Diarrhea is an extremely common consequence of disturbing the natural balance of your gut's microbiota. In generally healthy individuals, a good diet, rich in fiber, protein and low in fat, will quickly help restore good bacteria. But in older individuals or those with an underlying condition, probiotics may be needed to avoid potentially deadly problems such as overgrowth of bad bacterium like Clostridium difficile. When that bacteria starts to thrive, it can result in an extremely enlarged colon that must be removed and, even then, about 80 percent of patients die.

To avoid such havoc, it's important that you pull the right live bugs off the shelf and that they survive to reach the lower gut, Ms. Cresci says of fragile bacteria that can be lambasted by gastric juices or killed off by even a short-term exposure to ambient heat.

The right combination is essential as well. "A lot of these probiotics have only one bacterium but we have trillions of colony forming units in our gut," she says. There is mounting evidence that one of the best ways to quickly restore the complex gut complement is by using feces from healthy individuals. It's called fecal bacteriotherapy, when feces mixed with a little saline, is given typically via a rectal enema or a nasogastric tube.

The good news is, if you eat right, you likely won't need such extremes.

Ms. Cresci says a good daily diet has:

30 percent or less of calories coming from fat and saturated fats comprising no more than 10 percent of that. The majority should come from monounsaturated fats such as olive and canola oils.

25-30 grams of fiber, not from supplements, but from fiber-rich foods like whole grains and fresh fruits and vegetables, which also provide needed vitamins and minerals.

If tolerable, dairy products to help ensure adequate protein, calcium, and other nutrients.

Protein, through meat or dairy products, or nuts and beans, which also provide fiber and healthy fats.

Source: Medical College of Georgia