What are the health benefits of probiotics?

by Bianca Nogrady

There's a lot of interest in probiotics and while research has found they can help with a range of conditions, the most effective probiotic treatment is a lot ickier than a dairy drink.

 

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Read enough online and you'd be forgiven for thinking probiotics are some kind of magical bullet that can relieve everything from irritable bowel syndrome and gastro to cancer and high cholesterol.

Probiotics are live microorganisms, such as bacteria or yeast, which when taken in large enough quantities, help improve and maintain the health of your gastrointestinal tract.

Advocates say probiotics boost the populations of good bacteria in your gut, thereby improving not only your gut health, but somehow benefitting all the other aspects of your health that been linked to the gut – including your immune system. This is because the gut encounters foreign substances every day in the food we eat, making it a major line of defence against potentially harmful pathogens.

You only have to head to your nearest chemist, supermarket or health food store to find probiotics, which may come as tablets, powders, drinks and yoghurt. Most of these contain bacteria, such as Lactobacillus and Bifidobacterium, that already live in your gut and help keep you healthy and digesting food; some may also include the yeast Saccharomyces boulardii.

Probiotics have the added advantage that they are relatively safe, as we already have these populations of bacteria in our gut and the most common vehicles for probiotic medication are dairy products found on the shelves of every supermarket.

What does the evidence say?

For some health conditions, such as diarrhoea and particularly antibiotic-associated diarrhoea, there is clear evidence of a benefit from over-the-counter probiotics.

A 2010 Cochrane review of 63 studies examining the use of probiotics in more than 8000 people – most of whom were children – with infectious diarrhoea found those who took probiotics were generally sick for a shorter period and without any adverse effects. The most common probiotics used were L. casei strain, S. boulardii Enterococcus lactic acid bacteria.

Probiotics have also been found to prevent the bouts of diarrhoea that affect up to one in four people taking antibiotics. A recent meta-analysis, which looked at the results of 63 different trials, concluded that taking probiotics could reduce the risk of antibiotic-associated diarrhoea by 42 per cent.

Irritable bowel syndrome, with its range of unpleasant symptoms, including bloating, flatulence and diarrhoea, is another condition often treated over-the-counter with probiotics although the research evidence on this is mixed.

The link between the gut and our immune system has also prompted great interest in the potential benefits of probiotics in treating a range of allergic and auto-immune conditions, such as inflammatory bowel disease and Crohn's. There is growing evidence that gut flora plays a significant part in these diseases, but probiotics are yet to prove conclusively useful in preventing flare-ups. Some studies have found an effect, other studies haven't.

Part of the problem with using over-the-counter probiotics may be that they only consist of a few strains, when we know that the number of potential strains of gut flora run into the millions.

As the evidence suggests, the few strains easily available do have some impact on conditions, such as infectious diarrhoea, but perhaps we are missing the full potential of probiotics.

"You might get a probiotic that contains six to ten strains, so you don't really get the strains that you need, which are the anaerobes," says gastroenterologist Professor Thomas Borody, director of the Centre for Digestive Diseases in Sydney.

Oral probiotics also contain doses of bacteria that are around 3-4 orders of magnitude lower than the estimated 100 trillion individual microorganisms found in the gut.

Borody says another problem with commercial probiotics is that they are too 'tame'.

"Once they've been caught and cultured then they are changed, and they're passaged, which means they're grown over and over and over and the more you passage a bug, the less it is like it used to be," says Borody.

Faecal transplants

What is needed is wild type bacteria that have come from very similar conditions to the human gut. And what better environment to find these in than ... the human gut.

This brings us to another form of probiotic treatment, which you won't find on the shelf of your local pharmacy. It was once known by the descriptive but cringe-inducing name of "yellow soup" but today it is known as faecal transplants, or faecal bacteriotherapy.

"It's probably the only real probiotic, except it's got the 'ick' factor, but it has been done since the fourth century," says Borody.

"So we're using total flora from a donor to put into a recipient, for example, to kill Clostridium difficile, and that has a near 100 per cent success rate."

Faecal transplants are now standard treatment in many places for Clostridium difficile infection, which is the most common cause of antibiotic-associated diarrhoea. A recent study published in the New England Journal of Medicine found this treatment to be significantly more effective, curing 94 per cent of patients, than standard treatment with the antibiotic vancomycin, which cured 27 per cent.

Borody hopes that in the future, faecal transplants might be available in a more palatable form, which he half-jokingly describes as 'crapsules', or a powder that could be added to milk or yoghurt.

In the meantime, in his view 'yellow soup' represents the best that probiotics have to offer.

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