What are probiotics, who should take them, and where do you find them?

Interest in the reported health benefits of probiotics has grown in the past decade, and researchers continue to investigate how the supplements can treat or prevent specific illnesses. Probiotics are well-recognized for their ability to calm bowel inflammation in certain diseases, particularly viral diarrhea, and they're also helpful in reducing the incidence of severe diarrhea in patients being treated for cancer.

On the research front they are being evaluated for use in a number of skin disorders, and animal studies suggest probiotics may play a role in the prevention of cancer. But the supplements are not universally beneficial, and they're not recommended for all patients. Let's take a closer look at these tiny organisms and what they do.

What are probiotics?

Probiotics are defined as "live microbial food ingredients that are beneficial to health." Lactobacilli and bifidobacteria are well known examples. Why would anyone want to eat a live microscopic organism? Trillions of these tiny creatures have already set up camp in our gastrointestinal (GI) tracts. They compose our GI flora, and they often perform useful functions like modulating our immune system, producing vitamins, and occupying space to block the growth of harmful bacteria.

Prebiotics are non-digestible food ingredients, typically carbohydrates or soluble fiber, which stimulate growth of these health-promoting bacteria in the colon. When factors like stress, diet, and antibiotics alter the composition of bacteria in our bowels, prebiotics and probiotics restore balance by replenishing the good bacteria in our bowels.

The notion that "good bacteria" compete with "bad bacteria" for occupancy in our bowels is generally well accepted. But other functions of probiotics have recently come to light. These health-promoting bacteria are thought to help in a number of ways, including strengthening protective lining of our bowels; producing lactic acid which lowers intestinal pH and favors the growth of beneficial organisms; and enhancing the immune response by stimulating the production of chemicals that destroy or inhibit infective bacteria.

Who should take probiotics?

Probiotics are beneficial in a number of disorders, including recurrent vaginal yeast infections, irritable bowel syndrome (IBS), lactose intolerance, diarrhea caused by antibiotics, viral diarrhea, and diarrhea caused by the bacterium Clostridium difficile. But not all patients with diarrhea benefit from the supplements, and they are not helpful in most cases of bacterial infections of the bowel, particularly those that cause bloody diarrhea.

Do probiotics have a role in preventing or fighting cancer?

Research in animals suggests probiotic supplements have a protective effect on the GI tract during and after exposure to a carcinogen (cancer-causing agent), leading to speculation that probiotics could help prevent the development of colon cancer. It is thought lactic acid- producing bacteria can bind to and degrade carcinogens, produce compounds that inhibit the growth of tumors, and enhance our immune system's ability to fight cancer cells. Whether these effects will translate in human studies remains to be seen.