A Gut Feeling: New Research Explores the Living Inhabitants of Your Intestines

Obese and lean.

Are you in the market for a healthy, stable, long-term relationship?  Turns out you may not have to look further than your gut.  Or, more specifically, the trillions of microbes that inhabit your gut. Yes, you and a few trillion life-partners are currently involved in a devoted, mutually-beneficial relationship (a trill-some, if you will) that has endured the test of time. Don’t worry though; they’ve already met your mother.

We’re first exposed to our mother’s microbial flora during birth; these are the pioneering settlers of our gastro-intestinal (GI) tract.  In the following weeks our gut becomes fully colonized with a diverse array of bacteria, viruses, and fungi. Although our gut microbes are generally about an order of magnitude smaller in size than human cells, when counted by the trillions, they add up.

In fact, these intestinal interlopers (along with their fellow skin, genital and glandular neighbors) can account for up 2% of a person’s total body mass).  That’s right, a 175lb man could be carrying more than 3 pounds of microbes in and on his body. Most of these microbial tenants, however, are crowded together in the lower part of his large intestine: the colon.
If we travel up the GI tract a bit and inspect the contents of the small intestine, the concentration of microbes drops nearly a billion fold- compared to the colon, it’s practically germ free. Although these germs are harmless when living in the gut, if the intestinal lining is breached, they won’t pass up an opportunity to spread to and wreak havoc in other areas of the body).

While it’s easy to see the lifestyle advantages for a colon-dwelling bacterium (warm food, cozy housing, nearby relatives), the benefits and health implications for humans are not as well understood.  Do we gain anything from toting around these vast microbial populations or are we merely a free meal ticket?

We know from studies in mice that gut microbes can influence health and metabolism. In fact, mice that have been delivered by cesarean section into sterile environments (and therefore lack the usual complement of intestinal microflora) are not as healthy as siblings that are birthed normally. These germ-free rodents have defective GI and immune systems compared to their microbe-ridden brothers and sisters.

While it’s clear that an animal’s gut microbes are a valuable part of a healthy intestine, their role in metabolism and body weight remains ambiguous. We do know, however, that these microbes can enhance digestion, and that an animal’s body weight influences their digestive powers. The gut flora of obese mice, for example, contain a vast array of genes that encode uncommon digestive enzymes.

Normally, anything a mammal cannot digest passes through the GI tract unscathed; the energy present in this food is ‘locked up’, and therefore excreted.  Obese mice, however, hold a few extra keys to calorie consumption.  They are able to break down and extract nutrients from certain indigestible food substances, and, consequently, have fewer calories remaining in their feces than their slimmer relatives.

If obese mice have a different cohort of intestinal bacteria with super-digestive abilities, is the same true of obese humans?  Is there a link between different body types and different gut microbial communities?

Researchers at the Center for Genome Sciences at the Washington University School of Medicine in St. Louis, Missouri are attempting to answer these questions by comparing the identity of these gut community members, or the ‘gut microbiome’, in groups of differently sized people. Recently, Gordon’s lab examined fecal samples from 54 sets of adult female twins (31 of which were identical), and sequenced the DNA of present microbes to describe bacterial lineages and genetic diversity.

Although the majority of the twins selected for the study were identical, nearly every pair of sisters had one drastic physical difference: their body mass index. Gordon’s team of researchers specifically chose twin sets with one obese and one lean member to help understand the role of the gut microbiome in human obesity.

In January 2009, they found of a group of gut microbial genes that were consistently present in the intestines of all the study’s participants. These genes were responsible for encoding several digestive enzymes that help break down sugars and amino acids: useful tools for any humans, regardless of size.

Although most gut microbial genes were shared, a significant portion varied from person-to-person, particularly among the obese and the lean. For instance, the obese member of a twin set generally had a gut microbiome loaded with extra genes involved in fat, carbohydrate, and protein metabolism. Are these mighty microbial metabolizers so efficient at squeezing calories from food that they actually contribute to their landlord’s obesity?  Maybe, but we can’t say for sure just yet.

We do know that our gut is a kind of multi-species digestive super-organ, and that changes in the intestinal microbiome are associated with vastly different body types. In fact, Gordon’s lab has shown that you can actually fatten up a lean mouse by feeding it microbes from the guts of its obese peers. Although it’s still unclear exactly how the organisms in our intestines contribute to obesity, this research provides something for follow-up studies to chew on.  Is it possible, then, to lose weight by feasting on the gut bacteria of a skinny friend?  Perhaps. Just don’t try it at home.

References:
1.     Othman, M., Agüero, R., & Lin, H. C. (2008). Alterations in intestinal microbial flora and human disease. Current Opinion in Gastroenterology, 24(1), 11-6.
2.     Hord, N. G. (2008). Eukaryotic-Microbiota crosstalk: Potential mechanisms for health benefits of prebiotics and probiotics. Annual Review of Nutrition, 28, 215-31.
3.     Bajzer, M and Seeley, RJ (2006, December). Obesity and gut flora. Nature, 444, 1009-1010.
4.     Sekirov, I, and Finlay BB (2006, July). Human and microbe: United we stand. Nature, 2(7), 736-737.
5.     Turnbaugh, P. J., Ley, R. E., Mahowald, M. A., Magrini, V., Mardis, E. R., & Gordon, J.I. (2006). An obesity-associated gut microbiome with increased capacity for energy harvest. Nature, 444(7122), 1027-31.
6.     Ley, R. E., Turnbaugh, P. J., Klein, S., & Gordon, J. I. (2006). Microbial ecology: Human gut microbes associated with obesity. Nature, 444(7122), 1022-3.
7.     Turnbaugh, P. J., Hamady, M., Yatsunenko, T., Cantarel, B. L., Duncan, A., Ley, R.E., et al. (2009). A core gut microbiome in obese and lean twins. Nature, 457(7228),     480-4.

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~ by Meghan on March 13, 2009.

2 Responses to “A Gut Feeling: New Research Explores the Living Inhabitants of Your Intestines”

  1. I want to be a student of you. A junior fellow apprentice of you, I think. I’m a boy,postgraduated degree on Animal Genetics, Breeding and Reproduction. I’m now working in an animal center in China. I’ve got a task of produce germfree mice,rats in the next 10 months. So I’m busing in expolring all kinds of infomations on germfree animal production and gnotobiotic methods.
    I want be a listener of you. I want be a friend of you also.

  2. I think you are good at serveral directions. You can be a adviser of me, a teacher of me. I want learn more about you. My E-mail add: zhaolihu@sina.com. I’m waiting for you reply. Thank you !
    Good night!

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