Another important causative factor in IBS may be the gut flora – the menagerie of bacteria and yeasts that live in our intestines and are harmless, or beneficial, in most people. Research done by Dr John Hunter at Adden-brooke’s Hospital in Cambridge suggests that many IBS sufferers have a disturbed gut flora: some bacteria or yeasts are over-represented while others are lacking.

A severe bout of diarrhoea, or prolonged use of antibiotics, could start the problem off, by removing many of the beneficial bateria from the gut – their place could then be taken by others. This would explain why some people date their IBS to a bad attack of food poisoning, prolonged use of antibiotics for acne, or a hysterectomy operation.

If this idea is correct, the actual trigger for the diarrhoea would probably be toxins produced by the bacteria that are over-represented. However, these results have been obtained in patients who also have specific reactions to certain foods, which trigger off their IBS symptoms. How these food reactions and the gut flora disturbances might be related is a tricky question, and one which Dr Hunter is currently investigating – he believes that the ‘abnormal’ bacteria feed on particular foodstuffs, making the patient appear intolerant of these foods. Enzyme deficiencies may also be involved.

There are various other ways in which adverse reactions to foods might bring on diarrhoea and pain, but at present there is too little evidence to choose between them. In the end, it may turn out that several different factors are at work.

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