We know they're good for digestive health, but could probiotics have other benefits? Christine Piper seeks the latest expert advice.
They've been touted as a miracle of modern science, but you may be surprised to learn that probiotics, or so-called 'good bacteria', have been used by humans for thousands of years.
The ancient Egyptians and Sudanese used lactic acid bacteria to preserve meat and dairy foods. In 1908 – long before the term 'probiotic' was coined – Nobel prize-winning, Russian micro-biologist Ilya Ilyich Mechnikov studied a group of Bulgarian mountain peasants and concluded that the lactic acid bacteria in the sour milk and yoghurt of their diet helped their unusual longevity.
But what exactly are probiotics?
Literally meaning 'for life', probiotics are bacteria that help balance the bacterial population of the gut. Probiotics naturally occur in fermented foods such as unpasteurised yoghurt, kefir (a beverage made from fermented milk that's popular in Eastern Europe), unpasteurised sauerkraut and miso paste. The strains found at supermarkets today are commonly the Lactobacilli and the Bifidobacteria found in dairy products and probiotic formulas.
A healthy gut contains a whopping 1.5kg of microorganisms (that's 100 trillion), including more than 400 different species of bacteria – harmful bacteria that can cause disease, and beneficial bacteria that aid digestion and form a protective barrier around the intestine. Kate Di Prima, dietitian and author of More Peas Please, explains: "The integrity of the gut relies on the healthy numbers of these bacteria in your gut. If you've got a good gut lining, you'll have absorption of vitamins, minerals, nutrients, and good evacuation of waste."
Meet the colony
We all have a unique set of microorganisms in our gut, called a 'flora'. This is formed during the first few months of our life, when our bodies absorb the numerous strains of bacteria that we're exposed to in the air, in our food and drink (including breast milk), and in our environment, and accept them as our own.
Reproducing rapidly, these bacteria set in place an inner ecosystem that stays with us for life. "Your gut bacteria are like a fingerprint – so specific, that even if you eradicate them, they will always grow back to your profile, because that was the profile you were tolerant of as a baby," explains Eric Claassen, professor of immunology at the Erasmus Medical Centre in the Netherlands.
Upsetting the balance
For the most part, good and bad bacteria live together harmoniously in a healthy gut as part of a diverse community. But a number of factors can upset that delicate balance: stress, drugs, too much alcohol and an unhealthy diet.
"Bad bacteria can live on simple sugars, but good bacteria need complex sugars. So with the introduction of simple, refined sugars in our diet, we give the bad bacteria an advantage," Professor Claassen explains.
Antibiotics are another common cause of imbalance in the gut, as they eliminate both good and bad bugs – in some cases resulting in the bad ones growing back faster than the good. When the bad bugs gain control of the gut, they can produce numerous toxic compounds, such as hydrogen sulphide, which can lead to bloating, diarrhoea and cramps. This is where probiotics can come in handy, as they can reduce the number of harmful bacteria in your gut by attaching to the wall of the intestine and creating an acidic environment, making it less comfortable for them to populate. Probiotics also expedite the breakdown of organic waste in the gut and create useful enzymes, such as lactase, which helps the body break down lactose.
"As far as evidence goes, antibiotic-caused diarrhoea and infectious diarrhoea have the strongest evidence [that probiotics have a beneficial effect]," says Dr Tim Crowe, dietitian and senior lecturer in the School of Exercise and Nutrition Sciences at Deakin University, Australia.
A study published in 2007 found that elderly hospital patients were 22 per cent less likely to experience a bout of diarrhoea following antibiotic treatment if they were given a probiotic drink. But it is not just a case of taking one dose and feeling well again. It's about regularly ingesting probiotics to reap long-term benefits, as the ecology of your gut changes every three to four days.
Immunity, UTIs and IBS
Much of the buzz surrounding probiotics stems from their potential to power up our immune systems. As one of the body's earliest lines of defence, the gastro-intestinal tract (where an estimated 70 per cent of the immune system is located) plays a key role in the immune system by processing the food we eat, and helping prevent bad bacteria from infecting the bloodstream and other organs.
"[Probiotics] can directly affect the immune system," Professor Claassen explains. "They produce cytokines, which are messenger molecules that help the cells of your immune system combat pathogens. By stimulating the immune system, all your defence mechanisms go into overdrive."
As well as enhancing our immune systems, Dr Crowe says probiotics may help a multitude of other conditions – from respiratory and urinary tract infections to irritable bowels – but the jury's still out on some of these claims.
