SIBO Diet vs Low FODMAP: What the Evidence Says

If you have been told you have small intestinal bacterial overgrowth (SIBO), you have probably met two competing food lists: the low FODMAP diet, and something sold as "the SIBO diet", most often the low fermentation diet. Here is the honest comparison. Low FODMAP is the only one of them with randomised trials behind it, and those trials were done in irritable bowel syndrome (IBS), not SIBO. The low fermentation diet and the other SIBO food lists have no published trial that we could find. No ordinary diet has been shown to clear overgrowth. The one dietary approach studied specifically for its effect on the breath test is an exclusive elemental formula, in small studies with no control group.

That last point matters because it reframes the whole choice. You are not choosing between a treatment and a non-treatment. You are choosing between two ways of reducing symptoms while something else, usually an antibiotic or time, deals with the overgrowth. This article sets the two food lists side by side, shows exactly where they disagree and why, reads the small number of SIBO-specific diet studies closely (including two with numbers that do not add up), follows the money behind the low fermentation brand, and answers the questions people actually ask on r/SIBO: why the breath-test prep diet felt so good, whether to eat normally during antibiotics, and how to stop losing weight.

A note on method: when we say "we found no trial", that reflects our searches of PubMed, Europe PMC and the guidelines cited here, not proof that none exists anywhere.

The short answer: one diet has trials, the others have food lists

The low FODMAP diet has a real evidence base, but almost all of it comes from people with IBS. Pooling 13 randomised trials and 944 patients, a low FODMAP diet ranked first against habitual diet for global IBS symptoms, with a relative risk of symptoms not improving of 0.67 (Black 2022). The authors added that most trials were in specialist care and did not study the reintroduction phase.

For SIBO specifically, a 2022 narrative review that set out to answer exactly this question concluded that, on the available literature, the potential efficacy of the IBS diet in SIBO is "largely hypothetical", and that a low FODMAP diet might deepen the dysbiosis it is meant to calm (Wielgosz-Grochowska 2022).

The SIBO-branded diets are in a weaker position still. We could not find a published trial of the low fermentation diet or of the other practitioner-designed SIBO food lists. The only "SIBO diet" studied specifically for its effect on overgrowth is the elemental diet, which is not food at all but an exclusive liquid formula (Pimentel 2004, Rezaie 2025).

If you came here because you are still deciding whether your symptoms are SIBO or IBS in the first place, that question has its own article: SIBO vs IBS symptoms covers what the breath test does and does not show. This post assumes you already have a result and want to know what to eat.

What each "SIBO diet" actually is

The word "SIBO diet" covers several different things, and they make very different claims. Here is what each one is and what we could find tested.

The low fermentation diet is the one most often set against low FODMAP, and its own published food list shows how different the logic is. It avoids apples, bananas, pears, broccoli, cabbage, cauliflower, bok choy, oatmeal, brown rice, whole wheat bread, lentils and beans, tofu, chia and flax, psyllium, lactose-free yoghurt "due to the live cultures", stevia and sucralose. It allows white or wheat bread, rye bread, sourdough, couscous, mango, cherries, peaches, mushrooms, leek, small amounts of onion, cooked garlic, honey in small amounts, beer and wine. It also advises limiting carbohydrates to one serving per meal (Good LFE).

That is not a stricter version of low FODMAP. It is a different diet, with substantial overlap and several direct contradictions.

The Specific Carbohydrate Diet is the only SIBO-adjacent diet we found compared head to head with low FODMAP, and the trial was in IBS, not SIBO. In 73 people randomised for three months, the low FODMAP group improved significantly on bloating and distension while the SCD group showed only a trend. Mean vitamin D fell from 38 to 32 ng/mL on low FODMAP and to 22 ng/mL on SCD, and folate fell further on SCD as well (Vincenzi 2017). The paper has reporting oddities worth knowing: its abstract mentions a difference "after 12 days" in a three-month trial, and reports folate in units that look wrong for blood folate. We could not resolve either from the abstract, so treat the numbers as indicative.

Where the two food lists disagree, and why

The disagreements are not random. They follow from two different theories of where the problem is happening.

