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Bacteria and Obesity, A Surprising Link

Bacteria and Obesity, A Surprising Link

As a chemical engineer, I am naturally drawn to write columns about energy and manufacturing.  However, if you have been reading my columns for a while you will have noticed that I keep coming back to topics concerning the vital importance of maintaining a healthy population of beneficial bacteria within us, particularly within our gastrointestinal (GI) system.  I did not expect to return to this arena again so soon, but then I learned something new, something amazing.  So here we go again.

First, here are some relevant points of the past columns on this subject along with the associated links.

  • By a wide margin, most of the DNA in our bodies is not our own but rather belongs to our resident bacteria.  With this in mind, it is more accurate to consider our bodies as ecosystems rather than as isolated organisms.
  • When people are treated with antibiotics, their population of healthy GI system bacteria is temporarily reduced.  In some cases, the body is unable re-establish the former healthy bacterial equilibrium leading to debilitating diarrhea and, in extreme cases, death.  Recent studies have shown dramatic improvements for patients suffering from this condition by recolonizing their GI tract with bacteria from a healthy individual through a process known as a fecal transplant.
  • Prior to birth, babies have sterile GI tracts.  To ensure good health, and even survival, newborns must quickly populate their GI tracts with the proper bacteria.  Babies born vaginally ingest fluids from their mothers during birth which contain the necessary beneficial bacteria to colonize their intestines.  Babies born via C-section miss this opportunity and, due to this slow start on GI tract health, develop food allegories at a rate five times higher than babies born vaginally.

These previous columns on importance of bacteria in the GI tract had already piqued my curiosity and then I stumbled upon a new wrinkle to this story, an amazing wrinkle.   A recent study in the International Journal of Obesity (IJO) concluded that use of antibiotics in young children results in reduced diversity of GI tract bacteria for sustained periods of time.  This was not particularly surprising.  The noteworthy portion of the IJO study was that these children gained weight at increased rates and maintained higher body weights into adulthood. When I read the abstract for this study, I had the sensation of having the fog lifted from my brain and a whole series of ideas and concepts suddenly crystallized for me.  An “Aha!” moment, so to speak.

First it struck me that people are just like cows, pigs, and chickens.  For the past half century or so farmers have been feeding antibiotics to their livestock from the day they are born.  For reasons that have not been entirely clear, this practice results in dramatically increased rates of weight gain and much larger overall size.  The IJO study strongly suggests that same mechanism is operative in humans, feed them antibiotics, particularly at a very young age, and they gain weight faster and become larger.  This analogy between livestock and humans is not much of a reach.  However, in all of the discussions regarding increased rates of obesity in the United States I have not encountered any suggestion that increased antibiotic use was a possible root cause.

Next I thought about people who to seem to be able to eat a tremendous number of calories but don’t ever gain weight.  The popular view is that these people have a “fast metabolism”.   As an engineer, I have never been able to accept this explanation as the implied heat and energy balance doesn’t really work.   While there are some differences in people’s metabolic rates (calorie consumption at rest) they are not large enough to explain why my friend Chris 1 who, after a large meal at a Chinese Buffet often eats a large pizza for desert, has almost no body fat. (I’m not exaggerating, I promise.) If someone’s metabolic rate was high enough to expend this many calories, even while just sitting around, their skin would heat up and they would start to sweat.  Chris isn’t particularly sweaty. The fascinating implication of the IJO study is that Chris likely has a population of bacteria in his GI tract that limits his ability to gain weight even when he eats prodigious amounts of food.

So let’s take what we know about bacteria in the GI tract so far and extrapolate a little.  We already know from the fecal transplant experiments that we can colonize person A’s GI tract with bacteria from person B.   This suggests that if I can take bacteria from someone with a “high metabolism” like Chris and transplant it into the intestines of someone who seems to carry excess pounds no matter what, that he/she may become thin and stay that way.  Given the staggering amount of money currently expended on diet plans and weight loss pills, a simple bacterial transplant procedure which induces sustainable weight loss could be the invention of the century.

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(1)    I have omitted Chris’ last name so people don’t start chasing him down the street demanding a bacterial sample.

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