Irritable bowel syndrome (IBS) is one of the most frequent functional gastrointestinal disorders (FGID), defined by abdominal pain and abnormal transit conditions in the absence of detectable organic illness [1
]. Prevalence of IBS has been estimated to be approximately 11% in the general population [3
]. In France, the prevalence of IBS has been estimated at 4.7% (4.36–5.04%) [4
]. Among several factors suggested to be involved in the pathogenesis of IBS, diet appears to play a key role [5
]. Indeed, two thirds of IBS patients (70%) report adverse reactions to food, and 62% usually limit or exclude food items from their diet [5
]. Several studies have investigated the associations between food consumption and IBS, and the food items most commonly reported by the patients as worsening or triggering IBS symptoms are the following: milk, wheat products, fatty and fried foods, caffeine, specific vegetables (cabbage, onions, peas/beans), hot spices, and alcohol [5
]. Most studies usually study relationships between single nutrients or food components and disease, which does not allow capture of the complexity of a subject’s diet as nutrients or foods are not consumed individually but in combination in the food matrix. Comprehensive approaches involving the assessment of dietary patterns (DP) have therefore stirred considerable interest in the scientific community, as they aimed at understanding meaningful combinations of food consumption in the population [17
]. Moreover, assessing the relationship between DP and various health outcomes in different countries appears important as several factors, including different cultures, geography and religious beliefs influence the dietary patterns of different populations [19
]. A recent cross-sectional study performed in Iran focused on dietary patterns in relation to IBS [21
], but to the best of our knowledge, no such associations have yet been studied among western populations.
The objective of the present study was to identify a posteriori DPs and to estimate their associations with IBS in a large French study, the NutriNet-Santé study.
In the present study, PCA was used to identify main DPs and their relationship with IBS in a large French study. Among the three major patterns identified in our study population, IBS was associated with the “western” pattern in men and women, and with the “traditional” pattern in women after adjusting on covariates.
Both of these profiles were highly correlated with higher consumption of fatty foods (i.e., processed meat, animal fat, sauces, cheese, snacks). An association between a high-fat DP and IBS is in line with several studies which have highlighted that a large proportion of IBS patients reported their symptoms to be related to fatty food consumption [10
]. Excessive intake of lipids as an underlying pathway in the development or worsening of IBS symptoms has been widely studied and various mechanistic hypotheses have been identified, including enhanced colonic response to lipids [39
]. In normal conditions, intraluminal lipids increase perception of concurrent intestinal stimuli and modulate intestinal motor reflexes, and these effects are exaggerated in IBS patients [38
]. However, available data on differences in the patterns of fat intake between IBS patients and controls are inconsistent, suggesting that the effect of diet possibly depends on its overall composition, rather than on a single component [39
]. Moreover, “western” and “traditional” DP were both highly correlated with alcohol consumption an association with IBS that has been repeatedly highlighted [10
Our “western” profile was highly correlated with consumption of fat and sugared products including cakes, cookies and pastries, desserts, sweetened beverages, sugared cereals, and with salty snacks, sauces, starches and sodas. A cross-sectional study recently performed in Iran (population of 3846 participants) has shown that a “fast food” dietary pattern was positively associated with IBS in women [21
]. This dietary profile showed strong correlations with French fries, vegetable oils, meat, salt, pepper, and onions. The authors also identified a western profile, which showed no association with IBS in neither women nor men. A study performed recently in France among 380 women showed that the dietary clusters “unhealthy” and “convenience” were associated with a higher frequency of flatulence [45
]. Despite some differences, the “fast-food” profile identified by Khayyatzadeh and colleagues, and the “unhealthy” cluster of Holmes and colleagues have common features with our “western” DP, especially regarding the higher amount of fats and carbohydrates intake. Moreover, they all represent a trend towards globalization of diets at the world’s level [46
] (Tables S3 and S4
). In France, as in other industrialized countries, shifting DP characterises a dietary transition combined with lifestyle changes. These changes, resulting in a decline in energy expenditure, have been identified as significantly associated with disability and premature deaths due to chronic non-communicable diseases which include obesity, diabetes mellitus, cardiovascular disease, hypertension and stroke, and some types of cancer [49
