Bears and the Human Microbiome

As many of you know,  I have written extensively over the past several years about the important role of the microbiome. Those 100 trillion organisms that live within the gut, as well as their genetic material, are essential to the body’s regulation and metabolization of food. Notably, this has specific relevance as it relates to obesity.

Previously, I have described how researchers have taken the fecal microbiome from overweight humans, and transplanted it into laboratory mice that specifically lack any gut bacteria (germ-free mice). When germ-free mice are inoculated with the gut bacteria from overweight humans, they begin to gain weight quite dramatically, without any changes to their diet.

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A New Understanding of the Obesity Epidemic

America ranks amongst the highest of all countries in terms of the prevalence of obesity/overweight in its population. No doubt, much of the blame can be placed on the dietary habits that so characterize the American way of life.

While our calorie-rich, nutrient-poor diet is certainly one of the main factors contributing to our growing waistlines, new research indicates that another important issue may be at play causing Americans to pack on the pounds.

Researchers at the Genome Sequencing Center at Washington University have demonstrated that there are remarkable differences in the bacteria living in the intestines of lean humans versus those who are obese. Lean individuals have a higher ratio of a major group of bacteria, Bacteroidetes, when compared to another major group, Firmicutes. The obese subjects in the research project were found to have much higher levels of Firmicutes organisms when compared to the levels of Bacteroidetes.

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Dramatic Weight Gain After Fecal Transplant

We are now learning that differences in the various species of bacteria that live within the intestines actually have a profound role in regulating metabolism. For example, researchers have demonstrated that when fecal material (rich in intestinal bacteria) from an obese human is transplanted into the colon of a normal laboratory rat, the animal will gain significant amounts of weight even though it’s diet remains unchanged.

One explanation for this phenomenon has to do with the idea that certain species of bacteria are actually able to extract more calories from food that is consumed. So transplanting these thrifty bacteria allows the animal to actually obtain a higher calorie delivery to its system, even though the diet wasn’t changed.

In fact, researchers have now characterized the complexion of the gut bacteria in humans associated with obesity in contrast to the gut bacteria found in lean individuals. Obese individuals have higher levels of one large class of bacteria called Firmicutes and lesser amounts of another large group, the Bacteroidetes bacteria. The reverse is true, by and large, in those who are lean.

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