The Human Microbiota and Obesity

As technology advances our ability to examine the populations of microbes, or microbiota, living on or in our bodies, interesting trends  are emerging from the data. With American obesity rates rising to over 34%, scientists are beginning to pay more attention to the role of microbes in digestion. The communities of microorganisms living inside our bodies are referred to as the microbiota.  Weighing in at 3 lbs, the gut flora (the microbiota of the human digestive tract specifically) are regarded by many as a bacterial organ. They take part in everything from immune response to vitamin production, but their role in nutrient absorption is especially relevant when talking about obesity.

The Department of Internal Medicine at the University of Campinas found that germ-free mice are more resistant to weight gain than those with bacteria. This is not to say that the total volume of bacteria is what is important, though. Different ratios of bacteria have different effects on weight gain. For example, obese mice were shown to have a smaller proportion of Bacteroidetes to Firmicutes relative to lean mice.Graphic of mice with different bacteria

Scientists observed that the bacteria in obese mice produced special enzymes to extract energy from complex sugars (a.k.a. polysaccharides).  With microbes breaking down previously unavailable sugar, they may possibly increase the amount of energy that an individual absorbs from their food. From a survival standpoint this is a productive mechanism, but for most people battling their waist lines, a little less efficiency is in order and a higher percentage of Bacteriodetes in their intestinal microbiota would be more beneficial.

There are lots of questions that still need to be answered. Though the effects of enhanced polysaccharide digestion alone bear little impact on weight gain, it seems to be a part of a larger phenomena. In obese people, the presence of more Firmicutes appears to increase the number of calories absorbed in general. Scientists are not certain how bacteria are able to do this, but they believe it has something to do with intestinal inflammation triggered by high fat diets. At any rate, the old adage about a calorie being a calorie simply does not do the body’s complexity justice.

Maybe weight loss calculators of the future will ask for your bacterial ratios in addition to daily activity levels. Until then, “calories in versus calories out” should be taken with a grain of salt.

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Photo Credits

Obese Mouse vs. Thin Mouse graphic: Ricochet Creative Productions

Photo of 2 Mice: Public Domain via WikiMedia Commons

Kim Scott is a sophomore at Western Carolina University where she is studying for a career in nursing. Kim is also one of the instructional designers at Ricochet Creative Productions.

This article was updated on Aug 21st with a new reference to the NPR article  – Does this Phylum Make Me Look Fat?

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