Do these friendly bacteria really deliver substantial health benefits?
First there was plain yoghurt, then fruit yoghurts, then yoghurt drinks, and now everyone 's talking about - and apparently consuming - gut-friendly probiotics. Yakult started the trend almost 10 years ago but, since then, big names like Danone, M "uller and Nestl'e have jumped on the milk-train. Now, even supermarkets like Asda and Tesco have their own brands of probiotic drinks.
In fact, probiotic yoghurt, milk and fruit drinks are one of the fastest-growing sectors in food retailing, with UK sales increasing by a staggering 40 per cent each year. According to market researchers AC Nielsen, an estimated 3.5 million Britons now consume probiotic drinks every day in a consumer boom that 's worth about lb150 million a year.
What has propelled the probiotics explosion is something relatively new in mass food-marketing - the concept of quasi-pharmaceutical products known as 'functional foods'.
The human intestines (the gut) are home to around 400 different species of bacteria - some 'good' and some 'bad'. The bad ones, such as Escherichia coli, Salmonella and Clostridium, are often responsible for stomach upsets like diarrhoea. However, these are kept in check by the good bacteria, the principal ones being Lactobacillus acidophilus and bifidobacteria, which are naturally derived from the body 's own lactic acid, and which we obtain from our mothers during pregnancy and breastfeeding. A balance between these two opposing bacterial camps is said to keep the gut flora healthy, thus maintaining the digestive system in good working order.
Probiotic bacteria also have other specific functions: they ferment organic acids into glucose, lower blood cholesterol, synthesise vitamins, break down the enzymes, proteins and fibre in food, and generally boost the immune system. Part of the credit for why we know this must go to Dr Elie Metchnikoff, the Nobel Prize-winning scientist who, in 1907, was the first to see the link between the longevity in a village of Bulgarian peasants and their consumption of live yoghurt.
Yoghurt is simply milk that has been colonised by certain types of Lactobacillus bacteria, some of which mimic the naturally occurring probiotic bacteria in the gut. We 've had nearly a century to test Metchnikoff's theories about yoghurt's health benefits and, last year, nutritional scientists at the prestigious Tufts University in Boston reviewed the evidence. They concluded that there was substantial proof that Lactobacillus-containing yoghurt did have a promising beneficial effect on gastrointestinal health (Am J Clin Nutr, 2004; 80: 245-56).
Other evidence shows that yoghurt bacteria can also inhibit the growth of a wide range of pathogenic bacteria in the gut (J Food Prot, 1977; 40: 820-3), and there 's also indirect evidence that they can generally boost immune function (Eur J Clin Nutr, 2000; 54: 263-7). Small trials suggest that 'live' yoghurt may even have effects beyond the gut, such as in the prevention and cure of vaginal problems due to yeast colonisation (Ann Intern Med, 1992; 116: 3537). Nevertheless, much of the scientific evidence is contradictory.
The evidence for yoghurt-based drinks is much less clear, mainly because probiotic drinks are so new. In fact, little direct research has been done on probiotics at all, let alone on the products we can buy in the shops.
Most of what is known has come from research on probiotic supplements - pills containing lactobacilli or bifidobacteria, usually in powder form. The species/strains most commonly studied and used in nutritional supplements are Lactobacillus acidophilus, L. casei, L. plantarum, L. reuteri, L. salivarius, L. rhamnosus and Bifidobacterium bifidum. These have been shown to be particularly useful as an adjunct to antibiotic therapy. Antibiotics tend to kill off the beneficial gut flora, causing diarrhoea. Probiotic supplements help to recolonise the intestines, thereby preventing most of the gut side-effects of antibiotics (Ann Gastroenterol Hepatol, 1993; 29: 15-8). Likewise, they are equally good at fighting the food-poisoning bugs that cause 'traveller's diarrhoea' (Chemotherapy, 1995; 41: 48-81).
