In our study population, we observed that drinking patterns did not differ significantly between women with and without IBS. Among women with IBS, 80% reported consuming alcohol on at least one occasion. Prior studies have reported that approximately 12-17% of adults with IBS reported perceived intolerances to alcohol.6,7
In contrast, another study observed that 48% of IBS patients abstained from drinking alcohol (based on a questionnaire asking about past alcohol consumption) ; however, this higher percentage may be due to differences in definitions of alcohol intake with the latter study defining abstention as drinking less than 12 drinks per year, as well as their retrospective ascertainment of alcohol consumption.12
We observed that binge drinking was associated with GI symptoms among women with IBS, but that moderate to light drinking was not associated with GI symptoms to any appreciable degree. Our interpretation of these results is complicated by our finding that associations of alcohol consumption and GI symptoms were strongest when comparing between persons. Taken together, this would indicate that IBS patients who binge drink experience greater GI symptoms in general as indicated by the higher mean level of GI symptoms among women who reported binge drinking; however, our data also suggest that an individual's symptoms don't necessarily correlate with specific episodes of binge drinking. Thus, it may be that individuals who binge drink experience chronic changes in their gut that are associated with increases in GI symptoms. In addition, this association persisted after controlling for an individual's stress, indicating that the influence of alcohol on gut symptoms was not confounded by a person's emotional state. In further analysis, we report that the associations between alcohol intake and GI symptoms were strongest among the IBS-D group. We did not observe evidence of a role of alcohol intake on GI symptoms for women with IBS-C within our study population. Nor did we observe an association between pattern of alcohol use and GI symptoms among control women.
In the literature, it has thus far been unclear whether alcohol intake affects GI symptoms in IBS patients.1
Several reasons may exist for the lack of consistency in the published research. First, there are many study designs employed to investigate alcohol and IBS. The prior studies that have reported a link between alcohol and IBS have primarily focused on IBS patients’ perceptions of alcohol's impact on GI symptoms.6,7
On the other hand, asking participants to report past alcohol consumption (for example in case-control studies) may not be sensitive enough to examine associations between alcohol and GI symptoms in IBS patients.3-5,12
Secondly, investigating patterns of alcohol use may be required to elucidate the role of alcohol intake in GI symptoms. In two prior studies where adults were asked about weekly patterns of drinking using questionnaires asking about typical, past alcohol consumption, researchers reported no association between patterns of alcohol intake and IBS.5,12
However, to the extent that amount of alcohol consumed matters in IBS symptoms, detailed prospective assessment of daily alcohol consumption may be required.
Alcohol and its metabolites are known to affect the GI tract motility, absorption, and permeability. Alcohol decreases gastric motility in mice.13
In the small intestine, alcohol decreases the impedance wave motility (muscles that retain food for further digestion) but does not affect the propulsive wave motility (movements that propel food within the intestine) contributing to diarrhea seen in individuals who chronically consume alcohol.14,15
Alcohol has also been shown to increase intestinal permeability in both animals and humans.14,16
By measuring urine sugars, increased intestinal permeability in both the small intestine and colon has been found in patients with IBS.17
Chronic alcohol users demonstrate malabsorption of carbohydrates, fat, proteins, and xylose compared with non-alcohol abusers.14,15,18
These effects either individually or combined can worsen IBS symptoms. For example as alcohol decreases motility and absorption of carbohydrates, stasis can increase the effects of carbohydrates such as fermentable carbohydrates (FODMAPs) that can result in IBS symptoms, including abdominal pain.19,20
In addition, alcohol is also noted to have gut mucosal injury in animals21
and in chronic alcohol abusers.22
Furthermore, chronic alcohol exposure alters the microbiota reducing its variability (i.e., microbial richness),23
and this change has been found to correlate with elevated serum endotoxin levels.24
These chronic changes in response to alcohol could in part explain the greater differences we observed between persons than within a person.
Our study observed that diarrhea, stomach pain, and indigestion were strongly associated with binge drinking. Furthermore, our study reports that associations between alcohol intake and GI symptoms were strongest among the IBS-D group. Of the studies reporting on GI symptoms, several found alcohol to be associated with various GI symptoms,5,6
but not all.12
Specifically, 8% of people with IBS reported alcohol intake to be associated with loose stool/urgency.6
Another study reported that high alcohol intake, but not moderate intake, was associated with abdominal pain. These findings are in broad agreement with our study's findings regarding GI symptoms. Moreover, our study's findings are in agreement with the literature detailing the physiologic effects of alcohol on the gut. In particular, gut mucosal injury could explain the increased abdominal pain, nausea, and indigestion.
With respect to caffeine and cigarettes, both have been demonstrated to affect gut motility in normal individuals.1,25
However, their roles in IBS patients are less clear.1,26
Prior studies have reported that coffee drinking is not more common among IBS patients, but a role of caffeine in IBS symptoms is supported by studies demonstrating that reintroduction of coffee led to the return of IBS symptoms in up to a third of IBS patients.1
For cigarette smoking, results from one study indicated that half of IBS patients with predominant constipation who smoked cigarettes reported that cigarette smoking led to softer stools.26
However, any other evidence linking smoking to GI symptoms in IBS patients is lacking. With the exception of cigarettes and symptoms of constipation, our data suggest that caffeine and cigarettes play at most a modest role in GI symptoms among women with IBS.
The primary limitations of this study are as follows. First, our daily diaries do not provide a temporal sequence between alcohol, caffeine, cigarettes and GI symptoms within the day. However, we attempted to overcome this issue by investigating the role of lifestyle factors on next day's GI symptoms. Because symptoms related to alcohol are often observed the following day, this approach works well for investigations regarding alcohol. However, this approach may not be appropriate for cigarette smoking and caffeine because their effects on the gut may be of a shorter timeframe; thus, our analysis did not adequately address the temporal sequence between GI symptoms and smoking and caffeine intake. In addition, while the study participants were taught how to complete the alcohol section of the daily diary according to wine, beer, and liquor consumption, no information was collected on the type of alcohol within the daily diary. Overall, a primary strength of our study is our prospective data on daily cigarette, alcohol and caffeine intake, as well as prospective ascertainment of GI symptoms.
In summary, we observed alcohol consumption among IBS patients to be associated with GI symptoms, but this was primarily limited to those who consumed high amounts of alcohol and to women with IBS-D. Our data suggest that IBS patients, particularly women with IBS-D, who binge drink may experience an increase in GI symptoms that are not limited to their episodes of binge drinking. While our findings would require replication before conclusions are to be drawn, these findings provide early indications that the pattern of alcohol intake (i.e. binge drinking) predominantly influences GI symptoms of women with IBS.