Eating, especially fatty foods, triggers functional abdominal pain in around three of four people with IBS, it is important to distinguish this generalised intolerance to food from intolerance to specific foods, which may produce symptoms in certain individuals IBS and diet.

The role of true (specific) tolerance as a cause of the IBS is debatable, true food intolerance is an adverse reaction in the intestines to a particular food and will occur every time a person eats that particular food, one example of this is excess gas and diarrhoea as a result of lactose intolerance (inability to digest the sugar in milk).

Food allergy, by contrast brings on immediate symptoms whenever the individual eats the trigger foods, such as strawberries or oysters. These allergic symptoms may involve the digestive system (such as vomiting), but they often affect other parts of the body causing a rash, an attack of asthma or a running nose

Food tolerance: studies were made that tested people 's response to individual foods by excluding them from the people with IBS and diet plan completely, and then reintroducing them one at a time, these studies found specific food tolerance in between a third and two- thirds of people with IBS, the most common intolerance reported in the UK is to wheat, followed by Dairy products (especially cheese, yoghurt and milk), coffee, potato, corn, onions, beef, oats and white wine.

Some people develop typical IBS symptoms such as bloating, cramps and diarrhoea after eating carbohydrates that they are unable to absorb. Examples are lactose (milk sugar) and fructose (fruit sugar), if they are not absorbed, they may ferment in the gut and produce gas. Excluding these from IBS and diet can reduce symptoms and also reduce colonic gas production.

This suggests that changing what you eat can affect the fermentation resulting from the action of bacteria in the colon, reduced production of lactase- an enzyme that breaks down lactose ""in the lining of the small intestine can develop in adults and is relatively common in the UK, it is estimated to affect 10 per cent of those of northern European descent, rising to 60 per cent in people of Asian origin and 90 per cent of people of Chinese descent.

People taking a substantial amount of lactose (equivalent to more than half a pint of milk a day) can expect to benefit from lactose restriction. On the other hand, those with lower lactose intakes may not because a low intake does not usually cause symptoms of intolerance.

Elimination diets : a initial study using elimination diets ( that is diets that exclude all but a single type of fruit, a single type of meat , a single vegetable, and so on ) improved symptoms in two- thirds of those who completed the study.

The more practical elimination of food for people with IBS and diet control can impose less drastic restrictions on what you can eat, have been developed, these exclude only foods that are commonly implicated in food intolerance , these diets have a lower success rate ( around 50 per cent ) but are easier to follow.

Whether diets for food intolerance are really worthwhile is hard to assess, this is because of the placebo response (in which you feel better just because you are expecting to). Such an effect cannot be ruled out unless foods are given in such a way that neither you nor the researcher knows what you have just eaten when your response is assessed.

Even if you were to be given nothing but blended foods through a tube passing from your nose into your stomach, it is still impossible to assess any particular influences; examples of such influence are the role played by the important social, psychological and physical aspects of eating. These are likely to be at least as significant as the direct effects of individual food on the gut, interestingly; however, a study in which people were fed in this way with suspect food reported that 6 of 25 people with IBS correctly recognised that they had been given one of the foods that seemed to trigger their intolerance.

Specific food intolerance does appear to be the cause of symptoms in a small number of people with IBS, if your doctor suspects that this may be so in your case, you should ideally be referred to a specialist centre for objective, scientifically controlled tests. An enthusiastic, determined approach is required by everyone involve you, the doctor and dieticians because these studies need to be conducted for a number of weeks or months.

Food allergy: true food allergy is much less common than food intolerance and is usually not difficult to recognise, this is especially
on when eating particular food (or foods), it is associated with a rash, asthma or a running nose.
Such allergies often give a high incidence (70 per cent) of positive results to allergy tests such as skin- prick and blood tests. If you have this type of allergy, you are more likely to see a specialist in immunology rather than a gastroenterologist because your doctor is unlikely to think that you have IBS.

One study tested people with purely intestinal symptoms, it found that only 15 of 88 people who believed that they had food allergy had this confirmed in a trail in which neither they nor the tester knew what food they were eating, skin ""prick tests are more likely to be positive if your symptoms come on immediately after eating the suspect food than if they develop only some hours later.

Women and IBS and diet: although men and women in general are equally likely to develop IBS, studies have shown that women tend to consult their doctor more often than men, anxiety, depression and stress are known to occur more often in women, and this may play a part in triggering symptoms, it is also possible that hormonal differences may contribute to the differences between the sexes. During menstruation for example IBS symptoms of abdominal pain, diarrhoea and gas tends to get worse in 50 per cent of women.

Women with IBS are also more likely than men to show increases sensitivity of the gut and three times more likely than men to develop IBS after a gastrointestinal infection.

In 60 per cent of women with IBS, pain may also sometimes be felt deep in the pelvis following intercourse. It can come on several hours after intercourse, particularly when the women has constipation

The only way to know for sure if a food is a trigger for your IBS and diet is to try an elimination diet. An elimination diet involves tracking foods you suspect may trigger your IBS and cutting them out of your diet entirely for a period of time.