Your body is teeming with bacteria, fungi, viruses, and other microbes that together make up your microbial inner ecosystem, or microflora. Your body actually contains about 100 trillion cells, but amazingly only one in 10 is “human.” The others are made up of bacteria and other microorganisms.

As reported by Quartz:¹

“Bacterial cells alone outnumber our own by a factor of 20. No one has estimated the number of viruses, but we expect between ten and a hundred times more than the bacteria. In the body, microbial genes outnumber human genes by a factor of 200.”

You may recall the Human Genome Project, which was launched in 1990 and completed in 2003.² The mission was to map out all human genes and their interactions, which would than serve as the basis for curing virtually any disease.

Unfortunately, not only did they realize the human body consists of far fewer genes than previously believed, they also discovered that these genes do not operate as previously predicted. Part of the problem is that we are not simply a product of our human cells – we’re a product of our microbiome as well.

Your genes, in fact, can be influenced by the bacteria and other microbes in your body, so by studying the microbial makeup of any population, you can actually gain much insight into its health. This is just what one group of researchers set out to do, using easily one of the best sources of human microbes around… poop.

City Sewage Reveals Communities’ Obesity Rate

Researchers from the University of Wisconsin and the Marine Biological Laboratory in Massachusetts analyzed more than 200 sewage samples from treatment plants in 71 cities. Using genetic sequencing, they determined that about 15 percent of the bacteria tested came from human feces.³

Testing of gut microbiomes among individuals has to date shown that each is highly individual, with no core set of bacterial species dominating. However, by sampling sewage, which gives access to samples from millions of people, much less variability was present.

The researchers identified a set of “core” bacteria (about 60 types in all) that they noted are “both common to and abundant in the US populations.” Still, there were noted differences from city to city. As reported by the American Association for the Advancement of Science:⁴

“…the abundance of these and less common bacteria varied from place to place. This variation in the “sewer-wide” microbiomes reflected the variation seen among surveys of microbiomes of individual people. Each city had “a unique signature,” [Sandra] McLellan [a microbiologist at the University of Wisconsin] explains.

Those differences offer hints about the health of cities’ residents. Fat people tend to have a different microbiome from that of lean people, for example.

By analyzing the microbes in each city’s sewage, the researchers could tell which had an obesity problem, [Mithcell] Sogin [a molecular evolutionist at the Marine Biological Laboratory] says.

Denver and Key West, Florida, microbes reflected a leaner population than those from Salina, Kansas, and Memphis, Tennessee, for example.”

In fact, by analyzing the distribution patterns of different groups of microbes, the researchers were able to determine whether the sewage samples came from obese or lean populations, with up to 89 percent accuracy.⁵