"There's good evidence at this stage that for inflammatory bowel disease and ulcerative colitis, probiotics may be of benefit," he says. "Then there are other conditions where the evidence is less [conclusive]: irritable bowel syndrome, certain allergic disorders [and] urinary tract infections."
There's been some suggestion that probiotics may help with weight management. In a study published in May 2009, Finnish researchers found that pregnant women who were given daily doses of two probiotics during pregnancy and for up to six months after birth had less central body fat a year after giving birth than women who did not receive probiotics. However, Dr Crowe says it's too early to accept such evidence as gospel.
"This field of probiotics and weight loss is in its complete infancy…," he says. "There's not a lot of evidence that it will give you a strong advantage in losing weight."
Allergies and asthma
For allergy, asthma and eczema sufferers, research findings indicate probiotics are not largely effective in the treatment of allergies. However, when it comes to preventing allergic development in infants, the results are more promising.
Associate Professor Mimi Tang, a paediatric allergist, immunopathologist and immunologist at the Murdoch Children's Research Institute in the Royal Children's Hospital in Australia, says: "There have been about six studies looking at the effect of probiotics on the prevention of eczema. The ones that showed a beneficial effect used the probiotic when the mother was pregnant, and they were also given to the baby for six months."
Another growing area of interest is the use of probiotics in cancer management.
"There's good research to show that people who have bladder cancer and who take a probiotic are less likely to have the cancer come back again," Dr Crowe says. This research includes a 2007 study which found that bladder cancer patients who had chemotherapy combined with daily doses of probiotic-rich Yakult (drink) following surgery had a greatly reduced recurrence rate than patients who had chemotherapy alone.
Probiotics may soon be accepted as a method to reduce the risk of bowel cancer, too. "Some initial studies in a laboratory indicate the benefit, and there's a large-scale study going on in Europe [now]," Dr Crowe says.
So, are probiotics worth it?
If the facts surrounding probiotics still seem murky to you, you're not alone – even professionals are in the dark about many aspects of this complex field. Much of the confusion stems from the fact that there are huge gaps in the research.
Professor of gastroenterology at Monash University and head of medicine at Eastern Health in Victoria, Australia, Professor Gibson says: "The original concept of probiotics was that they were going to help in keeping people well and prevent conditions. It's very hard to prove [that] without a huge amount of money, a huge study. That sort of money will only come from the companies. If they do that and show that it doesn't work, they've lost their market."
Although on some counts probiotics are yet to live up to the hype, most of the experts agree they're generally safe to use. (Only one study has found probiotics to be extremely harmful – a 2008 study in which twice as many patients with acute pancreatitis died after being given probiotics than those given a placebo).
Perhaps probiotics' biggest benefit, then, is their ability to give power to the people: taking control of one's health as a consumer is hugely appealing, and could be the reason why the industry is now worth almost $21 billion worldwide.
"It does fascinate people, and it has helped us a lot in understanding biology, but we still don't know whether probiotics improve our general health if we take them all the time," Professor Gibson says. "[But] there are lots of good studies being done. And the more data we get, the more their place is going to be established, at least in conservative medicine."
What about prebiotics?
Prebiotics is the name given to the non-digestible carbohydrates we eat that travel through our digestive systems, ready for good bugs to feed on.
Dietitian Kate Di Prima explains: "Bacteria in your gut need what we call prebiotics, found in fruits and vegetables, and in cereal and bread, to live and ferment, to keep alive."
The combined use of prebiotics and probiotics is known as 'synbiotics' (the assumption being they work more efficiently together) – a promising area of microbial research.
Good sources of prebiotics include onions, leeks, soybeans, garlic, bananas, artichokes, oats, bread, cereal, and prebiotic yoghurt/milk.
Tips on buying probiotics
"There have been a few studies which have shown that many probiotics on the shelves are not in very good shape," Professor Gibson says. "The bacteria's supposed to be alive, but they're not." Similar studies have yet to be conducted in Australasia, but to ensure you get the most bang for your buck, keep the following in mind:
- Probiotics need to be alive, so check the use-by date – the fresher, the better. The shelf life of most probiotics products is three to six weeks, and up to 12 months for capsules. Avoid products which haven't been stored as recommended (such as not being refrigerated).
- When it comes to bugs, quantity counts. Products labelled 'probiotic' must contain at least one million bacteria per gram, but 10 million is advised to reap the benefits.
- Look for 'live and active cultures', and avoid products which say 'made with active cultures' – they may have been heat-treated, which kills the bacteria.
- Choose products that specify the genus (eg. Lactobacillus), species (eg. rhamnosus) and strain (eg. GG).
- Look for evidence the product has been 'clinically proven', or tested in clinical trials.