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Reviews of Peter York’s new book about the evolution of the Sloane Ranger suggests that its habitat is changing. The unreconstructed Barbour-and-tweed clan is now found predominantly in the country, and when spotted in Chelsea it is usually because it has been blown off-course by an ill wind. The last time a flock of Sloane Rangers in their true plumage was seen en masse in London was on the Countryside March in September 2002.

Sloane Rangers, according to York, have changed. They are now like birds that change their feathers according to the time of the year and their environment. London Sloanes have become urban merchant bankers and hedge-fund directors rather than country squires. Few Sloanes reared in their traditional breeding grounds can now live a relatively trouble-free, financially secure and active social life in the smarter districts of London without working hard for long hours.

In the early1980s, when the first book about Sloanes was published, their financial worries were often confined to how much Uncle Henry would leave in his will rather than mergers and acquisitions. Now Sloanes live as harried and hurried a life as their neighbours. Could their guts be taking the strain? Perhaps. The increase in the incidence of irritable bowel syndrome (IBS) now accounts for more than half of all cases referred by GPs to consultant gastroenterologists for a specialist opinion. Although IBS affects both sexes, it is three times more common in women than in men.

Irritable bowel syndrome is described as a motility disorder that alters the behaviour of the muscles in a patient’s guts. It involves the small and large bowel and causes a variable amount of pain, and either, or both, diarrhoea and constipation. The diarrhoea may be of sudden onset, either after eating or in the early morning. The troubles that IBS causes are associated with such trying symptoms for a party-loving Sloane as bloating, wind, flatulence, nausea, headache and tiredness.

Irritable bowel syndrome may be triggered in women by their periodic hormonal changes, and in both sexes by tiredness, stress – especially stress when eating, emotional turmoil, an unwise choice from a menu or merely eating too much. Too hefty a dose of alcohol before going out in the evening so as to appear relaxed by lessening the tensions of the office may make the situation worse.

Anyone writing on medical matters has to cross poorly charted minefields studded with charges primed to explode in the face of an author who writes on a contentious subject. Few mines are as easily set off as those concerning IBS. The debate on the relationship between food intolerance and IBS is an especially tricky subject. Patients, doctors and commentators agree that IBS can be associated with emotional tension or a recent gut infection, but the suggestion that food intolerance can also be the cause is controversial for some reason. Most patients find that they can tolerate many foods when eating alone, or at home, but when at a social occasion the same food may induce an attack.

Some foods are blamed regularly. These include fatty foods, such as foie gras, richly spiced ones, including curry, onions, garlic, chilli, coffee and some alcoholic drinks. Discussion ranges around foods such as wheat, maize, dairy products, coffee, tea, cashew nuts, citrus fruits and broccoli and whether these alter the immune antibody response and the patient’s IgG and IgE antibody titre (quantity). Similarly, although Crohn’s disease is an autoimmune inflammatory bowel disease and not IBS, the role of diet in making it worse is also under investigation.

Research is being undertaken to find better ways of investigating links between IBS and food intolerance. Commercial kits from York Laboratory are available. But of those who show a positive result not all are necessarily related to diet.

Dr Anton Emmanuel, the director of the physiology unit at the University College Hospital, London, is an expert on inflammatory bowel diseases and irritable bowel syndrome and their possible association with food intolerance and antibody levels. He has shown that there is a significant association between patients’ observations on food intolerance and their overall antibody titres, but also that these can’t be correlated with certainty to any particular foodstuff.

Dr Emmanuel is now carrying out further trials in irritable bowel syndrome in which the selection of the control group and the diets of the people taking part in the experiment will be tightened so as to ensure randomisation, the exclusion of possible confounding problems in double-blind food challenge trials.

Meanwhile, patients with IBS should choose bland food from the menu, not eat too much or too rich foods and try to avoid eating when stressed, whether this is related to dinner with their boss or someone they lust after.

York testing: Tel 0800 458 2052 or visit www.yorktest.com

Cooler, Faster, More Expensive: The Return of the Sloane Ranger by Peter York and Olivia Stewart-Liberty, Atlantic, £19.99