By Dr Jane Varney (Research Dietitian)
Caffeine (usually in the form of coffee) is commonly implicated as a trigger of IBS symptoms. But does caffeine really play a role in triggering IBS symptoms and should you adjust your intake?
Studies that have investigated the proportion of people with IBS who implicate coffee with the onset of symptoms reveal that 26-40% identify coffee as a symptom trigger[1, 2]. Other studies have shown that up to one third of people with IBS experience a recurrence of symptoms (commonly diarrhoea) with the open reintroduction of caffeine (following symptom improvement on an elimination diet)[3-6]. While these findings are interesting, they are derived almost exclusively from observational studies, so cause and effect relationships (between caffeine intake and symptom inset) cannot be drawn. The studies also used ‘open challenges’ and thus failed to exclude the powerful placebo effect – that is, the response triggered by expectation, not by the treatment per se.
Assuming that caffeine plays a role in triggering IBS symptoms in some individuals, how might this occur? The effect of caffeine on gastrointestinal symptoms may be related to its effects on colonic motor activity. This was shown in a study which showed that coffee induced the need to defecate (poo) in nearly one third of healthy participants. These effects were observed after coffee, but not water. Another small study in healthy participants showed that coffee may increase gastrointestinal motility to a similar extent as a meal, and a greater extent than water and decaffeinated coffee. Gastrointestinal motility refers to movements of the digestive system and the transit of the contents within it.
So should you change your caffeine intake to improve your IBS symptoms? Given the lack high quality evidence in this area, blanket recommendations about caffeine intake are certainly not warranted. Instead, work with your dietitian to determine whether your symptoms are related to your caffeine intake. If there appears to be a link, make sure that any change in your caffeine intake (up or down) is made in isolation so that any effects can be monitored and detected.
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