Those are predictable benefits, but what's more interesting are the new findings that show a potential for preventing allergies such as eczema and milk allergy, especially in infants. That 's because the bacteria act as a benign spur to the immature immune system, kick-starting it into action (Br J Nutr, 2002; 88 [Suppl 1]: S19-27).
To add to the difficulties, each brand of drinks used slightly different strains of probiotic bacteria, making it impossible to compare like with like. Occasionally, the claimed benefits of one type of probiotic appear to have been extrapolated from research using an entirely different strain (and, as such, can 't be relied upon) and, in many cases, the available research involved using animals, not people.
Products by M"uller, Tesco and Asda also contained prebiotics (see box above), yet none of the labels included information on the actual amounts of these prebiotics per serving. The effective daily dose of prebiotics for children is believed to be 13 g/day and, for adults, 515 g/day.
So, again, we are left with many uncertainties. We know that probiotics work in principle, but not always in practice. Scientifically, we know a fair amount about yoghurt and probiotic supplements, but too little about most probiotic drinks. But one thing we do know is that many of these drinks do not contain enough bacteria to do us much good (J Dairy Sci, 2000; 83: 894-907). This may be due to either a miserly manufacturer or to the notoriously short shelf-life of probiotics - another reason, we suspect, why manufacturers may be loath to declare the actual quantity of probiotic contents.
The take-home message, then, appears to be that, if you want to be sure of getting a therapeutic dose of probiotic bacteria, it 's probably best to take a supplement made by a reputable company. Or, if you really want a yoghurt drink, why not just make your own? You 'll need milk plus yoghurt and . . . er, that's it.
Distributor: Skane Dairies, Sweden
Price: lb2.49 (6 3 80 mL)
A fruit drink with added probiotics, this offering contains Lactobacillus plantarum 299v, a strain that has been proven to see off more gut pathogens than most other probiotics.
The science behind this product is impressive, showing that it increases beneficial colon fatty acids (Int J Food Microbiol, 1998; 42: 29-38), and may reduce cholesterol (Atherosclerosis, 1998; 137; 437-8).
Uniquely, it also has an inversely related shelf-life factor - the culture gets stronger the longer it 's kept, provided it is stored in an oat-based medium (Nutrition, 1998; 14: 585-94), which is what Sk ane has done here. A further unique point is that it contains no milk or dairy whatever, so it 's okay for vegans and people with allergies.
In addition, Skane appears to be one of the few manufacturers to have declared the probiotic contents on the labelling: ProViva has 20 billion (US) organisms per pot - vastly more than the minimum required for a therapeutic effect. Low in calories, it also contains the least amount of sugar of all the products in our survey.
Distributor: Yakult Honsha
Price: lb2.69 (7 3 65 mL)
Developed by Japanese doctor Minoru Shirota in the 1930s, this is the grandfather of all probiotic drinks, being the first to hit the UK market in 1996. Basically a liquid yoghurt, as it 's fermented, its active ingredient is L. casei Shirota. This lactobacillus strain is believed to survive stomach acids even better than L. acidophilus.
Nevertheless, in common with its rivals, there is no indication of L. casei quantity on the label, though the manufacturer claims that it contains 100 million bacteria/mL, and has proved that at least some live bacteria do reach the intestines (Int J Food Microbiol, 1999; 48: 51-7).
Over the years, copious amounts of research have been done showing the beneficial effects of L. casei in cases of food poisoning, irritable bowel disease, certain cancers and immunity in general - albeit mainly in laboratory animals (Biofactors, 2004; 22: 63-6). Research on humans is much more limited, but Yakult has been shown to be effective in constipation (Can J Gastroenterol, 2003; 17: 655-8), and may help prevent bladder cancer (Urol Int, 2002; 68: 273-80). An unpublished human trial found some protective effect against colon cancer, but a clinical study of the ulcer bug H. pylori showed only a marginal benefit with Yakult (Aliment Pharmacol Ther, 2003; 17: 429-35).
