Like Hansel and Gretel following a trail of bread crumbs through the forest, we are following some of the stages of microbiome awareness that could eventually lead to astonishing revelations and possibly even some ways to help people maintain normal weight without spending thousands of dollars on gym memberships, special food programs or debilitating operations.
A group of researchers from Massachusetts General Hospital and Harvard University looked at patients who had undergone Roux-en-Y gastric bypass surgery (familiarly known as RYGB) and found changes in their microbial ecology. These modifications were “due to gastrointestinal reconfiguration and not merely due to the associated changes in weight loss, diet, or intestinal transection.”
Their work showed that an altered microbiome could “trigger a reduction in host body weight and adiposity.” These colleagues were very interested in the properties of short-chain fatty acids (SCFAs), which are byproducts of microbial fermentation.
SCFAs feed the cells that line the colon, providing the energy for them to do what they need to do. They also affect the metabolic physiology of the host organism in various other ways. This is one reason why study of the microbiome does not harmonize with a one-size-fits-all paradigm.
Researchers did not know much at this point, but they knew enough to recognize the need for more studies, from several angles of approach, including “surgery, metagenomics, gnotobiotics, and genetic deletions for key metabolic signaling pathways.” Words like this were bandied about:
The human large intestine harbors a complex community of microorganisms (microbiota) that affect many aspects of our physiology and health… Numerous lines of evidence […] have suggested that the intestinal microbiota may play a role in the development of obesity.
Mouse experiments showed that when the microbiota from lean donors are introduced into the intestinal tracts of obese mice, in conjunction with an appropriate diet, weight gain can be reduced. This was a significant discovery, lending hope that similar interventions in humans could achieve the same result. Fecal transplants became a topic of conversation.
Researchers learned that the transplant material does not need to be introduced through the lower end of the intestinal tract, but can be delivered in pill form from above, into the duodenum. It was shown that such an intervention “significantly improves insulin sensitivity” in individuals with metabolic syndrome.
The term “obesogenic bacterial profile” became known as something to avoid, because particular species of microbes love a high-fat diet and use it to create intestinal inflammation and build insulin resistance.
Things got really interesting when it became clear that, bossy as they are, the gut bacteria do not always get their own way, because they are vulnerable to being acted on by the genetics of the host — that’s us.
A very heritable taxon, or group, of bugs, Christensenellaceae, are found in association with a non-obese body. These creatures are even called “the hub of a consortium of co-occurring heritable microbes that are associated with a lean BMI.”
Of course, every discovery brings a new set of questions:
Which specific taxa within the gut microbiome are heritable, and to what extent? Which predicted metagenomic functions are heritable? How do heritable microbes relate to host BMI?
Your responses and feedback are welcome!
Source: “Conserved Shifts in the Gut Microbiota Due to Gastric Bypass Reduce Host Weight and Adiposity,” ScienceMag.org, March 2013
Source: “Fighting Obesity with Bacteria,” ScienceMag.org, Sept. 2013
Source: “Nutrient-Sensing Mechanisms in the Gut as Therapeutic Targets for Diabetes…,” DiabetesJournals.org, September 2013
Source: “Human Genetics Shape the Gut Microbiome,” ScienceDirect.com, 11/06/14
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