Gross of note:

Scientists have long known that at least 50 percent of human feces, and often more, is made up of bacteria from the gut. Bacteria start to colonize the intestines and colon shortly after birth, and adults carry up to 100 trillion microbes, representing more than 1,000 different species.

They are not just freeloading. They help humans to digest much of what we eat, including some vitamins, sugars, and fiber. They also synthesize vitamins that people cannot.

We are not entirely human, germ gene experts argue
Thu Jun 1, 2006 02:13 PM ET
By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - We may not be entirely human, gene experts said on Thursday after studying the DNA of hundreds of different kinds of bacteria in the human gut.

Bacteria are so important to key functions such as digestion and the immune system that we may be truly symbiotic organisms -- relying on one another for life itself, the scientists write in Friday's issue of the journal Science.

Their findings suggest that studying bacteria native to our bodies may provide important clues to disease, nutrition, obesity and how well drugs will work in individuals, said the team at The Institute for Genomic Research, commonly known as TIGR, in Maryland.

"We are somehow like an amalgam, a mix of bacteria and human cells. There are some estimates that say 90 percent of the cells on our body are actually bacteria," Steven Gill, a molecular biologist formerly at TIGR and now at the State University of New York in Buffalo, said in a telephone interview.

"We're entirely dependent on this microbial population for our well-being. A shift within this population, often leading to the absence or presence of beneficial microbes, can trigger defects in metabolism and development of diseases such as inflammatory bowel disease."