The patients included in the present study all complained of food hypersensitivity because they perceived their symptoms as being food induced. Although a causal relationship between food intake and symptom development cannot be ascertained from the present study, we consider the possibility that so many patients are simply “misattributing” as rather unlikely, for several reasons: The patients experience daily deteriorations after eating. Most often it is bread, milk, and fruits that are accused as the culprits. Bloating, a common symptom, is typically gone in the morning, but worsens during the day after eating. In the absence of food [15
], or when eating well-tolerated food items only, bloating is much less pronounced. Some of the patients (19%) had on their own initiative started and continued with a gluten-free diet. This is a controversial, but reasonable action according to a recent study: In a double-blind randomized placebo-controlled trial, Biesiekierski et al. showed that gluten indeed can provoke IBS symptoms in subjects without celiac disease [16
]. In earlier studies, we have shown that lactulose, a non-absorbable, but fermentable carbohydrate, can replicate the patients' complaints [17
], and Gibson et al. have shown that a number of poorly absorbed short-chain carbohydrates do the same [18
]. Most likely, therefore, the symptoms are in some way induced by the intake of particular food items [19
]. Consistently, food has recently been denoted as “the forgotten factor” in IBS [20
], and further investigations are clearly warranted.
It is often difficult for patients to explain IBS symptoms during a few minutes' consultation, and questionnaires might be of great help. Many patients dislike talking about their bowel habits and therefore use single words such as diarrhea, constipation, or pain solely. But these words are often partly incorrect. “Pain” in patients with IBS is often more a feeling of discomfort, and diarrhea and constipation are usually a combination. “Incomplete evacuation” is often misunderstood and often denoted as “diarrhea” because of frequent visits to the toilet. However, increased fecal volume and bowel movements at night, that is, characteristic features of secretory diarrhea, are rarely seen in these patients. Therefore, several visits to the toilet a day are in itself an indication of incomplete evacuation, or so-called pseudo-diarrhea. Such communication problems, and also the experience of not being believed with respect to their own explanatory models, often make the patients embarrassed. Interestingly, the IBS-SSS questionnaire performed very well in this context. The two last questions are about how dissatisfied the patients are with own bowel habits and how much this influences their lives. Here, most of the patients scored very high without hesitation.
The present study indicates that many patients with perceived food hypersensitivity suffer from severe systemic symptoms in the form of musculoskeletal pain and/or chronic fatigue in addition to IBS. Thus, 71% of the patients had the complete “triad” of IBS, musculoskeletal pain, and chronic fatigue. The musculoskeletal pain problems seem to comply with the diagnosis of fibromyalgia [1,2
]. Approximately half (54%) of the patients with joint pain experienced morning stiffness in the joints, which typically lasted 1–2 h. All patients with joint pain also had fatigue, but not all patients with fatigue had joint pain. Thus, clinically significant fatigue was seen in 85% of all patients, and 78% of those with fatigue also had joint pain. The FIS and the FFS questionnaires showed very comparable results, even though they measure slightly different aspects of fatigue: while FIS is a measure of the patients' perception of the impact of fatigue on their lives [21
], FFS is a measure of the doctor's assessment of severity of bodily aches and pain and of various dimensions of fatigue, including cognitive, autonomic, and sleep disturbances, headache, and influenza symptoms [12
]. Our cut-off levels for diagnosing clinically significant fatigue are arbitrary, based on individual evaluations. The regression line in crosses the Y-axis above zero, indicating that the doctor tended to score weaker symptoms higher than the patients. An apparent reason for this could be that in milder cases of fatigue, the patients often had their own measures to combat symptoms and only reluctantly admitted that they still had problems. However, our patients' scoring of the impact of fatigue is on average at a level comparable with that reported previously in patients with the chronic fatigue syndrome [11
]. Patients with the highest scores were severely physically impaired, and some reported staying mostly indoors. However, since this is an outpatient material, none were totally bedridden.
In our patients, local and systemic symptoms go hand in hand, sometimes clearly in response to the intake of particular food items. We have long observed that patients undergoing the lactulose breath testing may complain of freezing during the examination. A more systematic recording of the problem revealed that more than half of the patients experience what some denote as “inner freezing,” starting approximately one hour after drinking lactulose 10 g dissolved in 200 ml of water. A few patients even experience severe relapse of both intestinal and extra-intestinal symptoms lasting for several days (unpublished observations). Because lactulose is metabolized by microbes within the intestines, disturbances of the gut microbial flora leading to “malfermentation” may be an important pathogenetic mechanism [22
BMI of the patients was relatively high, on average 23.5, and completely independent of bowel habits. Totally, 25 (30%) of the patients were overweight (BMI >25). Mild intestinal malabsorption of fat was seen in 10 of 38 cases, consistent with findings in an earlier study of patients with post-infectious IBS [23
]. The results suggest a component of intestinal malabsorption in IBS. But even the cases with fat malabsorption were not slim (BMI on average 24.0, range 18.1–29.4). This apparent paradox of malabsorption combined with relatively high body weight is an interesting finding that deserves further investigation.
The present study is based on a selected hospital material, which may not be representative for subjects with IBS in general. However, a high prevalence of systemic symptoms in patients with IBS has also been noted in the general population. Johansson et al. found that estimated costs for health resource use among patients with IBS in general practice were largely explained by comorbidities [24
]. Thus, the impact of systemic symptoms in patients with IBS may be greatly underestimated.
Our study was performed at a gastroenterological department, a fact that might have contributed to a special selection of patients. However, the patients were very similar to those studied earlier by an interdisciplinary team at an allergological department [7
]. Logically, most of the patients asked whether they were food allergic, and as observed previously [13
], atopic diseases were prevalent among the patients albeit food allergies as a cause of the patients' symptoms were not demonstrated. Others have found indications of low-grade intestinal and systemic inflammation in patients with IBS [25
]. The cause is not known, and it is tempting to speculate that atopic disease and low-grade inflammation, as well as the whole cluster of gastrointestinal and systemic symptoms, might be consequences of an underlying intestinal dysfunction related to the fermentation of undigestible food ingredients [7
]. Interestingly, immuno-modulating biological therapies have recently been shown to be beneficial in some patients with chronic fatigue syndrome [26,27
]. An initiating disturbance within the intestines is consistent with the fact that many of our patients reported a long history of IBS before the appearance of musculoskeletal pain and fatigue, and several reports by others suggest that post-infectious IBS may precede the development of fatigue [7,28,29
]. Psychopathology is often associated [30
], but do not explain the burden of somatic symptoms [8
]. More likely psychological disturbances are also a consequence rather than a cause – in a way similar to what previous studies have shown to be the case in patients with peptic ulcer disease [31