Bowels and their movements are one of Britain's national obsessions. But in recent years this prudish yet sniggering fascination has developed into a health obsession, fuelled by a bevy of yogurt products promising relief from "digestive discomfort".

Probiotic yoghurts and yoghurt drinks, produced by the likes of Yakult, Danone, Müller and Nestlé, contain live "friendly" bacteria that help existing friendly bacteria in the gut fight bad bacteria to improve balance and aid digestion. The UK market for these products, touted as treatments for irritable bowel syndrome and even protection for the immune system, was put at £307m in the year up to July. But they could soon be consigned to the toilet bowl of history with the launch of a range of more sophisticated gut-improving dietary supplements.

The next step in beating bloat is prebiotic food stuffs. While the idea behind probiotic food is to introduce more friendly bacteria into the body, prebiotics work by feeding the good bacteria that is already in the gut. As the stomach is extremely acidic, nutrition scientists say that not enough friendly bacteria in probiotic drinks survive passing through it to improve the health of the large intestine, where most of the gut bacteria live.

Scientist Glenn Gibson, who is researching the impact of prebiotics on gut microbiology, says that a lot of the problems with getting live microbes to sustain in products and during ingestion can be overcome by prebiotic food.

Professor Gibson, head of food biosciences at Reading University, added that because prebiotics are not living organisms - as probiotics are - they can be added to a much wider range of foods.

He said: "They are amenable to incorporation into lots of foods, including those that are heated - heating kills probiotics. You can put prebiotics into baked products, cereals, drinks and yogurts."

Kelloggs launched a prebiotic cereal, Rice Crispies Multigrain, for children in 2004. There are also prebiotic baby milk formulas. But the latest development is prebiotic water. Earlier this month Tyneside company Works with Water launched a range of bottled waters, which contain the prebiotic fibre inulin derived from the root of the chicory plant.

The company's director, Wayne Hayes, has great expectations for the range, which comes in four flavours: plain, cranberry, tutti-frutti and lime and lemon. He said: "We expect to be selling 500,000 bottles in the first year of production and two million in the second year."

But why should we start buying such products given that prebiotics occur naturally in fruits and vegetables such as onions, tomatoes, bananas and leeks? Is it a case of people being too lazy - or lacking the time - to eat well?

Healthy bacteria, including Lactobacillus and Bifidobacterium, account for 10-15% of the bacteria in the gut in adults. But they become depleted through poor diets, such as too much fatty, low fibre, preservative-laden food, plus environmental factors, antibiotics and stress.

Prof Gibson says that only 8% of the UK population eat a healthy balanced diet in terms of consuming the recommended five to eight portions of fruit and vegetables per day. But now that levels of good and bad bacteria can be measured, food scientists can determine how prebiotics can be used to improve gut health, he says.

"The normal prebiotic level in the diet is 2-3 grams per day," says the professor. "You would need an additional five to eight grams per day to get a shift in the positive components of the gut flora.

"Virtually all people do get a gut problem sometime. This is usually acute like gastroenteritis, or can be more chronic like irritable bowel syndrome. So the approach is to use prebiotics - and indeed probiotics - as preventative [treatments]."

Professor Christine Edwards, head of human nutrition at Glasgow University, concurs that most people would find it easier to enhance their diet with prebiotics than eat more healthily. She said: "People find it difficult to have a high-fibre diet but as most prebiotics are very soluble and can be taken without any noticeable impact on the food or drink they are included in, it is a very convenient way to get health benefits."

The advent of prebiotics will not mean the end of probiotics. Prof Edwards says: "The next developments will be synbiotics, which combine prebiotics and probiotics in the same product so that the prebiotic will increase survival of the probiotic in the body."

However, there could well be more far reaching uses for this area of food technology. Prof Gibson says research suggests gut bacteria could in the future be used to tackle obesity and even improve the efficacy of some medicines.

"We may have the potential to use gut bacteria in mediating very prevalent conditions like obesity. It is sure that gut bacteria generate metabolically important signals to their host and we need to get this sorted out. It may also explain why some pharmaceutical drugs work in certain people but not others - ie their gut bacteria handle it differently."