A disruptive element such as a change in diet, and
the whole intestinal flora becomes disrupted, with
possible repercussions for health.
An international research study conducted by the
Molecular Microbial Pathogenesis Unit (Institut
Pasteur/Inserm), directed by Philippe Sansonetti,
has just demonstrated, in mice, the direct influence
of a diet too high in fat on the intestinal flora
and its environment.
In response to this new diet, the bacterial
communities reorganise themselves and the small
intestine itself is transformed. And this happens in
the first month. These results were published in the
The billions of bacteria that populate our intestine
– known as the microbiota – play a central role in
digestion, but also have a role in some diseases
such as type 2 diabetes or obesity.
Some diseases such as type 2 diabetes or obesity
have often been associated with an imbalance of the
intestinal flora, with some bacteria becoming
clearly predominant, and a permeable intestine,
likely to release inflammatory substances into the
Some mice in a new study were fed an ordinary diet,
whereas others were fed a diet containing 70% lipid.
Using genomic techniques, the researchers were able
to identify the different bacterial species
contained in faecal samples, and monitor the changes
in composition of the microbiota in time.
They also localised and accurately identified the
bacteria within the small intestine.
“Only one month after starting this new high-fat
diet, we observed changes in the composition of the
microbiota,” says Thierry Pédron, a research
engineer in the Molecular Microbial Pathogenesis
Unit (Institut Pasteur/Inserm).
“Some bacterial species proliferated, whereas others
declined, and the species Candidatus arthromitus
actually disappeared completely.
Furthermore, and as never seen before, we observed a
massive concentration of bacteria between the
Ordinarily, bacteria cannot come close to or even
cross the intestinal wall because the epithelium
releases antimicrobial peptides and is lined with a
The researchers then focused on these intestinal
wall defences: they found that production of
antimicrobial peptides fell following massive
ingestion of fat, and that the mucus layer became
In other words, not only does the microbiota become
reorganised under the influence of lipids, but the
intestine itself undergoes transformation.
And the modifications do not end there.
Additional measurements made it possible to
demonstrate an increase in the permeability of the
small intestine, and a reduction in PPAR-? activity.
“PPAR-? is a molecule with many functions. It plays
an important role in fatty acid metabolism, as well
as in inflammation and embryonic development,”
explains Thierry Pédron.
“This drop seems closely related to the drop in
antimicrobial peptide level.”
And although the connections between all these
results and their potential involvement in some
dietary imbalances have not yet been established, it
is reassuring to note that when the mice are put
back on a balanced diet, everything returns to
normal within a month!
For more information
PNAS - Proceedings of the National Accademy of
Sciences of the United States of America
High-fat diet modifies the PPAR-? pathway leading to
disruption of microbial and physiological ecosystem
in murine small intestine
Institut National de la santé et de la recherche