IBS and Food Allergy/Hypersensitivity
By John D. McGuire
Irritable bowel syndrome (IBS) is a common, debilitating, multi-factorial, functional gastrointestinal disorder where a definitive aetiology has not been established and no uniformly successful treatment exists. The condition is very prevalent in developed countries with IBS symptoms experienced by 8-22% of the population. (1)
IBS is characterised by a combination of symptoms and signs, such as abdominal pain, constipation (IBS-C), diarrhoea (IBS-D) — or alternating between both (IBS-A) — a noted change in both the frequency and consistency of stools, rectal mucus due to hyper-secretion of colonic mucus, dyspeptic symptoms including anorexia, flatulence, gastro-oesophageal reflux (GOR) and nausea, and an emotional component where anxiety and/or depression are often noted. Abdominal pain is often relieved following defecation. . Originally, diagnosis for IBS was made based on the Rome I Criteria. This previous criteria specified that there should be at least 3 months of abdominal pain, either continuous or recurrent, that is relieved by defecation &/or is associated with either a change in the frequency or consistency of the stool. Conversely, the Rome II Criteria differs from that of the Rome I in that it specifies that the abdominal pain should be present either continuously, or recurring for a period of 12 weeks or >. Both the Rome I & Rome II Criteria are consistent in their description of what constitutes accompanying symptoms, i.e., relief of abdominal pain following defecation, &/or associated changes in both the frequency & consistency of the stool, but the Rome II Criteria is more specific in stipulating that at least 2 of these accompanying symptoms must be noted, along with abdominal pain. Although the Rome I Criteria was also quite detailed in specifying that an individual had to have two or more associated symptoms of IBS, e.g., altered stool frequency of more than 3 per day or < 3 per week; abdominal distension; bloating; passage of mucus, etc, > 25% of the time, the newer Rome II Criteria has helped in simplifying the diagnosis of IBS. Where patients are <45 years of age, & they meet three or more of the Rome II diagnostic criteria (without ominous symptoms), a confident diagnosis can be provided without the need for invasive testing.
Rome III
Recently, there has been a further change, and that is the new Rome III criteria.
According to this latest criteria, IBS is defined as recurrent abdominal pain or discomfort for at least 3 days per month during the previous 3 months associated with two or more of the following symptoms: improvement with defecation, onset associated with a change in the frequency of stool and/or onset associated with a change in form or appearance of stool. (2) Defined simply, symptoms are now recommended to originate 6 months prior to diagnosis and be currently active (i.e., meet criteria) for 3 months. This time frame is less restrictive when compared to Rome II (12 weeks of symptoms over 12 months) and is easier to understand and apply in research and clinical practice. (3)
Food allergy/hypersensitivity
Food allergies and/or sensitivities are an IgE-mediated immunological response to foods that release inflammatory mediators, whereas food intolerance is a non-immunologically mediated adverse reaction. Although the use of IgE RAST or skin-prick testing might prove positive to a number of foods in IBS patients, other researchers have proposed testing for IgG antibodies to exclude food sensitivity. A correlation between raised IgG antibodies and foods known to exhibit a sensitivity response in IBS patients has been demonstrated. (4) This study demonstrated that by eliminating all foods in which a prior sensitivity was detected and demonstrated by raised IgG antibodies resulted in a significant improvement in IBS symptoms. Further studies examining the effects of foods capable of raising serum IgG levels in IBS patients suggest IBS may be related to an immune response (5-7)
Food intolerance
Studies have been conducted to determine whether intolerance to specific foods can result in IBS. (8, 9-11, 12-14) Of thirty five different food items, the principal foods reported by participants implicated in development of IBS symptoms included cabbage (57 per cent), onion (56 per cent), peas/beans (46 per cent), hot spices (45 per cent), deep-fried food (44 per cent), coffee (39 per cent) and cream (37 per cent). The major symptoms reported were gas problems, pain, postprandial dyspeptic symptoms, and abdominal discomfort. Furthermore, the results support current opinion that not all IBS patients benefit from an increase in dietary fibre. However, reports discount the impact of foods on aggravating the symptoms in IBS patients. (15, 16, 17) This reaffirms the discrepancies seen throughout the literature concerning dietary modifications, which understandably leads to confusion as to what foodstuffs should be excluded in treating IBS patients.
