Battling my way around the supermarket aisles, bamboozled by the array of new products on the shelves, I am suddenly aware of an invasive life form taking hold of the chiller cabinet. Having turned yoghurts into drinks, the marketing men have decided to woo us with science, by plastering the word "probiotic" on the pots.
The blurb tells us that they are good for us; that they aid digestive health; and that they give our guts that most elusive elixir of 21st century life - balance.
But if you don’t have time to peruse the fine print on those little bottles of Yakult, Danone Actimel et al, you may have walked on by to the check-out simply because you don’t know what a probiotic is.
Even if you do, you may well be wondering how much scientific evidence exists to back the manufacturers’ claims that they are good for your health.
Probiotics - which means "for life" - are so-called "friendly bacteria" which are believed to be beneficial in maintaining a healthy digestive system.
The human gut is home to around 400 different species of bugs, some good, and some bad. The Lactobacillus and Bifidobacterium lurking there are probiotic species of bugs which aid digestion by breaking down tough fibres, enzymes and other proteins in our food. Probiotics also produce important nutrients such as vitamin K, and ferment organic acids which are absorbed into the bloodstream for energy.
However, these good guys have to share their habitat with bad bugs such as E.Coli, Salmonella and Clostridium - bugs which are responsible for most bouts of diarrhoea, and which can prove fatal.
The balance between the good and bad bacteria is key to maintaining good digestive health, and when all is well our digestive systems are a relatively stable "microflora".
So if probiotics are already part of the body’s natural make-up, why pay to throw even more of them down our throats? The answer to that lies in the daily assaults our digestive system receives from what we consume, and the way we live.
Stress, illness and prescription medicines can all play havoc with the bacterial balance. Antibiotics pose particular problems, because as well as killing off the bad bacteria for which they were prescribed, they kill off the good guys too.
It is in a bid to restore balance - or guard against imbalance - that most people turn to probiotic products.
Probiotics certainly have an army of fans, with the worldwide markets for products such as Yakult, Danone, Actimel and the like estimated to stand at 3.3 billion a year.
Over the past century or so probiotics have been credited with alleviating symptoms in a range of illnesses, from constipation and irritable bowel syndrome, to more serious gut complaints such as ulcerative colitis and Crohn’s disease. They have also been applied in the treatment of vaginal, urinary tract, dental, ear and wound infections. In addition, they have been shown to reduce the length of illness in some of the 100,000 cases of food poisoning seen in the UK annually due to pathogen - or disease causing - bacteria.
But how big is the body of scientific evidence that probiotics actually work?
Probiotics have had almost a century to prove themselves. The concept first emerged in 1907, when Elie Metchnikoff, the Nobel Prize winning scientist, attributed the longevity of a Bulgarian peasant village to its inhabitants’ consumption of live yoghurt. Metchnikoff’s work influenced a Japanese doctor, Minoru Shirota, who in 1935 developed a fermented milk drink containing the unique probiotic, Lactobacillus casei shirota. Shirota claimed this bacteria was beneficial, and named it Yakult - the Esperanto word for yoghurt. The probiotic drink was born.
Since then a number of well designed clinical trials have shown beneficial effects of probiotics in the treatment of travellers’ diarrhoea, acute diarrhoea in children and antibiotic associated diarrhoea. Other trials have also shown that lactobacilli taken as live yoghurt or vaginal tablets can successfully treat vaginal bacterial and Candida infections. One Canadian research team has had some success in using intravaginal probiotics to treat recurrent urinary tract infections. Trials also suggest that such bacteria can have a beneficial effect on the immune system.
One Finnish study found that giving a daily dose of the probiotic Lactobacillus rhamnosus bacteria to pregnant women and their babies during the first six months of life reduced the incidence of eczema, when compared with a control group which did not receive the bacteria.
