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How Long Should I Stay on the FODMAP Elimination Phase?

How long should you stay on the elimination phase of a FODMAP elimination diet? This is an important question; you will read and hear a wide variety of opinions on the subject. Some of that advice is just plain bad. FODMAPs are not evil. Most FODMAP-containing foods are not "bad foods." Beware of dodgy advice you might read that suggests you should stay on the elimination phase of the diet as long as possible. The best advice comes directly from the doctor or dietitian who knows you best. My short answer is: don't stay on it any longer than you have to.

Many high-FODMAP foods contain valuable nutrients and taste great! How long should you wait before reintroducing them?

Many high-FODMAP foods contain valuable nutrients and taste great! How long should you wait before reintroducing them?

  • An elimination diet is a learning diet, not a permanently restricted diet.
  • The time period should be long enough for it to be apparent whether or not the low FODMAP approach will help the individual person.
  • As it is, even during the challenge process you will be continuing to eat the baseline elimination diet, so it does last longer than it might seem at first.
  • In order to get a balanced diet with a variety of nutrients from food, it is important to liberalize the diet as tolerated, using either food challenges as described in IBS--Free at Last! or a more cautious approach, gradually liberalizing diet as tolerated.
  • Let's face it, lots of people have a limited attention span for dietary change. If we stretch the process out too long, we may lose focus, and could leave valuable information about how food affects us on the table.
  • Several of the earlier clinical studies on low FODMAP diets were conducted with longish elimination phases of 6-8 weeks. However, a 2014 Monash University study by Emma Halmos and colleagues demonstrated that the greatest change in GI symptoms for a group of IBS patients occurred in the first seven days of the low-FODMAP study diet and was maintained thereafter. That is consistent with what I've seen in my practice over many years of working with IBS patients.
  • The osmotic effects of FODMAPs (pulling fluid into the gut, causing pain, urgency and loose stools) literally cannot take place after they have passed out of your body. "They must be present to win." So, for example, if a lactose intolerant person eats ice cream on Sunday night, has a bout or two of watery diarrhea on Monday and passes all the lactose remnants by Monday night, that lactose is gone. It cannot still be causing osmotic effects on Thursday, or 6 to 8 weeks later, for that matter.
  • On the other hand, it is possible that people who tend toward constipation and have very slow transit times might still have some FODMAPs on board for a longer time period until their gut bacteria consume it. These may be people for whom the fermentability of FODMAPs is a bigger problem than the osmotic activity. At first it would seem that once the excess gas produced by fermentation has been passed, this effect of FODMAPs would also cease, and I have worked with many constipated patients who did feel much better within a day or two. However, because FODMAPs feed and change the gut microbiome, improvements could continue to build up over time for some people, as the biomass evolves. Every now and then someone reports that they did not reap the full benefit of the diet for five or six weeks.
  • If you've been on the diet for longer than that and you just aren't feeling better, staying on it longer, sadly, is not going to help. Time to try something else.
  • If you are feeling better after several weeks, its time to move on, using either food challenges or the more cautious approach described in IBS--Free at Last!
  • If you are working with a dietitian, he or she may be using FODMAPs in a slightly different way, with different timelines tailored to your personal medical situation. That's a good thing!

Bottom line, two to three weeks is plenty of time in most cases for people to get organized, try the diet, and know if the FODMAP approach is helping. Re-read IBS--Free at Last! for help planning the challenge phase, and please consult a registered dietitian if you need individualized advice.

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