Microbiomes and Health

The human body is home to trillions of tiny living things—bacteria and other microbes—that live on our skin and, especially, deep inside our digestive systems. Together, this vast and varied community is known as the microbiome. Far from being merely harmful germs that ought to be wiped out, many of these microbes are now understood to be genuinely essential to our health. In fact, the relationship between human beings and these countless microbes is now best described as a kind of （ 1 ）, in which both sides benefit.

These microbes do far more than was once realized. They help us to digest our food and to produce certain vitamins, and they play an important part in training the immune system to tell genuinely harmful invaders apart from harmless ones. Some research has even begun to link the microbiome to mood and behavior, through chemical signals that travel between the gut and the brain. What we choose to eat strongly affects which microbes thrive inside us, which is one important reason why a varied diet, rich in plants, is so （ 2 ） for many different aspects of our health.

Because of exciting discoveries like these, the microbiome has rapidly become a thrilling area of medical research, with real hopes that it might one day be deliberately adjusted in order to treat disease. Yet scientists are careful to urge caution. The microbiome is enormously complex, and a great deal about it still remains poorly understood. （ 3 ） all the excitement, reliable treatments based on the microbiome are still mostly a matter for the future, and simple, confident claims about "good bacteria" should be treated with real care.