The Bifidobacteria which are present in breast milk, are also known to rapidly colonise the guts of breast-fed babies, who suffer fewer gastrointestinal infections as a result. Scientists are now wondering if probiotics could play a part in the immunisation of babies, and if it would be beneficial to add probiotic substances to infant milk formulas.
A similar approach is already being used by the United States Agricultural Research Service to reduce levels of disease-causing bacteria such as Salmonella and Campylobacter in poultry. Newly hatched birds are fed probiotic bacteria to prevent their guts being colonised with bacteria, which have the potential to cause food-borne illness in humans.
Professor Tom MacDonald, a gut immunologist at Southampton University, is currently looking at various aspects of immune function in healthy individuals taking the probiotic drink Actimel.
He says that the scientific community is very interested in the use of probiotics in treating inflammatory bowel diseases such as ulcerative colitis and crohn’s, but says there is a paucity of good clinical trials in this area.
Professor George MacFarlane, a bacteriologist at the Medical Research Council Microbiology and Gut Biology Unit at Ninewells Hospital in Dundee, may have found a way to make the "probiotic hit" more effective. Researchers recently completed a pilot study in ulcerative colitis of a "synbiotic" - a prebiotic given in combination with a probiotic - which he says gives the probiotic a better opportunity to establish itself in the bowel.
"We found that there were differences in the populations of Bifidobacteria in the gut lining of healthy people compared with ulcerative colitis patients. We then selected a Bifidobacterium from a healthy mucosa [gut lining] and looked to see whether it had probiotic qualities and whether it grew well on the probiotic," he says. Colitis patients were given the synbiotic for a month in a double-blind placebo-controlled trial. The results are yet to be published, but Prof MacFarlane says it found marked improvements in clinical appearance and reduced inflammation.
Considering the apparent benefits of probiotics, they were slow to arrive in the UK. Yakult launched in Japan in 1955, but it only started manufacturing in Europe in 1994 and did not reach the UK until 1996. Danone launched its probiotic drink Actimel in Belgium in 1994, and it now sells in 26 countries, with an estimated 6 million bottles being consumed daily. Danone claims its patented probiotic, Lactobacillus.casei.immunitass, "helps support your body’s natural defences". Muller introduced their probiotic, Provitality, range in 2000. Probiotic products seem to be proliferating faster than a bacterial culture.
But if research has been lacking in some areas, that seems about to change. Although technically rivals, Danone and Yakult recently announced that they are to collaborate more closely on the development of probiotic products. The EU recently invested more than 15 million on research in this area, and a forthcoming directive on food labelling may allow probiotic products to carry wider claims about their health benefits.
But what does all this mean when you are doing your supermarket shop? Should you go probiotic? And if so, how much should you consume, and how often? Scientists point out that the intestinal microflora is carefully balanced, and therefore it is difficult for invading bacteria to gain a foothold - and that goes for probiotic strains too. For that reason, it is generally recommended that probiotics are taken on a daily basis.
Professor Colette Shortt, director of science at Yakult, says: "We carried out a study of healthy individuals in the Netherlands, and that showed that there were increased levels of the actual probiotic strain. However, after seven days or so the levels of bacteria fall. So there is only a transient colonisation. The probiotics have to be ingested regularly to maintain levels." Results which are sure to maintain sales.
If probiotics attract you, but those pale liquids don’t, check out health food shops for capsule forms - or try prebiotic tablets which aim to selectively stimulate the growth of good bacteria.
The Food Standards Agency in England is due to publish the results of two surveys shortly, one on the persistence of probiotics in the lower bowel, the other on the labelling of probiotic foodstuffs and supplements. The results should pave the way for tighter regulation of health claims on all foodstuffs - including probiotics - and so make it easier for consumers to make informed choices.
Meanwhile, the gut feeling among experts seems to be that consumption of probiotics may have health benefits for us all. Professor MacDonald says: "They certainly don’t do any harm. And compared with other things we put in our mouths, probiotics are not so bad."
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