4 habits for a healthy gut

Essentially, the gut is your body's gatekeeper, letting in helpful compounds and evicting harmful ones. It's home to 70 to 80% of our immune cells. When the gut is in good shape, our systems run efficiently, but when it's not, we may experience upset stomach, be at risk for weight gain or digestive problems like heartburn and constipation, or just feel vaguely out of sorts.

For many people, that run-down feeling has lasted so long that it's mistaken for the norm, says New York cardiologist Alejandro Junger, author of "Clean Gut."

"We could feel so much better -- we just don't know it."

The gut is swarming with about 100 trillion bacteria, or flora, which outnumber human cells in our body 10 to 1. Bacteria are often considered "good" or "bad."

"These bacteria and the compounds they excrete can have positive and negative effects on a person's health," says Dr. Stanley Hazen, chair of cellular and molecular medicine at the Cleveland Clinic. "To have a healthy gut, one must avoid eating foods that foster the growth of bacteria that create unhealthy metabolites."

Friendly bacteria aid the metabolism of nutrients and help certain compounds get into the bloodstream. A diverse population of health-promoting flora protects the gut from the less helpful strains.

In contrast, an outsize number of less-beneficial flora -- which proliferate with a diet high in sugar, fat, and processed food -- can cause gas, discomfort, bloating and inflammation. The flora can also emit chemicals that compromise the intestinal lining, says Lita Proctor, of the Human Microbiome Project at the National Institutes of Health.

"This so-called 'leaky gut' allows nonnutritive materials to slip into our bodies and affect how we feel."

Incredibly, some bacteria might even make you fat: A recent study of twins, published in "Nature," found that when bacteria from an obese human twin were introduced into the digestive systems of lean mice, the mice turned fat; when bacteria from the thin sibling were introduced into lean mice, the mice stayed lean. Studies also suggest that diabetic and obese patients tend to lack a diversity of bacteria, and the Cleveland Clinic found that some bacteria metabolize components of egg and meat to produce a compound that aids in the clogging of arteries.

"This might explain why some unhealthy eaters get heart disease while others don't," says Hazen.

The good news is that you can reset your gut bacteria, swapping bad flora for good.

"Get the right type in your gut and, depending on your condition, you may begin to see improvements in a matter of days or weeks," says Edmond Huang, a metabolic biologist at the University of California, Berkeley.

To cultivate healthful microflora, you want to nourish the desirable species while killing off the bad. Beware of antibiotics, however, which decimate the flora keeping our bodies healthy along with those causing illness and infection.

"Every course of antibiotics has a chance for such complications as yeast infections, skin rashes, and allergic reactions," says Liponis.

Use these drugs only when needed, and always supplement with probiotics to repopulate the healthful flora.

Probiotics -- the good bacteria in fermented foods and supplements -- bolster the number of friendly bacteria in the gut. For relatively healthy people, it's always a good idea to start with real food before taking supplements.

Bifidobacteria, found in most yogurt, release chemicals that create an acidic environment in which many harmful bacteria can't thrive. And yogurt with the common strain Lactobacillus rhamnosus may improve your mood: A 2013 study published in "Gastroenterology" found that when healthy women ate 125 grams of yogurt twice daily for four weeks, their brain scans showed a less intense response when exposed to negative images.

You can nourish healthful flora with prebiotics, which contain nondigestible carbohydrates -- found in whole grains, onions, garlic, leeks, artichokes, asparagus, and chicory root.

Regular intake has been associated with decreases in irritable bowel syndrome and fat storage (and may reduce allergic reactions like skin rashes) -- as well as an increase in an overall feeling of well-being, according to a 2010 issue of the "British Journal of Nutrition."

According to studies done in mice, dietary fats can damage the gut lining, thus allowing the undesirable chemicals released by certain bacteria to leak into the bloodstream and inflame the tissues surrounding it.

What's more, some fats "raise the population of unfriendly bacteria," says Rob Knight, a professor of chemistry and biochemistry at the University of Colorado, Boulder.

Stress may change the makeup of your gut flora. A 2011 "Brain, Behavior, and Immunity" study reported that stressed-out mice (which had been left in a cage with aggressive mice!) experienced a plunge in beneficial bacteria and an increase in inflammatory chemicals in the blood serum.

Stress "alters the functioning of the immune system -- either by suppressing or enhancing its response to foreign invaders," says Ohio State University associate professor of oral biology Michael Bailey, the paper's author.

For the good of your gut -- and health -- figure out why you're anxious, and take measures to eliminate those stressors.