Your body harbors trillions of bacteria that have profound effects on your health, your weight, and even your mood.
There are at least 10,000 different species of bacteria inside your body right now.
Don't bacteria make people sick?
Many of them do, and antibiotics that kill them have saved countless lives. But over the past decade, researchers have discovered that the human body hosts 100 trillion mostly benign bacteria, which help digest food, program the immune system, prevent infection, and even influence mood and behavior. The bacteria living on and in us make up our "microbiome," an ecosystem that plays a role, scientists believe, in many conditions that genes and environmental factors alone can't explain, including obesity, autism, depression, asthma, and even cancer. The discovery of the microbiome, said Michael Fischbach, a bioengineer at the University of California, San Francisco, has been "very much like finding an organ we didn't know we had."
Where is the microbiome?
Bacteria thrive throughout our bodies — in our mouths and lungs, on our skin and teeth, and especially in our guts. The Human Microbiome Project, a government-supported effort to map our bacterial ecosystems, has discovered that people harbor 10 bacterial cells for every human cell. Every body hosts at least 10,000 different species of bacteria, contributing up to five pounds to body weight. "Half of your stool is not leftover food. It is microbial biomass," said project director Lita Proctor. Last year scientists presented evidence that everyone has one of three gut bacterial profiles, or "enterotypes," characterized by high levels of specific bacterial species. Some argue that enterotypes are as distinct as blood types, and that learning more about them will help us design better drugs and target them more effectively.
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