Food Intolerance - True food allergy is mediated by the immune system and is associated with hives, asthma, eczema, nasal discharge, and positive skin prick, RAST scores, or other allergy . However, food intolerance, rather than true food allergy, is believed to be more significant in . Between 33-66% of IBS patients report having one or more food intolerances. The most common culprits are dairy (40-44%) and grains (40-60%). The resulting gastrointestinal bloating, flatulence, and pain caused by this reaction appears to be mediated by inflammatory prostaglandin synthesis.
Neurochemical Imbalance - Interaction between the brain and the gut occurs via nerves that send neurotransmitter signals. An imbalance between two of these neurotransmitters, serotonin and norepinephrine, are implicated in IBS. Constipation may result when levels of norepinephrine increase, causing a reduction in serotonin levels and inhibition of another neurotransmitter called acetylcholine. Conversely, diarrhea can occur when increased serotonin inhibits norepinephrine and causes levels of acetylcholine to increase. For IBS patients, such an imbalance in the nervous system can lead to the fluctuating bowel symptoms of constipation and diarrhea.
History of Analgesic Use - Use of acetaminophen, a common pain-relieving medication, is associated with diarrhea-predominant IBS. Its action may be due to an imbalance in the neurotransmitter serotonin. Since acetaminophen can cause elevated levels of the serotonin by-product 5-HIAA in the urine, it is possible that acetaminophen somehow interferes with serotonin metabolism. Plasma serotonin levels have indeed been shown to be elevated after eating in patients with diarrhea-predominant IBS. Clinically, a drug that blocks the 5-HT3 serotonin receptor (5-HT3 receptor antagonist) is effective for women with diarrhea predominant IBS. It is interesting to note that asthma, another condition associated with disordered smooth muscle function, was recently found to be associated with acetaminophen.
Reproductive Hormones - IBS occurs more than twice as frequently in women than in men and tends to follow a cyclic pattern, with aggravation during the postovulatory (progesterone-dominant) and premenstrual phases of the menstrual cycle. Progesterone is known to delay gastric emptying and cause constipation; constipation with straining and the frequent passage of hard stools is a more prevalent IBS manifestation in women, especially during the postovulatory phase. At the end of the postovulatory phase, the sudden withdrawal of progesterone that occurs with the start of the premenstrual phase may trigger increased bowel activity. Women frequently report loose stools and diarrhea before or with the onset of menstruation. In contrast to progesterone, estrogen has not been associated with exacerbations of IBS symptoms.
In one study, high levels of luteinizing hormone (LH) were found in women with IBS; drugs that decreased LH levels and consequently suppressed ovarian production of estrogen and progesterone resulted in significantly improved IBS symptoms. LH is a reproductive hormone responsible for the production of testosterone in males and estrogen and progesterone in women. In men, the opposite result was found: low LH and low testosterone tended to be associated with IBS symptoms. High LH therefore appears to cause exacerbations in women by stimulating progesterone and estrogen, yet have a protective effect in men.
Along with progesterone levels in women, prostaglandins E2 and F2 alpha also increase in the premenstrual phase. Since they are powerful stimulants of bowel contractions, it is possible that women with IBS may have an exaggerated response to these prostaglandins.
Mood - Anxiety, hostile feelings, sadness, depression, and sleep disturbance are associated with IBS. Adverse life events such as family death, marital stress, financial difficulties, and especially physical and sexual abuse, have also been reported more frequently in IBS patients than in the general population8. However, it is possible that IBS patients with this social or psychological background may be more likely to seek medical treatment or participate in research studies.
The impact of stress on bowel motility and pain were explored in one study by administering corticotrophin-releasing factor (CRF), a hormone released in the body during stress. CRF increases motility of the descending colon and can induce abdominal pain. The researchers found that IBS patients had greater colonic motility and more abdominal pain after receiving CRF than controls.
Antidepressants have been shown to be very effective for treating bowel motility and visceral nerve responses, in addition to addressing the emotional component of IBS.
Small Intestine Bacterial Overgrowth - Excess bacteria in the small intestine, an area that is normally relatively free of bacteria, is being recognized as important in the development of IBS. When these bacteria are present in the small intestine, excessive gas, bloating, abdominal distension and pain, and altered gut motility can result.
Causes of small intestine bacterial overgrowth include decreased gastric acid secretion (possibly due to natural aging, stomach ulcer, and colonization by helicobacter pylori bacteria), decreased bile flow, or decreased pancreatic enzymes with poor absorption of carbohydrates, fats, and proteins. The resulting undigested and unabsorbed carbohydrates in the small intestine and colon cause excess fermentation and encourage growth of unwanted bacterial species. An abundance of gas is produced, as well as short-chain organic acids such as lactic acid, which can damage the mucus lining of the intestines and further aggravate carbohydrate malabsorption. In addition, putrefaction of proteins in the small intestine produces substances called vasoactive amines that can affect intestinal muscles. |
