They are advertised with hyperactive parents maniacally monopolising the playground in front of their cringing children and geeks whose dinner-party repartee on the subject turns them into sex gods.
The none-too-subtle message behind the adverts for Britain's £213m market in probiotic or "friendly bacteria" drinks, from Actimel to Yakult, is: drink me and you will become a sleeker, healthier or fitter human being.
But with vague promises that they "may benefit overall well-being" by transplanting six billion microbes into the stomach in two gulps, the proliferation of probiotic products has provoked suspicion that the only thing at which they are highly effective is siphoning cash from consumers' wallets.
Research by Swedish scientists has found that the yoghurt-type drinks are indeed beneficial by apparently boosting the immune system and shortening the effects of minor ailments such as cold or stomach upset.
The researchers gave 94 workers for the packaging giant Tetra Pak a daily probiotic drink and found they were 2.5 times less likely to take time off work for sickness than a group which was given a placebo.
The findings published this week will provide a further boon to the burgeoning market in "neutraceuticals", foods produced with a health-improving additive and sold at a suitable premium, which is now worth nearly £1bn a year in Britain.
From Benecol spread "proven to reduce cholesterol" to Flora ProActiv yoghurt drink containing dairy peptides to "actively help control blood pressure", a trip to the supermarket increasingly involves deciding on a health priority as much as what to eat for dinner.
Experts predict that spending in the sector will double by 2010 as Britons fill their shopping baskets with products ranging from milk containing omega 3 fish oils to SkinCola, an "oxygen-enhanced" mineral water to be launched soon which claims to boost the immune system.
But while nebulous promises to improve well-being have not dissuaded people from buying probiotic drinks - the fastest-growing part of the neutraceuticals industry - there has been little evidence of their vaunted benefits.
Probiotics are harmless bacteria which occur naturally in the large intestine, where they perform a role in stopping unpleasant pathogens such as E.coli or campylobacter entering the bloodstream.
The theory is that by "topping up" these friendly bugs with a probiotic drink, conditions in the gut "micro-flora" are improved, with an knock-on benefit for the immune system.
The Swedish researchers focused on Lactobacillus reuteri, one of the family of bacteria most commonly used in probiotic products, and gave 180 Tetra Pak workers a daily dose containing 100 million of the bugs or a placebo over 80 days.
Of those taking the placebo, 23 fell ill with colds or a stomach upset. Among those given the bacteria, just 10 fell ill.
The effect was most obvious among shift workers, whose irregular hours often lead to a weakened immune system. None of the 26 employees given the L.reuteri fell ill, while nine out of the 27 taking the placebo did. It is thought that the bacteria succeed in stimulating the immune system by attracting white blood cells, which help to combat infection.
Dr Py Tubelius, the author of the study, which was published in the journal Environmental Health, said: "Although the exact mechanism of action cannot be defined from our study, it is likely that such an immune stimulation lies behind the reduced illness in the subject taking L.reuteri.
"This stimulation may also explain why the beneficial effect of L.reuteri in our study was specifically apparent among shift workers. [They] are known to be at risk for having a weaker immuno-defence as compared to those working daytime shifts only."
When added to research suggesting that some probiotic bacteria have anti-carcinogenic properties and may be able to regress or reduce tumours, while others can help protect against diarrhoea, it seems that the arguments in favour of investing in a daily dose of Yakult, Danone's Actimel, Muller's Vitality or any other of their competitors are incontestable.
The sale of the drinks has increased by 50 per cent in the past year, with Danone saying that its product has increased sales by 73 per cent in the past 12 months. The food company said that of the 9.5 million people who bought Actimel during one month last year, only 45 took up its offer of a full refund to anyone who did not feel a "difference" within two weeks.
Crucially, however, Danone declined to define what that difference might be.
Some experts believe that there is a risk that probiotics are being wrongly touted by some as a panacea. Dr Simon Cutting, an international expert in probiotics at the University of London, said: "The health claims made for oral probiotic supplements are generally acceptable. But claims made for yoghurt drinks are often too wishy-washy and general.
"Some marketing is downright misleading and involves meaningless phrases such as 'feelgood bacteria' to generate an unrealistic picture of unobtainable health benefits.
"For the consumer this may all be very frustrating, as they want a more specific claim, for instance that using the probiotic will reduce the symptoms of irritable bowel syndrome."
Experts are also divided on just how much of the useful bacteria contained in probiotics actually reaches the gut. One study estimated that as much as 90 per cent of one probiotic bacteria was killed by stomach acid, meaning that each drink needed to contain at least one billion of the bugs to be useful.
While the most high-profile brands have measures to ensure that the correct "dose" of bacteria is produced, others simply do not.
A survey by Belgian researchers found that just 20 per cent of 55 probiotic products they tested contained all the organisms that were listed on their labels. Nine of the products had no bacteria in them at all.