This was the lowest-fat drink in our survey, but it also had the highest carbohydrate content.
Price: lb1.49 (4 3 100 g)
One of the best-known names in the yoghurt business, Danone has ensured that the ingredients in this drink are indeed mainly yoghurt (which can be considered a plus), with added real fruit 'flavourings'.
The downside is that almost 16 per cent of the contents is simply sugar - making this the second highest for sugar in our review.
The active ingredient is L. casei immunitas, Danone's own patented lactobacillus strain, although it's anybody's guess how much of it there is in the product. Scientific research of this strain of L. casei shows it to be more effective than other probiotics at combating disease-causing bacteria (but in mice, so it may not necessarily apply to humans).
In people, unpublished research shows a slight increase in immune function in cases of flu, but not against Candida or tetanus, but a daily dose has been found to benefit a few immune functions (J Physiol Biochem, 2004; 60: 85-91). The bacteria have also been shown to counteract the effects of psychological stress by increasing the number of lymphocytes in the blood (Eur J Nutr, 2004; 43: 381-9).
Orchard Maid Organic Yogurt Drink
Distributor: Anytime Food & Drink
Price: lb1.29 (250 mL)
In the case of this organic yoghurt with added organic fruit juice, the probiotics aren 't in the drink, but - rather bizarrely - encased in the straw you use to suck the liquid. This means you get a dose of bacteria every time you suck.
The bacteria in this product are L. reuteri, a strain widely used in agriculture against gut infections in farm animals, and found to be effective against diarrhoea in children (Pediatr Res, 1996; 39: 184A). One unpublished clinical trial showed that these bacteria can more than halve absenteeism due to gastric/respiratory infections, but the product itself appears to have no supportive evidence.
Among the more expensive in our survey, it wins extra points for being organic and for its long shelf-life (the probiotics last much longer in the straw).
Distributor: M"uller Dairy UK
Price: lb1.69 (6 3 100 g)
Feel-good bacteria is the catchy sales tag for this yoghurt drink, labelled as containing millions of good probiotic bacteria. These are the standard duo of L. acidophilus La-5 and Bifidobacterium species, plus the 'prebiotic' inulin. This is a natural fibre that appears to boost the action of these bacteria, making them more effective, for example, against colon cancer (in rats) (Carcinogenesis, 2002; 23: 1953-60).
The product's sugar content is not declared, but M"uller's added fruit juice is real, the colourings are natural vegetable dyes, and extra vitamins have been thrown in, too.
Probiotic Dairy Drink
Distributor: Asda Stores
Price: lb0.98 (4 3 100 g)
This milky drink contains fruit and the usual pairing of L. acidophilus and bifido-bacteria, with added inulin - possibly intended to rival M "uller's offering. But this drink contains no yoghurt. The 4.2-per-cent fruit content is real (pur 'eed), but the sugar it contains is a fairly high 12 per cent.
There is no research to show what its benefits are, but it scores well on price.
Probiotic Low Fat Health Drink
Distributor: Tesco Stores
Price: lb1.99 (8 3 100 g)
Labelled as 'low fat', this is hardly surprising as this drink basically comprises water and orange fruit pur 'ee, with added probiotics. As with Asda's product, the two plus points are price and the fact that the L. acidophilus La-5 is fortified by inulin. Otherwise, this is unremarkable.
Munch Bunch Drinky +
Price: lb1.95 (6 3 90 g)
This yoghurt-based milk drink is "great for Growing Kids!, says Nestl'e. And it probably is - if the kids usually are given fizzy soft drinks. It contains yoghurt cultures including Lactobacillus fortis (suggesting there are organisms in this product that are not listed on the label). This lactobacillus is Nestl 'e's own gentle probiotic for kids, which can help keep little tummies strong and healthy - a claim for which there appears to be no scientific evidence. Also, it 's low in fat, but high in sugar - which is odd for what is purportedly a healthfood product.