An article in the NY times about microbes and their interaction with our bodies contained the following statement:
We have over 10 times more microbes than human cells in our bodies
I'm a bit skeptical about that statement. It compares microbes to human cells, but since the article describes DNA analysis methods to describe our microbiome, is the statement really about genetic material and not cell number? Where can I find additional material on this subject?
This is from Elizabeth Pennisi (Science Magazine, 2010)
This past decade has seen a shift in how we see the microbes and viruses in and on our bodies. There is increasing acceptance that they are us, and for good reason. Nine in 10 of the cells in the body are microbial. In the gut alone, as many as 1000 species bring to the body 100 times as many genes as our own DNA carries.
Their genes and ours make up a metagenome that keeps the body functioning. This past decade we’ve begun to see how microbial genes affect how much energy we absorb from our foods and how microbes and viruses help to prime the immune system.
The ideas of a microbiome and a virome didn’t even exist a decade ago. But now researchers have reason to hope they may one day manipulate the body’s viral and microbial inhabitants to improve health and fight sickness.
From Discover Magazine (2011)
There are 20 times as many of these microbes as there are cells in the body, up to 200 trillion in an adult, and each of us hosts at least 1,000 different species.
... a person is not so much an individual human body as a superorganism made up of diverse ecosystems, each teeming with microscopic creatures that are essential to our well-being.
Two of the largest efforts [to use genetic sequencing to explore how the diversity of the microbiome impacts our health] are the Human Microbiome Project, funded by the National Institutes of Health, and the European Union’s Metagenomics of the Human Intestinal Tract.
Although these groups have only just begun to publish their findings, it is already clear that the microbiome is much more complex and very likely more critical to human health than anyone suspected.
To clarify a possible point of confusion, microbial biomass is only a small portion of a human body's mass, due to the small size of bacterial cells relative to human cells.
From San Francisco Chronicle (2012):
The human body carries more than 100 trillion bacteria - up to five pounds of the tiny >single-celled organisms.
No, we do not.
Although this figure is widely cited (as per Oliver_C's answer), it is based on rather old data (paywalled, unfortunately), and these estimates are now thought to be inaccurate. A recent estimate by Sender, Fuchs, and Milo puts it at a close to one-to-one ratio of human to microbial cells:
Our analysis updates the widely-cited 10:1 ratio, showing that the number of bacteria in our bodies is actually of the same order as the number of human cells. Indeed, the numbers are similar enough that each defecation event may flip the ratio to favor human cells over bacteria.
Less dense articles reporting these findings can be read here and here (Nature).
