Can bacteria help cure diarrhea as well as cause it? New research suggests the answer is yes. Taking probiotics in capsule, tablet, or powder form can reduce the time required to recover from a bout of diarrhea. Probiotics are supplements offering a dose of "friendly bacteria" – the type that live in your gut and aid digestion every day. They are available to consumers as dietary supplements. They are also added to some foods like yogurt, miso, tempeh, and soy milk.

The interest in probiotics has increased in recent years as more is learned about the role these microorganisms play in the development of the immune system, protection against unfriendly bacteria, and how they aid in the digestion and absorption of nutrients.

A review of 63 studies which included 8,014 people, mainly infants and children, found that probiotics reduced the duration of diarrhea by about 25 hours. Taking probiotics also reduced the risk of diarrhea lasting four or more days by 59%, and resulted in fewer diarrheal stools. No adverse affects were reported.

Because this was a study of many different studies (a meta-analysis), there were some inconsistencies among the studies reviewed, (different strains of probiotics were used, the dosage varied, and so did the length of treatment). This means that while the results are encouraging, more research is needed to learn which probiotics should be used for which groups of people and how cost effective their use could be.

Probiotics are living microorganisms that are similar to the beneficial microorganisms found naturally in the human gastrointestinal tract. Most often probiotics are bacteria that come from one of two groups, Lactobacillus or Bifidobacterium. Within each group of bacteria there are different species and within each species there are different varieties. Some probiotics are yeasts, such as Saccharomyces boulardii.

Probiotics are not new. They date back to ancient times when foods were fermented and milk was cultured. The interest in probiotics has increased in recent years as more is learned about the role these microorganisms play in the development of the immune system, protection against unfriendly bacteria, and how they aid in the digestion and absorption of nutrients.

Everyone has their own mix of bacteria in their body. How these bacteria interact in an individual and how they interact among themselves can affect one’s health. When the balance of friendly to unfriendly bacteria is disturbed, health problems occur. Two factors most often throw off the balance: antibiotics and unfriendly microorganisms.

Antibiotics are not choosy about which bacteria they kill. They kill both the friendly and the unfriendly bacteria in the gut which can cause unpleasant side effects like gas, cramping, and diarrhea. Some people take probiotics when taking antibiotics to offset these side effects.

Unfriendly microorganisms such as disease-causing bacteria, yeast, fungi, and parasites can also upset the balance. Researchers are studying whether probiotics may be helpful in stopping these microorganisms from causing problems and/or suppressing their growth in gastrointestinal conditions such as infectious diarrhea, irritable bowel syndrome, inflammatory bowel diseases, or infection with H. pylori, the bacterium that causes most cases of peptic ulcer disease.

Also under investigation is whether probiotics may be useful for treating tooth decay and periodontal disease, vaginal infections, daycare-acquired stomach and respiratory infections, skin infections, and for boosting the immune system.

The safety of probiotics has not been thoroughly studied, and more information is needed on how safe they are for children, the elderly, and those with compromised immune systems. People considering using a probiotic product should consult their physician.

The study was published in the December issue of the Cochrane Library.