But there is no sign that such problems are doing anything to dampen the rampant growth in probiotics and other parts of the neutraceutical industry.
Probiotic cheese and fruit juice are already on supermarket shelves, while ice-creams and sorbets are soon to follow.
Which is to mention nothing of the dizzying array of "functional foods" containing health-boosting additives which give new meaning to the word "doctored".
Waitrose earlier this year introduced bread enriched with selenium, the mineral found by some studies potentially to protect against heart conditions.
There are also plans to launch TipTopUp bread, an Australian brand containing omega 3 oils, while Flora, which has seen its fortunes transformed by the arrival of dairy and plant extracts designed to reduce cholesterol and blood pressure, has had to colour-code its ranges to avoid confusing consumers: blue for blood pressure and green for cholesterol.
If combating heart disease by popping a couple of slices into the toaster were not enough, manufacturers are also offering foods that claim to improve beauty. Unsurprisingly, they have been labelled "cosmeceuticals".
Nestlé, the Swiss-based conglomerate, and the cosmetics giant L'Oreal recently launched Inneov, a dietary supplement which claims to improve the look of skin, hair and nails.
A Japanese company has launched a range of foods containing a fatty acid derived from shark skin and whale cartilage which claims to help retain moisture, while the new Emmi yoghurt range contains aloe vera, designed to improve the skin.
Experts point out that such targeted hi-tech nutrition is a positive - and lucrative - response from a food industry battered by criticism that it has fuelled ill-health and obesity with high fat, salt and sugar levels.
But critics claim that some products are based on unproved science or make assertions so bland as to be meaningless.
One marketing expert involved in the launch of a probiotic drink said: "You have to be very careful indeed about what you say this little bottle of sweet liquid will do to improve your life. The blurb has to seduce the consumer but at the same time you can't say drink this and you'll live to 100 because it's just not true."
Whether the lure of science will continue to seduce shoppers into paying extra for a loaf of bread which might come with a promise to cure baldness remains to be seen.
But others point out that the real path to good health lies in a discovery made long before probiotics and omega 3 - the Mediterranean diet of fresh fruit and vegetables, whole grains, olive oil and a small amount of meat and oily fish.
Catherine Collins, chief dietician at St George's Hospital in Tooting, south London, said: "Functional foods containing positive additives are no substitute for a naturally balanced diet. If pursued, there's no need for functional foods."
A bread containing soybean and linseed, both sources of plant oestrogen. Researchers say the phyto-oestrogens can "reduce symptoms of menopause-balance hormones" among women. In Japan, where soya is the staple diet, rates of breast cancer are thought to be the lowest in the world.
Omega-3 fatty acids maintain the heart and circulatory system. DHA is one of the most elusive acids of the Omega-3 family. It is thought to be vital for brain and eye structure in adults. Hens fed on natural Omega-3 DHA then go on to lay these eggs, making the acid palatable for human consumption.
Contains ingredients that may reduce cholesterol levels by up to 14 per cent. These are traces of plant stanol ester often found in corn, wheat and rye. Plant stanols block the body's absorption of cholesterol. Critics say the product will only help reduce cholesterol levels. It will not prevent the build-up of cholesterol altogether.
A Japanese researcher discovered Lactobacillus casei Shirota in 1933. Since then the product has become known across the world. Each 65ml bottle is said to contain around 6.5 billion colonies of bacteria that help the natural balance of the digestive system.
NUTRILAW SELENIUM ENRICHED BREAD
The levels of nutritious elements from soil have steadily fallen with the rise of intensive farming. This bread aims to redress the balance by using wheat specially grown in selenium-enriched soil. According to the maker, four slices a day maintain a healthy immune system. Selenium is also thought to help the heart by acting as an anti-oxidant.
Contains AmealPeptide, a combination of two peptides derived from milk protein. Consumed daily for two to four weeks, tests have shown it to help in controlling high blood pressure.
L. casei Imunitass is a probiotic bacteria.
It reinforces resistance to salmonella and increases protection against dysentery. According to studies, it aids in the prevention of certain kinds of diarrhoea.
The makers say that Omega-6 this contains is an essential fat that comes from vegetables, helping the body to conserve carbohydrate while shedding fat. Omega-6 supports healthy skin and hair and also aids in the regulation of joint inflammation.
Contains Bifidus digestivum that has been selected, the makers say, because of the positive effects it has on the digestive system. It is a live culture that tests have shown can improve the performance of the digestive tract when eaten every day.
FLORA SEMI-SKIMMED MILK WITH PLANT STEROLS
The makers say the plant sterols this contains are clinically proven to lower cholesterol and maintain a healthy heart. They say cholesterol reduction begins within two weeks of drinking the milk regularly.
Additional reporting by Kunal Dutta and Tom PettiforReuse content