Low-FODMAP Protocol — Body Handbook

Gut · §78

Low-FODMAP Protocol

If you have IBS, low-FODMAP is the closest thing diet has to a real answer: about two in three people see bloating, pain, and unpredictable bathroom trips drop within a month Halmos et al. 2014. Here's what you didn't know you didn't know: it isn't a diet, it's a three-phase diagnostic course with an end date. Cut the suspects, reintroduce them to find your own triggers, then eat everything else freely. Done right, it ends with a calmer gut and a wider plate.

Do · Course Evidence Moderate Chapter Gut

FODMAPs are a family of carbs your small intestine can't fully absorb. The fructans in wheat, onion, and garlic; lactose; excess fructose in apples and honey; the sugars in beans; polyols in stone fruit and sugar-free gum. They pull water in and ferment into gas. In a normal gut you feel nothing; an IBS gut wall is hypersensitive to the stretch, so the same gas becomes pain ¹.

The diet doesn't treat IBS — it removes one big set of triggers. That's why a third of people don't respond: their trigger is something else. For those who do, it ranks first for pain and bloating against standard eating advice ², and it's the formal second-line move once basic advice fails ³.

Phase 1, Elimination (2–6 weeks). Cut all five FODMAP groups at once. Check every serving in the Monash FODMAP app — a blog list from two years ago is out of date. Eat low-FODMAP versions of normal food: rice, oats, eggs, chicken, hard cheese, lactose-free milk. No change by week four at real adherence means you're a non-responder; move on anyway.
Phase 2, Reintroduction (6–8 weeks). Keep the low-FODMAP background. Test one group at a time with a "test food" for three days, small to large, then wait two to three days and log it. Milk tests lactose, mango fructose, wheat bread fructans, chickpeas the bean sugars.
Phase 3, Personalisation (long-term). Put back everything you tolerated; manage portions on the rest, since tolerance is a serving size rather than on/off. Re-test the triggers every three to six months.
Get a trained dietitian. Over-restricting in phase 1 and misreading your own triggers are what they prevent ⁴; in the US most insurance covers the referral.

Most people finish tolerating two or three groups freely and watching portions on the rest. That's the destination, not lifelong elimination ⁵. The Monash app runs about ten dollars, once.

What the phases buy you. Responders notice the belly staying flat through the afternoon within two weeks; by week four the bathroom trips land where you expect. Phase 2 is the part that pays for the year: you finish knowing by experiment that lactose is fine and onion isn't. Phase 3 restriction is small — order the burger without the aioli, take a Lactaid before the latte. In a three-to-four-year cohort, six in ten who finished still had adequate relief ⁵, and the fibre lost in phase 1 comes back ⁶.

The fine print — when to skip it, and what people get wrong

It's not gluten-free: wheat is cut for its fructans, not gluten, so sourdough spelt and gluten-free pasta are fine. FODMAPs aren't bad for you either — they feed healthy colon bacteria, and people without IBS shouldn't do this.

Stopping at phase 1 is the dominant failure: about half never finish reintroduction, trading the course for years of needless restriction ⁴. Old internet lists are second — they miss hidden sources like inulin in protein bars.

References

1Halmos EP, Christophersen CT, Bird AR, Shepherd SJ, Gibson PR, Muir JG (2015). Diets that differ in their FODMAP content alter the colonic luminal microenvironment. Gut. link
2Black CJ, Staudacher HM, Ford AC (2022). Efficacy of a low FODMAP diet in irritable bowel syndrome: systematic review and network meta-analysis. Gut. link
3Lacy BE, Pimentel M, Brenner DM et al. (2021). ACG clinical guideline: management of irritable bowel syndrome. American Journal of Gastroenterology. link
4Whelan K, Martin LD, Staudacher HM, Lomer MCE (2018). The low FODMAP diet in the management of irritable bowel syndrome: an evidence-based review of FODMAP restriction, reintroduction and personalisation in clinical practice. Journal of Human Nutrition and Dietetics. link
5O'Keeffe M, Jansen C, Martin L et al. (2018). Long-term impact of the low-FODMAP diet on gastrointestinal symptoms, dietary intake, patient acceptability, and healthcare utilization in irritable bowel syndrome. Neurogastroenterology & Motility. link
6Harvie RM, Chisholm AW, Bisanz JE et al. (2017). Long-term irritable bowel syndrome symptom control with reintroduction of selected FODMAPs. World Journal of Gastroenterology. link

Related in the handbook (6)

Helps

— Bloating is one of the symptoms that drops fastest in phase one for the people this works for.
— This is the best-tested diet we have for IBS — two in three people get real relief if they finish all three phases.

— The low-FODMAP protocol is the gold-standard version of this: strip, reintroduce, then settle on what you can actually eat.
— If a clean low-FODMAP run only half-helped, dietary histamine may be the other driver behind the bloating and headaches.
— In blinded testing, FODMAPs — not gluten — trigger most people's symptoms; the low-FODMAP approach often beats going gluten-free.
— Resistant starch is fermentable, so it can overlap with the FODMAPs that trigger IBS — go slow if your gut is sensitive.