecogenomics, and Associate Dean of School of Life Sciences and
Biotechnology, at Shanghai Jiao Tong University. He is also associated
with the new Shanghai Center for System Biomedicine. He described a
consistent effect of diet (high fat vs. normal or normal vs. low fat)
and caloric restriction on the composition of mouse gut microflora. I
was impressed that even within a treatment, the composition of gut
microflora was an indicator of lifespan. This correlation is
interpreted by him in terms of a cumulative effect of anergy on health.
His working hypothesis is that excess calories feed gut bacteria that
cause inflammation, leading to a variety of health problems. A freely
available paper from his group was published in PNAS in 2008 ("Symbiotic gut
microbes modulate human metabolic phenotypes"). I expect that the
results that he presented today will be published somewhere soon, and
we're certain to see a lot more about the gut microbiome and health in
the years to come.

http://ifdiet.blogspot.com/2010/11/liping-zhao-on-caloric-restriction-gut.html