How do alcohol and coffee affect IBD?
Neither alcohol nor coffee has been shown to cause IBD, and the evidence that they trigger flares is weak. Even so, both can irritate the gut, and many people notice they make symptoms like diarrhoea or cramping worse, especially during a flare. Coffee tends to speed up the bowel, and alcohol can be a personal trigger. There is no blanket rule to cut them out: it comes down to how your own body reacts.
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This is a common worry at social occasions, so it is worth splitting into two questions: do they cause IBD, and do they make symptoms worse?
What the evidence says about cause
Neither drink has been shown to cause the disease. The Crohn's & Colitis Foundation states there is no clear evidence that coffee or alcohol consumption is causally linked to developing Crohn's disease or ulcerative colitis (Crohn's & Colitis Foundation). So enjoying a coffee or a drink did not give you IBD, and is not keeping it going.
How they can affect symptoms
Symptoms are a different matter. Crohn's & Colitis UK notes there is not enough high-quality evidence to be certain whether alcohol raises the risk of a flare, but many people report that it makes their symptoms worse (Crohn's & Colitis UK). Caffeine appears on the same page among the things that can make diarrhoea worse, which fits the way coffee tends to speed up the bowel (Crohn's & Colitis UK).
It comes down to you
Because the effect is so individual, there is no blanket order to give everything up. Many people are fine in remission and more careful during a flare. Noticing your own pattern, perhaps with a short food diary, tells you more than any general rule.