[PHNUTR-L] Gut microbes' partnership helps body extract energy from food, store it as fat

[Kathrynne Holden, MS, RD]

Colleagues, the following is FYI and does not necessarily reflect my own
opinion. I have no further knowledge of the topic. If you do not wish to
receive these posts, set your email filter to filter out any messages
coming from   @nutritionucanlivewith.com    and the program will remove
anything coming from me.
---------------------------------------------------------
Public release date: 12-Jun-2006
http://www.eurekalert.org/pub_releases/2006-06/wuso-gmp060906.php

Contact: Michael C. Purdy
purdym at wustl.edu
314-286-0122
Washington University School of Medicine

Gut microbes' partnership helps body extract energy from food, store it 
as fat

St. Louis, June 9, 2006 -- Researchers studying mutually beneficial 
interactions between members of our vast community of friendly gut 
microorganisms have shown that two common organisms collude and 
collaborate to increase the amount of calories harvested from a class of 
carbohydrates found in food sweeteners.

In the study, conducted in previously germ-free mice, colonization with 
two prominent human gut microbes led to fatter mice. Scientists at 
Washington University School of Medicine in St. Louis called the results 
an illustration of how understanding the menagerie of microorganisms 
that live in our guts can provide new insights into health. The study is 
will be published online by the Proceedings of the National Academy of 
Sciences.

To one day consider manipulating gut microbes for medical benefits, such 
as weight loss or gain, scientists need to know who's living in our 
digestive systems and how they form strategic alliances with one another 
to benefit themselves and us. They also have to learn how much this cast 
of microbial characters varies in different human individuals.

"We are superorganisms containing a mixture of not just human cells but 
also bacterial cells and cells of another microscopic domain of life 
known as Archaea," says senior author Jeffrey Gordon, M.D., the Dr. 
Robert J. Glaser Distinguished University Professor. "As adults, the 
number of these bacterial and archaeal microbial cells exceeds the 
number of our human cells by tenfold. The genes present in this 
community of 10-100 trillion bugs vastly outnumber our own genes and are 
a key part of our genetic landscape, providing us with attributes we 
have not had to evolve on our own."

One such attribute is the ability to digest commonly consumed complex 
sugars known as polysaccharides. Many types of polysaccharides pass 
through the small intestine mostly unchanged because our human genome 
does not have the genes needed to digest them. Bacterial partners living 
in our colons, such as Bacteroides thetaiotaomicron, begin a 
fermentation process that breaks down these nutrients so that the stored 
calories can be liberated and absorbed.

But B. thetaiotaomicron doesn't just work in a simple partnership with 
its host. The human gut contains hundreds, and perhaps thousands, of 
different microbial species, and the functions they perform affect each 
other and their hosts.

Gordon's lab models the interactions between friendly gut microbes and 
their hosts using gnotobiotic mice. These mice are raised in a manner 
that keeps them germ-free. They are then colonized with one or more 
human gut-derived microbes to study how microbial-microbial and 
microbial-host interactions affect digestive health.

Buck Samuel, a doctoral student in Gordon's lab, began to probe the 
influence of Methanobrevibacter smithii, an archaeon. Originally 
identified in the 1970s and mistaken for a primitive form of bacteria, 
archaea initially became famous because of their ability to live in 
extreme environments where nothing else could survive, such as hot 
springs. Scientists first isolated archaea from the human intestine in 
1982, and have recently recognized M. smithii as the most common 
archaeon in human intestines.

In addition to its prevalence, M. smithii was an intriguing target for 
study because of its ability to consume hydrogen and other byproducts of 
bacterial digestion of polysaccharides. Accumulation of such byproducts 
slows polysaccharide digestion. Samuel and Gordon speculated that M. 
smithii could improve the overall efficiency of digestion of dietary 
polysaccharides, and wondered whether it also affected which types of 
polysaccharides are most coveted by intestinal bacteria.

Samuel colonized one group of gnotobiotic mice with the 
polysaccharide-digesting bacterium B. thetaiotaomicron. Another group 
was colonized with M. smithii, while a third group received both B. 
thetaiotaomicron and M. smithii.

The archaeon's presence dramatically affected gene activity in B. 
thetaiotaomicron, shifting its appetite to a more abundant class of 
polysaccharides known as fructans. Commonly found in Western diet, 
fructans are used as food sweeteners. This taste change increased B. 
thetaiotaomicron's ability to produce energy for itself, and to make 
energy available in forms that the mouse could absorb and use.

The result was that mice colonized with both organisms had significantly 
more fat than animals colonized with either microbe alone. M. smithii 
also benefited – thanks to B. thetaioatomicron, it received increased 
amounts of formate, a product of polysaccharide fermentation that it 
covets and uses.

"The presence M. smithii improved the overall efficiency of the 
digestive system," Gordon says. "It remains to be established whether we 
can intentionally manipulate this gut archaeon to improve digestive 
health. It will also be interesting to see if levels of M. smithii in 
the gut microbial community vary in obese versus lean individuals."

Gordon says the results emphasize the need to consider the nutrient 
value of the foods we consume in the context of the digestive capacity 
of our individual gut microbial communities. To help address such 
questions, Gordon and his colleagues are completing the sequence of the 
M. smithii genome and sequencing the genomes of many other members of 
the normal human gut microbial community. This effort is part of a human 
gut "microbiome" project.

"We believe that this project is a logical extension of the human genome 
project – one designed to define the microbial side of ourselves," 
Gordon says. "This project should help answer a number of fundamental 
questions, including: How different are our individual gut microbiomes? 
How are our gut microbiomes evolving as a function of changes in our 
diet, lifestyle and environment? And can we use this knowledge to 
improve our personal health, including, for example, optimizing the 
performance of our gut microbial communities?"
###
Samuel BS, Gordon JI. A humanized gnotobiotic mouse model of 
host-archaeal-bacterial mutualism. Proceedings of the National Academy 
of Sciences, early online edition.
-- 
Kathrynne Holden, MS, RD < fivestar at nutritionucanlivewith.com >
"Ask the Parkinson Dietitian"  http://www.parkinson.org/
"Eat well, stay well with Parkinson's disease"
"Parkinson's disease: Guidelines for Medical Nutrition Therapy"
http://www.nutritionucanlivewith.com/