Probiotics – or 'good' bacteria - are among a growing number of 'functional' foods that it is claimed may have health benefits over and above their nutritional value. Prebiotics provide the 'food' on which probiotics feed. But can either of them really make us healthier and, if so, how?
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Our digestion and probiotics
Our guts are home to around 100 trillion bacteria, amounting to 90-95 per cent of all the cells in our bodies; scientists refer to them as gut microflora. In fact, according to Professor Jeremy Nicholson of London’s Imperial College, "The average person has around one and a half kilograms of gut microflora – that’s as big as a major organ."
Throughout our lives these microflora perform vital roles, affecting how well we absorb nutrients, how much energy we get from food and how efficiently we break down food and drugs. "One reason humans are able to metabolise drugs is because we have evolved ways to deal with bacterial toxins," says Professor Nicholson.
Above all our gut microflora are critical to the strength of our immune systems, as Professor Glen Gibson, of the School of Food Biosciences at Reading University, observes, "Some 60-70% of our immune system is in our guts."
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Treat irritable bowel syndrome
If the balance of gut microflora is disturbed, for example by a stomach upset or a course of antibiotics, digestive upsets may occur and we may even develop permanent digestive problems, such as irritable bowel syndrome (IBS). This is why many doctors now advise routinely taking probiotics if you are taking antibiotics.
Among the many diseases that are now thought to be caused, or exacerbated, by disrupted gut microflora, are inflammatory bowel diseases, such as ulcerative colitis and Crohn’s disease, obesity, mental health problems such as schizophrenia and autism and the infection C difficile.
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Eating live yoghurt
Probiotics, usually described as 'friendly bacteria', are said to help restore the balance of gut microflora to keep us healthy. They are found in live or bio-yoghurts and 'functional' yoghurt, milk and fruit drinks and they are also available as tablets or capsules. Professor Gibson points out that humans have been consuming probiotics for thousands of years in soured milk products like yogurt and buttermilk. In fact the longevity of certain communities has been attributed to their consumption of live yogurt.
Most of the favourable research on probiotics relates to their ability to ease gastro-intestinal complaints. "Research has shown that taking probiotics can help shorten a bout of infection such as traveller’s diarrhoea, colds and flu," says Professor Gibson.
But there are also intriguing hints that they may be able to protect against more serious problems. It’s fairly well-established, for example, that bowel cancer arises from the action of poisonous chemicals in the gut. And, although research is still at an early stage, there is some evidence that probiotics may reduce levels of these. However studies in humans have been contradictory.
Do you need probiotics?
So should we all be using probiotics on a daily basis? The answer is not really, according to Professor Nicholson. "The idea that we should all be taking them is ill-founded," he says, "although in certain cases they can be very useful." The reason? We all have a unique microbial fingerprint so probiotics don’t affect us all equally and strains that may benefit some of us may have no effect on others.
As Professor Nicholson points out, "Probiotics may or may not be useful and they can have different effects on different people." However he adds, "They can be helpful if you have a gut problem or problems such as pancreatitis and/or liver disease."
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How ageing affects our gut microflora
As we get older age-linked changes in, for example, immunity and how long it takes food to pass through our gut (something known as 'transit time') can affect the composition of bacteria in our gut. "The gut microflora are very different in a 60-year-old to a 30- or 40-year-old," observes Professor Nicholson.
According to some experts, these changes may make us more vulnerable to infections and age-related problems such as obesity, diabetes, and certain sorts of cancer.
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The difference between probiotics and prebiotics
Although research is contradictory on probiotics, prebiotics appear to be more promising in establishing the optimum balance of gut microflora. These are non-digestible complex carbohydrates found in foods such as:
- whole grains
They include components called fructooligosaccharides (FOS), inulin and galactooligosaccharides (GOS). As well as being present naturally in a wide range of foods they can also be found in fortified foods and in capsules, tablets or powders that you sprinkle on food.
Prebiotics provide the ‘food’ for probiotics to feed on. Studies have shown they can help enhance our absorption of minerals such as calcium and magnesium. There is also research on their potential to combat inflammatory bowel diseases, such as Crohn’s disease, and to be beneficial for people with IBS, heart disease, obesity, diabetes and even bowel cancer. There is also emerging evidence that they can strengthen immunity and increase our resistance to infection.
"Because they encourage several different types of bacteria they may be more effective than probiotics. And combinations of pre- and probiotics – what we call synbiotics – may be even more powerful," explains Professor Nicholson.
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Treatment for digestive disorders
For the moment however the jury is out. If you have a gut problem such as IBS or one of the inflammatory diseases you could try taking a pre and/or probiotic and take it once to check that there are no adverse side effects, such as diarrhoea. If there isn’t, try it for a bit longer to see if you feel better. If you don’t, you may want to try a different product. When choosing which product to take it’s best to go for one of the big, well-established brands as they have more of an interest in making sure that any claims they make stand up.
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