Probiotics are cultures of beneficial bacteria that are normally present in a healthy digestive tract, for instance, the bacteria which turn milk into yogurt. Medical research on the applications of probiotics is a growing field. While there is a lot we do not know, here is the evidence so far:

>>Lower frequency and duration of diarrhoea

If you or your baby have got the runs, then a probiotic can help shorten the number of days that you spend sitting in the toilet.

Associate Professor Quak Seng Hock, senior consultant paediatrician at The Children's Medical Institute in the National University Hospital (NUH), told Mind Your Body that probiotics are used to shorten the duration of diarrhoea for children with acute gastroenteritis and rotavirus infections.

While probiotics are not as useful in constipation, they are very helpful in controlling antibiotic-induced diarrhoea.

As antibiotics ward off bacterial infections, they also deplete the gut of good bacteria. When gut flora is disturbed this way, intestinal movement is affected and the lining may become hypersensitive. The result could be irritable bowel syndrome and chronic inflammatory bowel conditions.

Taking probiotics can help rebalance the gut environment. Even adults with gastric problems caused by long-term antibiotics can find some relief with probiotics, said Dr Teoh Tiong Ann, a consultant colorectal surgeon at Mount Elizabeth Hospital.

'I tell my patients to either take yogurt or fermented milk drinks like Vitagen,' he said.

>>Stimulates immunity

Dr Law Ngai Moh, consultant gastroenterologist at Raffles Hospital, says gut flora play an important role in promoting intestinal health and gut immunity.

'These bacteria produce antimicrobial substances and compete with the bad bacteria to adhere to the gut lining thus preventing the latter from causing infection and inflammation of the gut,' he said.

In addition, gut flora help the body to absorb important nutrients and stimulate gut immunity against harmful bacteria.

Studies done in Japan have shown that a probiotic strain called lactobacillus casei Shirota (the strain present in Yakult drinks) injected into mice enhanced the immune response significantly.

Another study in Japan showed that when patients with superficial bladder cancer were given a daily probiotic, they had lower rates of recurring tumours compared to those not given a probiotic preparation.

The mechanism by which probiotics enhance immunity is not very clearly understood, but research is ongoing in this area.

Scientists say that in the future, lactic acid bacteria may be used to immunise against various infections affecting the intestines, vagina and respiratory tract.

>>Allergy

Prof Quak of NUH also noted that giving probiotics early in life may decrease the incidence of allergies.

Breast milk is an excellent source of probiotics and prebiotics and is therefore the best food for babies. Studies now show that infants given formula containing probiotics have roughly half as many bouts of fever and diarrhoea as babies given regular formula.

One important study showed that pregnant women given a particular strain of a probiotic for four weeks before they had their babies and then to newborn children at high risk of allergy, reduced their risk of developing allergies quite significantly. This could be an important new area of use for lactic acid bacteria and research is ongoing.

>>Women's health

Research shows that certain strains of lactobacillus can colonise the vagina when used in a suppository. They reduce the risk of recurring urinary tract infections, yeast infections and bacterial vaginosis.

In fact, one study found that probiotics were just as good as long-term antibiotics in staving off urinary tract infections. Plus, lactobacillus therapy taken once a week did not have any of the gastrointestinal side effects caused by the antibiotics.

>>Preventing surgical infections

Before antibiotics and antiseptics were invented, it is said that fermented milk was used to heal wounds and fight infection.

Some intriguing new studies are showing that there might be some truth in this old wives' tale.

In one study, patients fed probiotics before a liver transplant had less risk of post-operative infections and sepsis. In another such study, patients undergoing major abdominal surgery who were given probiotics had fewer infections and shorter hospital stays.

However, further studies are needed before giving probiotics to patients whose immunity may be compromised as they may be at risk for developing bacterial infections.

>>A word of caution

Pregnant women and nursing mothers should use probiotic nutritional supplements only if recommended by their doctors.

The use of probiotics for the treatment of any health problem must be medically supervised.

Most people take well to probiotics but the most common adverse reactions include flatulence, wind and constipation.

People with low immunity should not take probiotics as they risk developing serious bacterial infections or sepsis.

>>Commonly available strains

Lactobacillus acidophilus: Relief from indigestion and diarrhoea, maintains gut health after antibiotic use.

Lactobacillus rhamnosus: Used to treat acute diarrhoea in children, in combination with oral rehydration.

Lactobacillus reuteri: Found in breast milk and suppresses growth of harmful bacteria.

Lactobacillus casei: Improves digestion and reduces milk intolerance and constipation.

Bifidobacterium lactis: Stimulates the immune response, may help reduce incidence of infections.

Bifidobacterium infantis: May help relieve many of the symptoms associated with irritable bowel syndrome (IBS) in women, including diarrhoea and constipation.

Bifidobacterium longum: Keeps the digestive system running smoothly, blocks the growth of harmful bacteria, and boosts the immune system.

>>Dosage

- The recommended doses range from 1 billion to 10 billion colony-forming units (CFU) if taking capsules, or a drink a day if taking fermented drinks.
- A daily supplement for one to two weeks may improve conditions such as infectious or antibiotic-related diarrhoea.
- The micro-organisms in probiotic supplements may die on exposure to heat, moisture or air. Some require refrigeration.

- SHEFALI SRINIVAS

Probiotics and prebiotics - the connection

Though the concept of prebiotics in products may seem new, they have actually always gone hand in hand with probiotic bacteria.

In essence, a prebiotic is a substance that humans cannot digest, but which probiotics feed on. So the benefits of prebiotics are similar to those of probiotics.

According to food science experts, because prebiotics are not 'live', they are far easier to incorporate into consumables such as infant formula, baked goods and other eatables that need to go through processing with heat.

To be effective, prebiotics must escape digestion in the upper gastrointestinal tract and be available for use by some of the good bacteria in the colon.

Prebiotics are a kind of carbohydrate called oligosaccharides.

Research on prebiotics so far has shown that these substances play a role in stimulating immunity, decreasing the risk of colon cancer and promoting calcium absorption in the colon, apart from enhancing probiotic activities.

There are many different kinds of prebiotics, each giving a hand with different probiotic activity.

One of the most used prebiotics is a compound called Fructo-Oligosaccharides (FOS) which helps stimulate the growth of the Bifidobacterium species in the large intestine. Many new products are being marketed with a probiotic and FOS added, both in Japan and the US.

Japan has the widest range of prebiotics on the market with various specified health uses, and in combination with probiotic products such as fermented milks and live yogurts.

Other important prebiotics include inulins, derived from roots of chicory and Jerusalem artichokes, and soy oligosaccharides from soya beans. They also stimulate the growth of the Bifidobacterium species in the large intestine.

• Eventually, there will be more synbiotic products on the market, combining a prebiotic and probiotic to improve the survival and implantation of live bacteria in the digestive tract.