The Three Pound Alien In You

The latest New Yorker (10/22/12) has a fascinating article on your microbiome, the roughly three pounds of bacteria that roam your body. (You have approximately 10,000 different organisms, all together weighing as much as your brain.) Only subscribers can read the whole piece online, but you will find a short abstract here.

Researchers have realized that the bugs we have been killing off with such zest are fundamentally part of our system, sometimes doing good and sometimes doing bad. They are like an extra organ, just discovered. For example, there’s evidence that microbial populations help us keep our weight down by controlling our appetite–that’s probably why farmers feed antibiotics to pigs and find that they gain weight faster. The widespread use of antibiotics in children may be the reason for the epidemic of obesity, the article suggests, not the size of the colas available. Antibiotic use may also be linked to the dramatic rise in asthma. And who knows what else.

It makes sense: if you have ten thousand species weighing three pounds swimming around in you for your entire life, their interactions would have to be complicated. (If you had a three-pound cat sitting on your head, those interactions would be complicated too.)

Where do you get your microbiome? Mostly at birth, from your mother’s vagina. Those who are born by C-section don’t get nearly all the bugs, which may explain why C-section children can have special health issues.

With the increase in C-sections, and the greatly increased use of antibiotics, there seems to be a serious downward trend in the organisms, generation by generation. That could spell serious trouble. We don’t really know, because research into the microbiome is just in its infancy. We do know this: medicine just got more complicated.


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One Response to “The Three Pound Alien In You”

  1. David Graham Says:

    As someone who has done plenty of c-sections, I can say that I haven’t seen any special long term health issues for babies born this way. There was indeed an isolated study from the British Medical Journal in May of this year which showed that for their particular study, carried out in one city in North America for only three years, there was an association between children born by C-section and higher rates of obesity at the age of 3.

    But “association” is not the same thing as “cause-effect.” Obesity at age 3 – after three years of feeding – is hardly a definitive pronouncement about c-section causing obesity. Moreover, the vast majority of children born by c-section had NOT developed obesity. Which is a good reminder that one study doth not a truth make.

    Many of the organisms that come to colonize our bodies as babies are things we pick up ourselves. Babies put just about anything in their mouths – a mother’s breast, her milk, food, anything left on the floor, their hands – so there are plenty of other sources for picking up microbes beside the mother’s vagina.

    On the issue of microbiomes, I am reminded of the passage in David Attenborough’s “The Trials of Life” (p. 184) that describes how we animals, as individuals, are really more like communities. “Most large animals, in fact, are not the single individuals them seem to be. They are walking menageries, whole communities of different species.”

    He wrote this after describing a buffalo standing in a swamp stolidly chewing the cud. “Oxpeckers cling to its flanks. Ticks are boring into its hide. Leeches may have fastened on to it when it went to drink and now lie within its mouth attached to its lips. Tapeworms, hidden from view, may be trailing through its convoluted gut, roundworms encysted in its muscles and flukes moored in the veins of its liver absorbing its blood. All these creatures are robbing it of sustenance. But there are still others, even smaller, which are providing it with food and without these it would starve. Microscopic organisms are swarming in the compartments of its stomach, helping it to break down the cellulose in the plants that it has eaten which otherwise it could not digest.”

    All of which is to say that the relationships big organisms have with small organisms who take up residence in them is a fascinating field of study, still in its infancy, as you correctly noted.

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