"IBS and diet
Both the act of eating and the type of food being eaten has been linked to IBS symptoms.
Eating is the first step in the digestive process. It causes contractions or spasms of the colon. The healthy response is an urge to have a bowel movement within an hour after a meal. Those who have IBS might instead have an immediate and severe urge to have a bowel movement.
Certain foods also have been linked to IBS symptoms. Fatty or greasy foods, dairy products, chocolate, alcohol, caffeine, carbonated beverages, orbital and gas-producing foods (e.g. beans, broccoli, cabbage) are common foods that IBS sufferers may find worsen their problem. Some people find it's helpful to keep a journal of their eating habits and symptoms, in order to identify and avoid problem foods. "http://www.themonroe...om/c0612hea.htm
How you can have symptoms right after eating.
"The gastrocolic reflex, a partly neurogenic process, refers to an increase in colonic motility induced by feeding. Postprandial deviations from the normal motility patterns lead to altered bowel habits. For example, a spastic colon (eg, diarrhea-predominant IBS [D-IBS]) is characterized by an exaggerated motility response to food intake.
This exaggerated postprandial response also occurs in response to intraluminal distention or to an injection of cholecystokinin (CCK -- a hormone released in the duodenum) in patients with IBS."
Researchers have found that the colon muscle of a person with IBS begins to spasm after only mild stimulation. There are two “sets” of muscles in the colon, longitudinal and circular, and the one that spasms with more force leads to the symptom of either diarrhea or constipation. The person with IBS seems to have a colon that is more sensitive and reactive than usual, so it responds strongly to stimuli that would not bother most people."
Ordinary events such as eating and distention from gas or other material in the colon can cause an overreaction in the person with IBS.
Certain medicines and foods may trigger spasms in some people. Sometimes the spasm delays the passage of stool, leading to constipation.
Chocolate milk products or large amounts of alcohol are frequent offenders and can trigger attacks.
Caffeine causes loose stools in many people, but it is more likely to affect those with IBS.
Researchers also have found that women with IBS may have more symptoms during their menstrual periods, suggesting that reproductive hormones can increase IBS symptoms."
"Diet, Stress and IBS
Many people report that their symptoms occur following a meal or when they are under stress. Eating causes contractions of the colon. Normally, this response may cause an urge to have a bowel movement within 30 to 60 minutes after a meal. In people with IBS, the urge may come sooner and may be associated with pain, cramps and diarrhea. One reason may be the gastrocolic reflex. Gastric distension stimulates colonic activity to make room for an ingested meal. Volume, fat content and other more difficult-to-digest items make the gastric reflex more intense. With a spastic colon, there is an overreaction of this reflex. The colonic muscle stretch provided by fiber, such as cereal fiber, lessens this response.
The strength of the response is often related to the number of calories in a meal, and especially the amount of fat in a meal. Fat in any form (animal or vegetable) is a strong stimulus of colonic contractions. Many foods contain fat, especially:
Meats of all kinds.
Stress also stimulates colonic spasms in people with IBS. This process is not completely understood, but scientists point out that the colon is controlled partly by the nervous system. Behavioral-health counseling and stress reduction (relaxation training) can help relieve the symptoms of IBS. However, doctors are quick to note that this does not mean IBS is the result of a personality disorder. IBS is, at least partly, a disorder of colon motility and sensation. "