Low FODMAP is a colon-and-small-bowel diet built on measured food chemistry. FODMAPs are short-chain carbohydrates that are poorly absorbed, so they deliver extra water and rapidly fermentable material to the distal small intestine and proximal colon (Gibson 2010). The list is built from laboratory measurements. Garlic, artichoke, shallots, leek and onion carry the highest fructan loads of 60 vegetables measured (Muir 2007). Among cereal grain products, fructan per portion ranged from 1.12 g in couscous to none in rice (Biesiekierski 2011). Certain fruits carry sorbitol and certain vegetables carry mannitol (Yao 2014).

The low fermentation diet is a small-bowel diet built on a theory of absorption speed. Its food list explains that table sugar "is absorbed higher up in the GI tract before the bacteria can feed off of it" (Good LFE). The idea is that refined starch and simple sugars are absorbed early, before they reach bacteria further down, while fibre, whole grains and legumes travel on and get fermented. A 2025 review describes the same rationale for meal spacing and phase III motor activity (Velasco-Aburto 2025).

There is a real physiological point underneath that. The European breath-testing guideline notes that the term FODMAP was defined by chemistry rather than by biological effect, and that it does not include incompletely absorbed starches and many dietary fibres that also reach the large bowel unchanged (Hammer 2022). So a low FODMAP diet can still contain plenty of fermentable material, such as oats, brown rice, firm tofu and certain vegetables. The low fermentation diet removes more of that, and allows back some fructan-containing refined foods that are low in fibre.

What nobody has done is test whether either theory predicts symptoms or breath test results better in people with SIBO. The table below sets out the main conflicts and what evidence sits behind each side.

If you have been reading r/SIBO, you will recognise the effect this has on people. In a 59-comment thread asking whether anyone had found the low fermentation diet helpful, the original poster struggled to see how a SIBO diet could permit onions, garlic and white bread. Replies split almost evenly: some described it as the most livable approach they had tried, others reacted badly to its starches or its fruit, and one person working with a dietitian described using it as a blueprint and still having to drop foods it allows (r/SIBO). In a much shorter thread, one reply put the opposite view bluntly: low FODMAP is the better researched diet and the low fermentation list contains foods that send them running (r/SIBO). Both are honest descriptions of individual responses. Neither is evidence about which diet works better, because that comparison has not been run.

What gas measurements show about low FODMAP

The strongest mechanistic evidence for low FODMAP comes from breath testing, which is also how SIBO is diagnosed. In a single-blind crossover study, 15 people with IBS and 15 healthy volunteers ate diets that differed only in FODMAP content, about 9 g a day versus 50 g a day, for two days each. Breath hydrogen across the day was roughly four times higher on the high FODMAP diet in both groups: in IBS, 242 versus 62 units over 14 hours. Methane was different: it fell on the high FODMAP diet in healthy volunteers but did not change in people with IBS (Ong 2010).

Two things follow. First, cutting FODMAPs reliably cuts hydrogen production, which is plausibly why many people with a hydrogen-positive breath test feel better on the diet. Second, methane did not respond in the same way in IBS, which fits the common r/SIBO experience that methane-dominant overgrowth (now often called intestinal methanogen overgrowth, or IMO) is harder to move with diet. That second point comes from one small study, so treat it as a hint rather than a rule.

Lower gas production is not the same as fewer bacteria. The diet changes what the bacteria are fed. It has not been shown to change how many of them live in the small intestine.

What the SIBO-specific low FODMAP studies actually show

There are three places SIBO-specific low FODMAP data exist, and each needs reading closely.

An online survey from a hospital clinic in Bialystok, 2026. This is the largest SIBO-specific low FODMAP study we found. It surveyed 98 patients who had previously followed the diet, using an original, unvalidated online questionnaire. Of respondents, 82.7% had been diagnosed with SIBO, 51% with IMO and 37.8% with IBS, and patients could tick more than one. Most (90.8%) had taken antibiotics before starting the diet. Bloating fell from 8.31 to 3.28 on a 0 to 10 scale, and the authors concluded the benefit was independent of the initial diagnosis (Bogdanowska-Charkiewicz 2026). The paper discloses that one author founded a clinic named Klinika MajDiet, and reports no external funding.

