SUSUMU NISHINAGA/SCIENCE PHOTO LIBRARY
Hard Science

Bacteria Cells in Our Bodies Do Not Outnumber Human Cells by 10 to One

June JavelosaJanuary 12th 2016
News
SUSUMU NISHINAGA/SCIENCE PHOTO LIBRARY
Microbiota

People have long said that, in the human body, there are more bacterial and microbial cells than human. According to TedTalks, and scientific papers, and blog articles, bacteria outnumber our own cells ten to one. In fact, that’s something that we’ve even stated before. (You can see the article here; we were reporting from a study published by Harvard, CalTech and the National Institutes of Health).

However, according to new research, which was conducted by scientists from Canada and Israel, that’s not quite true. Actually, it’s off by a lot. The ratio is more likely one to one.

1024px-Human_Paneth_cells
Human Paneth cells via WikiMedia

Using a 70 kilogram man, anywhere from 20-30 years old and 1.7 meters tall as a reference, they explain that this individual should contain about 30 trillion human cells and 39 trillion bacteria. However, that said, these numbers are approximations. Obviously, we can’t go in and count every, single cell. As such, it’s likely that another person may have twice as many bacteria or even half as much.

Still, it’s very far from the purported 10 to 1 ratio commonly believed.

So, where did the myth come from?

The propagation of the myth dates as far back as the 70s, when a microbiologist by the name of Thomas Luckey gave his estimate. He asserted that there are 100 billion microbes in a gram of human intestinal fluid, and since there are about 1,000 grams of these materials in the average adult, that equals a total of 100 trillion microbes.

The researchers note that while Luckey’s assertions were “elegantly performed,” he was probably never “meant to be quoted decades later.” Rather, he was relying on the best estimates at the time, and the updated research just never came. Until now.

By 2014, molecular biologist Judah Rosner from the US National Institutes of Health at Bethesday began to question the veracity of Luckey’s estimate, within the context that there were very few good estimates given for the numbers of human and microbial cells in the body.

To that end, researchers are now reestimating the number based on a review of the latest experimental data in literature, including DNA analyses that help calculate cell number and magnetic resonance imaging to calculate organ volume. Despite the better (and, presumably, more accurate estimate), some scientists still think that it won’t have any biological significance. We are made up of lots of bacterial cells, just how much doesn’t really signify.

The paper is currently being reviewed for publication in a scientific journal.

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