New research provides stronger evidence that the composition of gut
bacteria influences obesity.
Three new studies involving mice and humans provide new and stronger
evidence that the composition of gut bacteria influences obesity.
In a U.S. study, fecal material from four human twin pairs (each set
included one obese and one lean twin) was transplanted into
genetically identical mice that were raised in a germ-free
environment. The mice that received gut microbiota from obese humans
became obese and developed obesity-related metabolism traits:
dyslipidemia, insulin resistance, and inflammatory markers. In
contrast, mice that received microbiota from lean humans stayed lean.
Because mice routinely eat each other’s feces, researchers tried
housing obese mice with lean mice — the obese mice gradually became
lean and lost the obesity-related metabolic changes, and their gut
flora changed to resemble that of the lean mice.
In a study from France, researchers compared genes from the gut
microbiomes of 123 nonobese and 169 obese humans. The nonobese humans
typically exhibited a different composition of gut bacteria, although
the differences involved just a few species. Certain bacterial species
were linked to insulin resistance, fatty liver, and inflammation. In
another French study, investigators found the same “obesity-
related” bacteria to be present in their 49 obese participants,
particularly those with obesity-related metabolism traits. When
participants were placed on energy-restricted diets for 6 weeks, their
microbiome changed toward that seen in lean individuals. Returning to
their typical diets for 6 weeks moved the participants’ microbiomes
back toward the initial composition.
Collectively, these three studies provide strong evidence that the
composition of bacteria in our gut affects whether we are obese — and
whether we develop obesity-related metabolism traits. They also
indicate that what we eat can affect our microbiome. The studies do
not prove that the gut microbiome will predict which people will
become obese or develop obesity-related metabolism. And they surely
don’t prove that directly altering the gut microbiome of obese people
will improve their health. However, many investigators already are
interested in pursuing those possibilities.
Ridaura VK et al. Science 2013 Sep 6. Le Chatelier E et al. Nature 2013 Aug 29. Cotillard A et al. Nature 2013 Aug 29.