The study does contain a useful finding for anyone weighing up the reintroduction phase: people who completed both elimination and reintroduction had about 3.4 times the odds of being a responder (OR 3.43). Taking antibiotics before the diet was associated with a much higher odds of response (OR 7.10), but since 90.8% of the sample had done so, that comparison rests on a small group, and its confidence interval runs from 1.28 to 44.64.

A randomised trial of rifaximin versus low FODMAP in IBS, 2026. In 100 adults with IBS, composite response at four weeks was 56% on rifaximin and 48% on low FODMAP, not a significant difference. Rifaximin worked faster for bloating and pain, and adherence was better (95.9% versus 77.8%). Only 17% of participants had SIBO, and among them eradication was 63.6% with rifaximin and 50.0% with the diet (Chuah 2026). That is roughly 17 people split across two arms, so those eradication figures cannot tell you much. The trial was funded by an institutional research grant.

A randomised trial of add-on supplements, 2024. In 179 people with SIBO, both arms received antibiotics and a low FODMAP diet; the intervention arm also got herbal antimicrobials, probiotics and prebiotics (Redondo-Cuevas 2024). It is worth knowing about only because it shows how the diet is usually treated in SIBO research: as background, not as the thing being tested.

So when a page tells you low FODMAP "treats SIBO", the evidence underneath is a retrospective survey with a mislabelled headline, a handful of people in the diet arm of an IBS trial, and trials where the diet was never the variable.

Does any diet clear SIBO, or just quiet it?

For ordinary food, the answer is: quiet it. The AGA's patient guidance, reviewed in 2026, puts it plainly: "Changing your diet can help reduce symptoms of SIBO, but diet alone is not able to cure SIBO." It describes the evidence for low FODMAP as coming mostly from IBS and calls it "a way to ease symptoms rather than a proven treatment for overgrowth itself" (AGA patient guidance).

The AGA's clinical practice update for doctors says management should focus on identifying and correcting underlying causes, correcting nutritional deficiencies, and antibiotics. That headline management statement does not name a diet (Quigley 2020).

The nearest thing to a test is the IBS trial above, where half of the few participants with SIBO in the diet arm had a negative repeat breath test after four weeks. With so few people and no untreated group for comparison, that cannot tell you whether the diet, time or chance explains it (Chuah 2026).

This is worth holding onto when a diet does not seem to be "working". If you feel better on it, it is doing its job. If your next breath test is still positive, the diet has not failed, because clearing overgrowth was never something it was shown to do.

The elemental diet: the one diet studied for clearance

The elemental diet replaces all food with a formula of pre-digested nutrients, typically free amino acids, simple sugars and fats, for around two weeks. The theory is that it is absorbed so early in the small intestine that bacteria further down are starved.

The 2004 study. People with IBS and an abnormal lactulose breath test drank an exclusive elemental formula for two weeks. Of the 93 available for analysis, 74 (80%) had a normal breath test on day 15, and five more normalised after an extra week (85%). On a chart review a month later, those whose test normalised reported a 66.4% improvement in bowel symptoms, compared with 11.9% in those whose test did not (Pimentel 2004).

There is a discrepancy we cannot settle. The abstract reports 93 subjects available for analysis. A 2025 review describes the same study as involving 124 patients with 11% dropping out because they could not tolerate the diet (Velasco-Aburto 2025). Eleven percent of 124 is about 14 people, but 124 minus 93 is 31. Both could be true if some people were lost for other reasons, but neither source we could read explains the gap, and we could not access the full 2004 paper.

The 2025 trial. Thirty adults with SIBO, IMO or both took an exclusive "palatable" elemental formula for two weeks, then reintroduced food. All 30 completed it. Breath tests normalised in 22 (73.3%), and 83% reported adequate global relief of symptoms. By group, normalisation was 100% in the 6 people with hydrogen SIBO only, 58% in the 12 with IMO, and 75% in the 12 with both (Rezaie 2025). There was no control group, and follow-up after stopping the diet was two weeks. The authors acknowledge both.

People lost weight, too. Average weight fell from 70.4 kg to 67.0 kg over the two weeks of formula, even though the diet was matched to each person's calorie needs, and it was 67.7 kg two weeks after food came back (Rezaie 2025).

