Gut reaction

There’s no denying the lure of those ads, showing stressed and bloated people gulping a bottle of ‘friendly bacteria’ and suddenly breakdancing at the bus stop.

And the ads seem to be doing the trick – sales of probiotic drinks have doubled in the past two years. But what are these so-called friendly bacteria, and can they really offer the health benefits the ads suggest?

Probiotics are harmless bacteria which occur naturally in the large intestine, where they help stop pathogens entering the bloodstream. But factors such as stress, poor diet, taking antibiotics and food poisoning can deplete them – with results that can range from diarrhoea to irritable bowel syndrome.

The theory is that by topping up existing friendly bugs with a probiotic product, conditions in the gut are improved, helping with digestive problems and, as a result, the immune system as well. But while this idea is nothing new – a Japanese researcher identified probiotics in 1935 – it’s only in the last few years that the UK has seen a dramatic increase in the purchase of food and drinks enhanced with friendly bacteria. Most of the products on the market – which include drinks, cheese, mints and juices – contain one or both of two strains of bacteria, lactobactillus acidophilus and bifidus bacterium.

And there is certainly evidence that probiotics work. Research by Swedish scientists has found that a daily probiotic drink can boost the immune system, while Dundee University showed that patients with ulcerative colitis suffered less pain and diarrhoea after taking friendly bacteria. “Probiotics can protect against diarrhoea and aid recovery from antibiotics, among other benefits,” says Glenn Gibson, professor of microbiology at the University of Reading.

But according to the Drug and Therapeutics Bulletin, research has not yet proved that probiotics boost general wellbeing as claimed, and that some can be killed off by stomach acids before even reaching the gut. One study estimated that 90 per cent of one probiotic bacteria was killed by stomach acid, meaning that a drink needed to contain a least one billion of the bugs to be useful.

While most brands have measures to ensure that the correct ‘dose’ of good bacteria is produced, others do not. For this reason, Professor Gibson suggests:  “You need a lot of bacteria for a product to have any effect – at least 10 million bacteria in every 1ml,” he says. “If you can’t find how much bacteria it contains on the label, call the manufacturer’s helpline."