Here's how many tiny bacteria are hanging out in your gut:

Ten sextillion. That's a lot of zeroes.

Researchers are exploring whether a handful of those critters -- a few billion or so -- are making some of us fat.

Even as preliminary clues emerge, however, a Mayo Clinic specialist has some reassuring news about those bugs: "Nearly all of them are friendlies," said Dr. Joseph Murray, a physician and researcher on the digestive system.

Dozens of research projects have begun to probe whether diabetes, depression, skin disorders, autoimmune diseases -- and, yes, obesity -- are at least partly the result of tiny malevolent culprits in your gut. Many of the projects are financed by the National Institutes of Health Human Microbiome Project, launched in 2008 with $115 million.

Leaning on early research, some physicians and nutrition advisers say you can bring joy to the good bugs and discourage the bad ones by getting adequate sleep, controlling stress and eating such foods as unprocessed sugars and grains, garlic, leeks, onions and such fermented foods as yogurt and, yes, sauerkraut.

"Some of that may be true -- or not true, or partly true -- but we just don't know yet," said Murray, whose musical Irish lilt and playful descriptions make you wonder if your stomach perhaps is a pleasant garden filled with happy little leprechauns who seize and boot out the nasty ogres of disease.

Your stomach, he explained, has a thin red line, just one cell thick, that separates the contents from the rest of you.

"Think of it like the movie '300,' kind of a violent movie [about a small band of ancient Spartans trying to stop an invasion of Persians]," he said. This little band of defenders "sends up these tiny periscopes to examine invading bacteria, then sends the bad ones packing -- essentially crowds them out."

For 95 percent of us, that symbiotic relationship works well, "really quite miraculous," Murray said. "We really can't live without all those bugs in our gut. We've shown in mice that we'd have only a primitive immune system without them."

But sometimes the defending bacteria are overwhelmed by invaders, or the good guys change allegiance for reasons not always understood -- perhaps a severe injury, or a separate illness or a change in diet.

The search for bad bugs

In scores of projects, researchers at the University of Maryland and elsewhere are hot on the trail of bacteria, fungi and viruses in the gut that might make people sick.

Some studies, for instance, have found links between some microorganisms and flu in young children, as well as the skin disorder psoriasis and the digestive disorder Crohn's disease.

At the University of Maryland, scientists have identified 26 species of intestinal bacteria connected to high blood pressure, cholesterol and insulin resistance that plague people who are obese -- often precursors to diabetes, strokes and heart disease.

"We can't infer cause or effect," cautioned Dr. Brandi Cantarel, a researcher on the project. "But now that we ... can look at what the bacteria are doing, it can give us more information to go about getting an intervention."

Your bacteria are evolving

Still, it will be some time before gastroenterologists like Murray can regularly prescribe specific foods, or drugs or other treatments to counteract the effects of warring belly bacteria, he said.

"It makes sense to live a good lifestyle -- don't smoke, get good sleep, exercise, eat lots of vegetables and fruits -- but I can't tell you that it will keep those bugs in your belly under control," he said.

Yogurt? Sauerkraut? Onions? They might be good in some cases, but not for people with compromised immune issues such as HIV, Murray said.

"You've got a gut full of bugs that are evolving every time you change your diet or get sick or change your lifestyle. They're there to help you -- but you're also there to make life good for the bugs," he said.

He added: "Just remember, they've got you vastly outnumbered. That's why the cutting edge of research is how to make everybody down there happy."

Warren Wolfe • 612-673-7253