THE thought of eating live animals certainly fills most of us with disgust. And yet, we do it all the time. These are "animals" too small to be seen by the naked eye. They are microorganisms, mainly bacteria. And their ingestion does us a lot of good. In India, yoghurt and lassi are two popular products that are full of bacteria. Other countries have their own specialities - all products of fermentation, that are replete with microbes.

Colette Shortt, science manager for Yakult, a UK-based company, discusses current thinking on the usefulness of food of this type, termed "probiotic" food, in an interesting report in a recent issue of Chemistry and Industry (No 12, Vol 34). Probiotic bacteria are defined by two characteristics: they can thrive in the harsh environment of the human intestines and they stimulate the growth and activity of other useful and the "health-friendly" bacteria. If you thought that these were harmful, rest assured - they are not. Most known probiotic bacteria belong to the groups Lactobacillus and Bifidobacteria.

Most of these bacteria reside in our intestines. Acquired soon after birth, their total weight can often go up to a kg. The total number of species can be counted in the hundreds while their density varies from about 10,000 per gram in the stomach to 10 billion per gram in the large intestine. Their population can be as high as a hundred million cells - about ten times the total number of our own cells in the body.

Traditional practices of medicine have long recognised the importance of useful miocroorganism in the diet, though almost certainly without recognising their bacterial origin. These have also known that there are other, harmful bacteria, and the universal practice of avoiding spoilt food is a tacit recognition of their existence. More recently, several scientists went on record advocating yoghurt as a means of prolonging life. These scientists went so far as to say that the long life expectancy of Bulgarian peasants could be attributed to the huge amounts of yoghurt (containing Lactobacillus) in their daily diet. What exactly happens if we eat pro-biotic bacteria? The first thing to know is that unlike medicines taken for a quick cure, these bacteria need to form a regular component of our diet if they are to do any good at all. This is because their colonisation in the lower intestine depends on the frequency of their consumption. One experiment revealed that their density dropped to a near-zero level within some eight days if they are not eaten regularly. Both Lactobacteria and Bifidobacteria are effective anti-microbial agents against the harmful microbes present in the intestine such as Salmonella, Listeria and Escherichia. Further, there have been claims that probiotic bacteria inhibit the growth of stomach ulcers-causing Helicobacter and boost our immune response.

How about specific studies? A major medical benefit is in the control of diarrhoea caused by rotavirus, which kills about half a million infants a year all over the world. Using Lactobacillus preparations in food or drink is remark-ably helpful in tackling diarrhoea. It has been claimed that probiotic bacteria, combined with measures to avoid allergy-inducing germs, are helpful in dealing with food allergies and also allergic dermatitis. To take things a little further, a disputed study even claims that the level of blood cholesterol - specifically, the low-density or "bad" lipoprotein component of cholesterol - is significantly lowered by eating probiotic bacteria.

Reports have also talked of microbial enzymes that often cause mutagenic products to build up and how probiotic food might play an important anti-cancer role by obstructing the activity of these enzymes. A recent Japanese study has shown that when bladder cancer patients were maintained on a diet that included Lactobacillus casei, only 21 per cent of the patients had a recurrence of the disease over a period of one year, as against a recurrence frequency of nearly 45 per cent in patients who received a placebo instead.

Contemporary research in the area of probiotics has been fuelled mainly by the recognition of the commercial benefits to be had in promoting their use. In Europe alone, the market for probiotic yoghurt is currently worth a staggering Rs 2,500 crores. Given the richness and variety of diets in India and the common use of fermented foods even among urban dwellers, this calls out for a serious program of documentation, followed by research into the probacterial components of traditional foods and their possible use for health, medicine and therapy.