She equates the good bacterium in your gastrointestinal tract to another living being inside that helps keeps you healthy.

"If you do good by your bacteria, they will do good by you," Ms. Cresci says.

There is even mounting evidence that a healthy gut microbiota helps maintain a healthy weight. Studies have shown, for example, that when bacteria from a genetically fat mouse are placed in a lean germ-free mouse, it gains weight without changing its food intake.

Unfortunately poor diets are hurting the bacteria in many of us and the overuse of antibiotics is taking its toll as well, particularly the common, broad-spectrum antibiotics that wipe out anything in their path, good and bad bacteria included.

Cresci cites inadequate fiber and excess unhealthful fats as contributing to the problem, and states that a good daily diet has adequate high-quality protein, fiber, healthy fats and fresh fruits and vegetables.