The r/SIBO experience is mixed in a way the trial cannot capture. One widely read account described doing three weeks on a semi-elemental product, feeling worse from about day 16, and a repeat breath test showing methane nearly doubled; the poster suspected added sugars in some versions of the formula and later settled on a looser lower FODMAP pattern with meal spacing (r/SIBO). That is one person, with no way to know why their result moved. It is a reminder that "elemental", "semi-elemental" and a specific trial formula are not interchangeable, and that this is a medical intervention to plan with a doctor, not a diet to start alone.

Follow the funding

The low fermentation diet and the 2025 elemental formula trace back to the same group, and the paper's disclosures say so.

None of that means the findings are wrong. It means the people who designed the diet, ran the trial and sell the product overlap, which is exactly the situation in which independent replication matters most.

The vendor's own numbers also do not match the paper. The mBIOTA evidence page headlines "100% of patients eradicated SIBO", states that "83% of patients normalized their lactulose breath test after 14-day elemental diet" citing the 2025 trial, and that "63% of IMO patients eradicated methane overgrowth". Lower on the same page it says the formula "eradicated overgrowth in 73% of patients overall" (mBIOTA). The published paper reports 73.3% normalisation overall, 100% in the six people with hydrogen SIBO only, and 58% in the IMO-only group; 83% is the paper's figure for symptom relief, not breath test normalisation (Rezaie 2025). A plausible benign reading is that the page mixes figures from different subgroups or earlier conference abstracts. Without the source for the 83% and 63% figures, we cannot reconcile them, and the 100% figure describes six people.

Why your bloating vanished on the breath-test prep diet

This is one of the most common surprises on r/SIBO. In one thread, someone two days into breath-test preparation on eggs, plain white bread, white rice, chicken and black coffee found their gas, cramps and bloating gone and their stomach flat, after weeks of low FODMAP that had not helped (r/SIBO).

That is the prep diet doing exactly what it was designed to do. The North American breath testing consensus suggests avoiding fermentable foods such as complex carbohydrates on the day before testing, notes that meat and rice do not appear to affect the result, and explains that the point is to get a low fasting hydrogen level (Rezaie 2017). The European guideline recommends avoiding poorly absorbed fermentable carbohydrates and dietary fibre for at least a day beforehand, and notes that a low fibre or low FODMAP diet decreases breath hydrogen (Hammer 2022).

The gap between the prep diet and low FODMAP is real and worth using. A low FODMAP diet still contains fibre and starch, so if one felt dramatically better than the other, that is information for your dietitian about which fermentable components you react to. Replies in that thread raised other possibilities too, including FODMAP stacking on the low FODMAP diet, which our guide to FODMAP stacking examples explains, and a slow-emptying stomach, which only a clinician can assess.

The British Society of Gastroenterology recommends against hydrogen breath testing for SIBO in people with typical IBS symptoms, partly because these tests can be falsely positive in IBS due to rapid transit (Vasant 2021). That is another reason to be careful about reading too much into how your gut feels on a test-prep diet.

Should you eat normally or restrict during antibiotics?

There is a recurring argument on r/SIBO. One camp restricts hard during antibiotics to "starve" the bacteria. The other eats normally or adds some fermentable foods on the theory that bacteria which are not feeding may respond less to the drug. In one thread, a person about to start treatment asked which to do; replies included eating everything, eating moderate FODMAPs, and avoiding long-term low FODMAP altogether (r/SIBO).

We found no trial that tested diet during antibiotic treatment for SIBO. The closest evidence points, awkwardly, away from strict starvation. In a randomised trial of 77 people with SIBO and a predisposing condition, adding partially hydrolysed guar gum, a soluble fibre supplement, to a 10-day rifaximin course raised eradication on a repeat glucose breath test from 62.1% to 87.1% per protocol (85.0% by intention to treat) (Furnari 2010). The authors' rationale was that the fibre affects intestinal motility. It is one small trial from a single centre, and symptom improvement among people whose test cleared was similar in both groups.

This is a question to put to whoever prescribes your treatment, because they may have a protocol in mind. Do not add a supplement or change how you eat during treatment without checking with them.

Meal spacing and the "cleaning wave"

Both the low fermentation approach and the AGA patient guidance recommend spacing meals. The reasoning is physiological. The migrating motor complex is a cyclic pattern of contractions in the stomach and small bowel that happens during fasting and is interrupted by eating. Its absence has been associated with SIBO, among other conditions (Deloose 2012).

