THE GREAT CONTROVERSY: TRIALS INVOLVING IBS

Irritable bowel syndrome or IBS is a disorder characterized by chronic diarrhoea or constipation, or a mixture of the two. (Chronic in medical parlance means ‘long-term’.) In most patients, there is also abdominal pain.

A major trial of IBS patients was carried out at Addenbrooke’s Hospital, in Cambridge, by Dr John Hunter and Dr Virginia Alun-Jones. Twenty-one patients were involved, and they were placed on a diet of nothing but lamb, pears and water for the first week. Other foods were then reintroduced one at a time. Fourteen of the patients – 66 per cent – improved considerably on the diet and were then able to identify culprit foods. Eleven of these patients were later tested double-blind to check that the effects were not purely psychological. Normal-sized portions of the food were eaten, disguised in a strong-tasting lentil puree that effectively concealed the identity of the food. All the patients responded in much the same way as they had done when they could taste the food being tested.

One obvious criticism of this trial is that the numbers involved were small. However, Dr Hunter and Dr Alun-Jones followed it up with another trial involving 122 patients. The percentage who responded to the diet was slightly higher – about 70 per cent. When a follow-up questionnaire was sent out, two to three years later, 86 per cent of patients replied, and 87 per cent of those who replied were still following the diet and benefiting from it.

In another trial of IBS, although there was a response to an elimination diet, the percentage who benefited was much smaller. This study was carried out by Dr David Pearson and Dr Stephen Bentley of the University Hospital of South Manchester, and Dr Keith Rix, a psychiatrist at the University of Manchester. The patients had all been referred to an allergy clinic at the hospital, because they suspected that their bowel symptoms were caused by food.

Nineteen patients completed the diet, and 14 of these showed an improvement in their symptoms. When tested with foods, ten produced consistent reactions to foods, while four did not.

At this stage, two patients with consistent reactions dropped out of the study, so only eight were left. They were tested double-blind with food in capsules, and five of them failed to react to foods that they had previously identified as causing problems when they could taste the food. This left just three whose bowel symptoms could definitely be related to food – only 15 per cent of the number who took part. Some of the patients were diagnosed as having mild psychiatric disorders, and this led the doctors involved to conclude that psychosomatic problems were an important factor in causing the symptoms for the remaining 85 per cent.

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