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How Long Do FODMAPs Take to Trigger IBS Symptoms?

So you’ve just had breakfast and 30 minutes later you’re in the bathroom. You haven’t eaten anything since dinner last night, so it must have been breakfast, right?

Actually, you may be surprised, in the case of FODMAPs it is more likely to be what you ate for lunch or dinner yesterday that has sent you running to the bathroom.

What happens when we eat FODMAPs?

When we eat, food passes from the mouth down the esophagus to the stomach. In the stomach, food is mixed and broken down before being slowly released into the small intestine. Enzymes in the small intestine continue to break food down to single molecules so that it can be absorbed across the wall of the small intestine into the bloodstream. Any part of food that isn’t broken down or absorbed in the small intestine will continue its path down the digestive tract and pass into the colon for elimination.

There are two processes that can occur during this progression that may trigger symptoms of IBS, including bloating, cramping, wind, constipation or diarrhea or both:

  1. Certain FODMAPs are highly osmotic and readily draw water into the small and large bowel. This can affect how fast the bowel moves, and cause diarrhea.
  2. When FODMAPs reach the large bowel or colon, they are fermented by the bacteria that naturally live there and just like when beer is fermented, this process creates gas and bubbles, resulting in abdominal distention, bloating and cramping.

FODMAP reactions occur in the colon, at the very end of the digestive tract. From the beginning to end (the mouth to the anus) the average adult digestive tract is about 9 meters long. On average this means it takes about 6-24 hours from the time food is eaten until it reaches the colon where FODMAPs are fermented, resulting in IBS type symptoms.

Why do I get symptoms 30 minutes after eating?

This is known in medical terms as the “gastro-colic reflex”. At any point in time, most people have about 24 hours or more worth of food in their digestive system. The reason symptoms can occur soon after eating is that when we chew, the gastro-colic reflex is triggered. This reflex tells the gut that more food is coming and it needs to move things along and make room. This then pushes food, that is sitting in the small bowel from an earlier meal, into the colon triggering symptoms fairly soon after a meal.

How long do symptoms last?

How long symptoms last is variable, from a few hours to a day or so. Many people also find that after a gut upset, it can take a few days to a week to feel normal again.

Final Thoughts

Since reactions occur several hours after eating a problem food, it can be difficult to pinpoint triggers. If you are having trouble, a food and symptom diary and a trip to a FODMAP trained dietitian can help to identify patterns.

This article represents the opinions, thoughts, and experiences of the author; none of this content has been paid for by any advertiser. The team does not recommend or endorse any products or treatments discussed herein. Learn more about how we maintain editorial integrity here.


  • Maria1
    7 months ago

    how do you know which causes the reaction? whether its food from the day before or gastro-colic reflex?

  • Emily
    2 years ago

    So true that as soon as I finish eating I can go to the bathroom. I’ve felt a lot of my attacks were due just to the act of chewing.

  • jaeger91
    2 years ago

    This is very helpful. I had been wondering how this works and wasn’t familiar with the gastro-colic reflex. It totally explains one of the things I’ve been experiencing.

  • Poll