Sorbitol and xylitol
Sorbitol and xylitol are artificial sweeteners found commonly in many food items. (18) Unlike glucose, intestinal absorption of xylitol is slow (19, 20) and in the presence of increased motilin levels, intestinal transit time is decreased. Furthermore, large doses (>30 g) of xylitol can produce diarrhoea in most healthy individuals. (21) Large doses of sorbitol can induce osmotic diarrhoea, bloating and pain (22, 23) and therefore it is possible that smaller doses might aggravate symptoms in IBS patients, particularly those who are diarrhoea predominant.
Fructose
Studies have identified a possible correlation between fructose intolerance and many IBS symptoms, such as altered bowel frequency, bloating, flatus and pain. IBS patients who tested positive following a fructose breath test, and limited their daily fructose intake, had their symptoms improve significantly. (24,25) Abnormal colonic fermentation has been noted in IBS patients (26) thus, it is feasible that fructose malabsorption within the small intestine might lead to an increase in symptoms if fructose is fermented in the large intestine by the action of colonic microflora. (27)
Fat
Increases in the dietary lipid content causes an increase in small-intestine motility, and the gastro–colic reflex response in IBS patients has been noted as prolonged and exaggerated, leading to exacerbation of gastrointestinal symptoms in IBS patients. (28- 29) However, dietary lipids inhibit intestinal gas transit, and this mechanism is up-regulated in IBS patients. (30)
Lactose
The symptoms of lactose malabsorption (bloating, osmotic diarrhoea) are similar to those of IBS, suggesting that lactose may be a dietary cause in some individuals. Without the enzyme lactase, lactose cannot be hydrolysed in the small intestine and thus could be fermented in the colon. (31) It is also possible that alterations to colonic micro-flora might be involved in the development of IBS in lactose-intolerant individuals. Low-grade inflammation of the colon, and also the effects of post-infective enteritis, might be a cause of lactose intolerance in some IBS patients. Lactase function decreases with inflammation, but generally can regenerate within 1–2 weeks following an episode of enteritis. (32)
Gluten and gliadin
In one study, 35 per cent of IBS-D-predominant patients with suspected coeliac disease were found to be HLA genotype-DQ2-positive, and 23 per cent had increased intra-epithelial lymphocytes. (33) In this group of patients, symptoms significantly improved after a six-month period on a gluten-free diet. Intestinal IgA levels and stool frequency decreased significantly in those IBS patients who demonstrated a positive response to both markers (HLA-DQ2 and intestinal antibody) compared to IBS patients who tested negative. As oat and rye both contain gliadin, avoidance of these foods, as well as wheat, might benefit IBS-D-predominant patients in whom these markers are shown to be positive. (34) To confirm the involvement of such proteins, testing specifically for IgG and IgA to gliadin would seem a logical first step, thus, establishing a clear diagnosis of either coeliac disease or IBS.
Coffee
IBS symptoms are largely associated with intestinal smooth-muscle activity. Coffee is well known to stimulate gastric and intestinal smooth-muscle activity (35) and thus may be a contributing factor in IBS-D individuals. However, decaffeinated coffee may contain approximately one per cent caffeine, and thus IBS-D-predominant patients should avoid both caffeinated and decaffeinated coffee. (36)
Alcohol
Hydrolysable tannins, as found in red wine, are astringents (causing contraction of mucous membranes and reducing secretion of mucus). (37) Thus symptoms experienced by IBS-C and IBS-A patients may be exacerbated by the consumption of tannin-containing beverages, as the tannins may contribute to an increased transit time. Furthermore, tannic acid reduces peristalsis, and high tannin-containing foods may contribute to the constipation seen in both IBS-C- and IBS-A-predominant individuals due to their binding effect. (38)
Conversely, Dapoigny et al (39) state, that ‘alcohol is known to induce diarrhoea in abusers through a potential neural mechanism, thereby decreasing transit time’. As IBS-D-predominant patients already demonstrate a decreased transit time, it might again be logical to exclude alcoholic beverages from the diet, despite the sometimes contradictory findings in the literature.
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