]. These are partly due to higher energy intakes, increases in fat, and saturated fat intakes with higher animal source food consumption, lower intakes of fruits and vegetables, and the increase of additives and processed foods [51
Unlike the “western” DP, the “traditional” profile showed an important correlation with fruits and vegetables, representing a major source of dietary fibers which are used as levers for the improvement of IBS symptoms [54
]. It was also characterized by a lower proportion of pre-prepared or fast food products, which are considered risk factors for IBS [55
]. These two features could partly explain why the association we found was weaker than those obtained with the “western” profile. Moreover the results were not consistent across gender for this pattern. This could partly be due to several gender and/or sex differences in IBS. There is growing evidence of the multiple points in which sex may influence the GI tract and the brain gut axis, such as mood, stress, social role, sexual hormones, visceral pain perception, motility and even genetic and immunologic microbiome [56
]. Finally, our dietary patterns might differ from one another regarding their content in Fermentable Oligo-, Di-, Mono saccharides and Polyols (FODMAPs) or wheat. These are a particular type of carbohydrates that are poorly absorbed in the small intestine and can lead to increased luminal water retention and gas production [8
]. FODMAPs can be found in many foods, but are more specifically present in fruits and vegetables (fructose, fructans and polyols), milk and dairy products (lactose), cereals (galactans), and prepared food (polyols) [60
]. Considering this, differences in FODMAPs consumption (types and/or amounts) across DPs may partly explain our results.
The DPs we obtained in the present study are in line with those observed in previous cohorts in western countries. In the NHANES (National Health And Nutrition Examination Survey), Tseng and De Vellis identified two major DPs with PCA: the “Vegetable-fruit pattern” and the “Red meat-and-starch pattern” [64
]. Fransen and colleagues in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort and Hu and colleagues in the Health Professional Follow-up Study (HPFS) identified the same two dietary profiles: “prudent pattern” and “western pattern” [65
]. Schulze and colleagues in the EPIC cohort highlighted two profiles: ‘traditional cooking” and “fruits and vegetables.” In France, several DPs were identified across various studies in the SUpplémentation en VItamines et Minéraux Anti-oXydants (SU.VI.MAX) study, including “alcohol and meat products,” “prudent diet,” “health conscious,” “modern,” “traditional,” [32
]—and in the Epidemiologic prospective cohort study of women from the MGEN national insurance plan (E3N) cohort—“Prudent,” “Western,” and “Aperifif” [71
]. The “vegetable-fruit,” “health conscious,” and “prudent diet” patterns are similar to our “healthy” profile.
Since our patterns are similar to those of other cohorts conducted among western populations, the replication of this study within other western population samples would be useful to validate our results.
Our study had some strengths. First, to the best of our knowledge, this is the first study evaluating the association between DPs and IBS within such a large sample from the general population. Moreover, the identification of IBS was based on the Rome III criteria which was considered the gold standard at the time of inclusion [1
]. The prevalence of IBS in our study is in agreement with other studies conducted among the French population and using similar identification criteria (5%) [4
]. Finally, we used validated dietary collection data, using repeated and detailed dietary records [27
However, some limitations need to be considered. First, the cross-sectional design of the study does not allow us to infer causality. Furthermore, the time between both exposure and outcome assessments among participants is heterogeneous. Another limitation pertains to the fact that participants were volunteers. They were probably more likely to be health conscious and have more controlled diets, and therefore may be different from a representative sample of the general population regarding dietary behaviors. For this study we selected participants with at least 3 sets of dietary questionnaires. Since IBS status was defined according to declarative data from participants, we are therefore not able to exclude that some IBS patients have an organic digestive disease. Conversely, we may have excluded some participants with IBS, due to self-reported organic disease or alarm symptoms. Nevertheless, the prevalence of IBS in our study was similar to that of the French population, which suggests a limited selection bias in relation to digestive symptoms. Moreover, we proceeded to an extensive exclusion for self-reported organic disease and alarm symptoms and given the facilitated access to medical care in France, it is unlikely that a patient with gastrointestinal symptoms for several months would not be diagnosed for an organic disease. Generalization of our results to the general population is however subject to caution. Although we controlled for several confounding factors in relation to lifestyle and digestive tract symptoms, we cannot exclude residual confounding for the interpretation of our results. Finally, aORs represent a moderate increase of the risk of IBS.