A new study published in the
journal Science Translational Medicine suggests that the changes in gut bacteria brought about by gastric bypass surgery may be
the actual reason for rapid weight loss after surgery.
The Roux-en-Y gastric bypass
is the most commonly used bariatric procedure which involves
creating a pouch out of a small portion of the stomach and attaching it
directly to the small intestine, bypassing a large part of the stomach and
duodenum. This way the patient feels less hungry, feels full quickly, burns
more calories at rest and ends up losing most of their excess fat resulting in
improved glucose metabolism.
Scientists believe that these
effects are not just the result of less calorie intake and absorption because
of the surgery and that there is more to it. Earlier studies have shown that
RYGB changes the gut microbiota, but it was not known whether the gut microbes
changed because the patients got thin, or vice versa - the patients got thin
because of changed gut flora.
This led Alice P. Liou at
Obesity, Metabolism & Nutrition Institute and Gastrointestinal Unit,
Massachusetts General Hospital, Boston
, and her colleagues from the same
Institute and also Harvard University, to find out the mechanisms linking
rearrangement of the gastrointestinal tract to these metabolic changes.
In the experiment, a group of obese mice were given the
RYGB procedure. They then transferred the gut microbes from RYGB-treated mice
to non-operated mice. The researchers found that this resulted in weight loss
(5 percent of body weight) and decreased fat mass in these non-operated mice.
They observed that following
surgery, there were increased levels of gut flora, especially, species of Escherichia
. Normally these bacteria are found at relatively
low levels in healthy humans and mice.
The researchers also noticed that
these changes in microbe populations occurred throughout the gastrointestinal
tract, and even far from the site of the surgery, indicating that changes in
the gut flora are not caused by weight loss or caloric restriction, but are
unique to gastric bypass surgery itself.
'Our findings emphasize the
importance of accounting for the influence of the trillions of microbes that
inhabit our body when we consider obesity and other, complex diseases', says
, a postdoctoral researcher at Harvard University and
co-author of the study.
Although not sure how the
microbes cause weight loss, they believe that one of the mechanisms could be
the altered microbial production of short-chain fatty acids.
Their next level of research is
to isolate these microbes and introduce them into obese mice or people.
Antibiotic treatments might help the new bacteria to stick. Despite doubts
expressed by some experts, Lee Kaplan, director of the Obesity, Metabolism
and Nutrition Institute at Massachusetts General Hospital in Boston and another
co-author of this study said, "I believe it's possible".
If confirmed in human studies,
these findings could treat obesity effectively in a non-invasive way.
Reference: A. P. Liou, M. Paziuk,
J.-M. Luevano, S. Machineni, P. J. Turnbaugh, L. M. Kaplan, Conserved Shifts in the Gut Microbiota Due to Gastric
Bypass Reduce Host Weight and Adiposity. Sci. Transl. Med. 5, 178ra41 (2013).