More than 400 types of bacteria live in the human digestive system. Many of these bacteria types are good bacteria — they help the digestive system to do its job. Good bacteria, like acidophilus and bifidobacterium, may also prevent disease by making an unfavorable environment for less desirable bacteria.

Good bacteria can do several things to promote health. It helps to break down plant starches and other foods that the human body has difficulty digesting. This allows the body to convert more food into energy. Good bacteria also help the body to turn extra calories into fat. This may lead to the idea that a person's inclination towards obesity may be partially due to the type of bacteria in his or her digestive tract.

The human body does not make vitamin K by itself. Bacteria create this, and other essential vitamins, as by-products of the food and other digestive materials they ingest. They also help our bodies to break down drugs and carcinogens, which can cause cancer. This is not the only way that bacteria help to prevent cancer, however. They also help the walls of the digestive tract to renew themselves. This regular renewal gets rid of damaged cells that could lead to cancer.

Although good bacteria find their way into the human digestive system naturally, they don't always remain there. Antibiotics, used for treating illnesses, wipe almost all of the bacteria out of the body, not just the bad stuff. A stomach virus can also drastically reduce the amount of bacterium in the digestive system. The body will build up its supply of good bacteria naturally, but it is also possible to introduce the bacteria through probiotics.

Probiotics are available as nutritional supplements. They are also in yogurt, infants' formula, and some other foods. They are a substance that contains live bacteria, most commonly lactobacillus. When the foods are ingested, the bacteria are deposited into the digestive tract. Probiotics are most beneficial when they are found in yogurt and other products that are kept cold. Heat, too much or too little moisture, or oxygen may destroy active bacteria cultures, making the product less effective.

Good bacteria are essential for good health. They can help to prevent cancer and stomach bugs, and increase digestive times. There have even been studies that prove that regularly consuming probiotics can reduce a person's risk for developing the common cold and respiratory illnesses. Research is being aimed at the possibility of developing probiotics to target specific diseases in the future, perhaps even a cure for the common cold.