The idea that good health may begin way down deep - all the rage in the early 20th century - is enjoying a scientific revival as microbiologists delve into what may be the human body's final frontier.
It's the colon, or large intestine, the five-foot-long tube that is the last way station in digestion of food in the "gut." Gut, by the way, is a perfectly good scientific term for the digestive system.
A lot more happens way down there than the colon's popular image may suggest. People regard it as a lowly area devoted to recovering water from indigestible material in the diet, and forming packages of waste material that can pass out of the body.
However, the colon does a lot more, thanks partly to an estimated 2.6 pounds of bacteria that live within its twists and turns. Gut bacteria make certain vitamins, for instance, and help teach the immune system to fight harmful microbes that enter the body, and leave the rest alone.
People are born with a sterile, barren colon. Within days, however, it gets populated with bacteria in food and other sources in the environment. By age 2, most of us sport a colon with a thriving population of about 100 different species of bacteria. The mix will remain almost the same until old age.
Gut bacteria live in a complex society, one dependent on another in many different ways. One microbe's waste, for instance, is another's food. They're mixed and matched in precise proportions to discourage dangerous bacteria from horning in.
"Colon health" and "bowel wisdom" were cutting-edge medical technology 100 years ago.
Dr. John H. Kellogg, for example, founded his breakfast cereal empire on it. More than 40,000 patients flocked to Kellogg's Battle Creek, Mich., clinic for colon tune-ups. Kellogg preached health foods that included granola and corn flakes, his first prepared breakfast cereals.
Health foods are behind the modern scientific revival in gut research.
Consumers are buying more than $6 billion worth of "probiotic" and "prebiotic" products each year. Probiotic products, like certain kinds of yogurt and fermented milk, contain living bacteria supposedly good for colon health. Prebiotic dietary supplements contain nutrients that encourage growth of friendly bacteria.
Ads claim that such products strengthen the immune system, counter the bad effects of antibiotics and environmental pollutants, treat certain diseases, and much more.
Governments and other funding agencies are sinking cash into research to test the claims and explore what a January article in the journal Nature describes as a much-neglected research field.
What bacteria live in the gut? Can foods and nutrient supplements tip the balance and improve health? Are probiotics and prebiotics safe? Do some microbes cause colon cancer and other intestinal diseases?
Answers may be years away.
Meanwhile, consumers can educate and amuse themselves with tons of information, junk science, claims, and counter claims about probiotics and prebiotics that litter the Internet. Just search for those words.