Mayo Clinic Proceedings Examines a Possible Link Between Bacteria Found in the Human Digestive System and Obesity

ROCHESTER, Minn., April 1, 2008 /PRNewswire-USNewswire/ -- Obesity is
more than a cosmetic concern because it increases a person's risk for
developing high blood pressure, diabetes and many other serious health
problems. It's well understood that consuming more calories than you expend
through exercise and daily activities causes weight gain. But with about
one in every three American adults now considered obese, researchers are
attempting to identify additional factors that affect a person's tendency
to gain and retain excess weight. In the April issue of Mayo Clinic
Proceedings, researchers from Mayo Clinic Arizona and Arizona State
University examine the role that bacteria in the human gastrointestinal
tract play in regulating weight and the development of obesity.



Known as gut microbiota, the trillions of bacteria that populate the
human gastrointestinal tract perform a variety of chores. These "friendly"
microbes help extract calories from what we eat, help store these calories
for later use, and provide energy and nutrients for the production of new
bacteria to continue this work.



According to John DiBaise, M.D., a Mayo Clinic Arizona
gastroenterologist and lead author of the Mayo Clinic Proceedings article,
several animal studies suggest that gut microbiota are involved in
regulating weight and that modifying these bacteria could one day be a
treatment option for obesity.



One study cited by the authors observed that young,
conventionally-reared mice have a significantly higher body fat content
than a laboratory-bred, germ-free strain of mice that lack these bacteria,
even though they consumed less food than their germ-free counterparts. When
the same research group transplanted gut microbiota from normal mice into
germ-free mice, the germ-free mice experienced a 60 percent increase in
body fat within two weeks, without any increase in food consumption or
obvious differences in energy expenditure.



Another animal study reviewed by the authors focused on the gene
content of the gut microbiota in mice. Finding more end products of
fermentation and fewer calories in the feces of obese mice led researchers
to speculate that the gut microbiota in the obese mice help extract
additional calories from ingested food.



"These results suggest that differences exist in the gut microbiota of
obese versus lean mice, raising the possibility that the manipulation of
gut microbiota could be a useful strategy for regulating energy balance in
obese people," says Dr. DiBaise.



Although information on the link between gut microbiota and obesity in
human subjects is more limited, the authors present some evidence
supporting this connection. One study cited placed 12 obese participants in
a weight-loss program for a year, randomly assigning them to either a
fat-restricted or carbohydrate-restricted, low-calorie diet. Researchers
noted distinct differences between lean and obese participants when they
monitored the type and number of bacteria found in participants' stool
samples before and after the diet changes.



Another study cited followed children from birth to age 7 and analyzed
stool samples collected at 6 and 12 months. The children who were normal
weight at age 7 had distinctly different bacteria in their samples from
those collected from overweight-obese children, suggesting that differences
in the composition of the gut microbiota precede overweight-obesity.



Dr. DiBaise says that much more research is needed to clarify a number
of issues related to the relationship between the gut microbiota and
obesity. Future studies need to establish whether the small changes in
caloric extraction seen in recent studies can produce measurable weight
differences in humans. Second, researchers need to prove or disprove the
possible relationship between the gut microbiota and the regulation of
weight.



"In particular, it is essential to demonstrate unequivocally whether
differences in gut microbiota in obese versus lean people are the cause or
the result of obesity," says Dr. DiBaise.



Finally, the authors note that the next wave of research should explore
the safety and feasibility of modifying the gut microbiota in clinical
trials involving humans.



"Although clearly no substitute for proper diet and exercise,
manipulation of the gut microbiota may represent a novel approach for
treating obesity that has few adverse effects," says Dr. DiBaise.



Other authors of this article include: Husen Zhang, Ph.D., Rosa
Krajmalnik-Brown, Ph.D., and Bruce Rittmann, Ph.D., from Arizona State
University; and Mayo Clinic Arizona researchers Michael Crowell, Ph.D. and
G. Anton Decker, M.B.B.Ch.



A peer-reviewed journal, Mayo Clinic Proceedings publishes original
articles, reviews and editorials dealing with clinical and laboratory
medicine, clinical research, basic science research and clinical
epidemiology. Mayo Clinic Proceedings is published monthly by Mayo
Foundation for Medical Education and Research as part of its commitment to
the medical education of physicians. The journal has been published for
more than 80 years and has a circulation of 130,000 nationally and
internationally. Articles are available online at
http://www.mayoclinicproceedings.com.



To obtain the latest news releases from Mayo Clinic, go to
http://www.mayoclinic.org/news. MayoClinic.com (http://www.mayoclinic.com) is available
as a resource for your health stories.











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Via: Healthcare