How quickly do FODMAP reactions occur?

Before starting a low FODMAP diet our flare-ups can seem random and unpredictable. Once we begin to learn about our triggers the timing of symptoms appears to make more sense. Despite this new understanding, many people are still surprised to learn how quickly FODMAP reactions occur.

It can take anywhere between 4-24 hours after eating for a reaction to begin. The answer to exactly how soon a reaction will occur can be different for each of us. The timing of FODMAP reactions are influenced to some degree by things such as;

• when you last ate
• which FODMAP type you’ve eaten
• the speed and motility of your digestion
• your age

However, the biggest factor in the timing of FODMAP symptoms is the physical structure of our digestive systems. [1]

Why FODMAP reactions take time

In the average adult, the length of the digestive tract from mouth to anus is roughly 8-9 metres long. FODMAP reactions take place in the large intestine/colon, towards the end of the digestive tract. Here they are rapidly fermented and this is what causes our FODMAP related symptoms. This means that it can take anywhere between 4-24 hours for the food you last ate to reach the colon and for the symptoms to begin to occur.

After your food reaches the colon it can take 2-3 more days before being fully eliminated from the body. This is the reason that a 3 day washout period is advised in between FODMAP challenges. [2]

At any one time, we each have at least one days worth of food moving through our digestive system. It’s important to remember this when we are trying to pinpoint which food may have caused our symptoms.

When we eat, our body’s natural response is to move food through our digestive system to make more room. This is known as the gastro-colic reflex [3] and is often what’s responsible for feeling as though the meal you just ate has gone ‘straight through you’. What’s actually happened is the meal you have just eaten stimulates the gastro-colic reflex and food from previous meals is moved through and out of the digestive system. This is why most people tend to go to the bathroom shortly after eating rather than at random times throughout the day.

My symptoms begin soon after eating

If your symptoms are occurring soon after eating then it’s likely that these are not FODMAP reactions. [4, 5] Some people may suffer from other conditions, in addition to their IBS which they may or may not be aware of. Explanations for these different digestive symptoms and their timings include:

• Food allergies
• Food intolerances such as lactose intolerance or histamine sensitivity
• Gastro-oesophageal reflux disease or GORD/GERD
• Exaggerated gastro-colic reflex
• Dumping syndrome
• SIBO
• Pancreatic enzyme insufficiency / Fat malabsorption issues
• Abnormal gut motility
• Visceral hypersensitivity

Your doctor and gastroenterologist should be able to identify other possible non-FODMAP factors that are contributing to your symptoms. Your dietitian will help you to make sense of the timing of your reactions and pinpoint the most likely causes.

Are you looking for more support during your reintroduction phase? Check out the other posts in this series.

How quickly do your FODMAP reactions occur? Let's compare in the comments below.