The advice is plausible. It is also untested as a SIBO intervention, and the sources disagree on the number. The AGA patient page says it is ideal to wait at least three hours between meals or snacks and not to eat too close to bedtime (AGA patient guidance). A 2025 review describes low fermentation eating as using at least five hours between meals (Velasco-Aburto 2025). We found no trial comparing either interval, or comparing spacing with grazing, in people with SIBO.

Spacing also has a cost if you are struggling to eat enough, which is where the next problem comes in.

After treatment: which diet, and for how long?

This is the question most people actually have, and the honest answer is that nobody has tested it. The 2025 nutrition review states that dietary changes to maintain remission in SIBO "have not been rigorously studied", and that a low fermentation diet "theoretically" could reduce recurrence (Velasco-Aburto 2025). Theoretically is the operative word.

One r/SIBO commenter, citing a podcast, said the low fermentation diet's designer has never claimed it beats low FODMAP and created it as something patients could live with long term (r/SIBO). We could not verify that from a primary source, so take it as one person's account.

If you use low FODMAP after treatment, use it the way it was designed: a short elimination phase, then structured reintroduction, then a personalised long-term diet. The European breath testing guideline makes a related point for carbohydrate intolerance generally: a positive and lasting response to diet can confirm an intolerance, and the aim is to avoid unnecessary restriction (Hammer 2022). Our guide to how long to do the low FODMAP diet covers the clock, and how to reintroduce foods after low FODMAP covers the method. The one SIBO-specific signal we have points the same way: in the Bialystok survey, people who completed both phases did better than those who did not (Bogdanowska-Charkiewicz 2026).

If you want to see what a reintroduction schedule looks like in dates before you talk it through with a dietitian, our free planner lays one out.

If you use the low fermentation list instead, the same principle applies: it is a starting point to be personalised, not a permanent rule. People in the threads described adding back foods over time and finding that some foods it permits, such as certain fruits or starches, did not suit them.

The long-term cost: your microbiome and your nutrients

The worry that low FODMAP harms the microbiome comes up in almost every r/SIBO thread on this subject, and it has a basis.

In a randomised trial in IBS, four weeks of fermentable carbohydrate restriction reduced the concentration and proportion of bifidobacteria in stool, while 68% of the diet group reported adequate symptom control against 23% of controls (Staudacher 2012). In a crossover trial comparing a low FODMAP diet with a typical Australian diet for three weeks each, the low FODMAP diet reduced total bacterial abundance, while the higher FODMAP diet increased butyrate-producing bacteria and Akkermansia muciniphila. The authors wrote that the implications of long-term reduction "require elucidation" (Halmos 2015).

So the changes are real, and their long-term meaning is unknown. The low fermentation diet has not been studied for its microbiome effects at all, but it removes whole grains, legumes and several prebiotic-rich foods, so there is no reason to assume it is gentler.

The reassuring evidence comes from what happens after reintroduction. In a dietitian-led follow-up of 103 people with IBS, satisfactory symptom relief was 12% at baseline, 61% after restriction, and 57% at long-term follow-up after reintroduction. Most (82%) settled on an adapted diet with some FODMAPs back in, and nutritional adequacy was not compromised in either group (O'Keeffe 2018). That is IBS data again, but it shows the endpoint the diet is designed to reach: a broader diet, not a permanent elimination.

If you have noticed food fear building, or a long list of foods you no longer trust, our article on whether the low FODMAP diet can cause an eating disorder covers the warning signs and safer approaches.

Losing weight on a SIBO diet

Weight loss is a common and under-discussed problem. One r/FODMAPS thread came from someone with hydrogen SIBO who kept losing weight from an already low starting point on low FODMAP with four-hour meal spacing, despite eating large meals. Replies suggested adding fats, more of the foods they already tolerated, and in one case moving away from strict low FODMAP to a less restrictive approach (r/FODMAPS).

There are three overlapping reasons weight can fall. SIBO itself can interfere with absorption; the AGA's practice update lists nutritional deficiencies among its laboratory findings (Quigley 2020), and the AGA patient page warns of weight loss and deficiencies in vitamin B12 and vitamins A, D and E (AGA patient guidance). Restrictive diets make it harder to eat enough. And meal spacing removes the snacks that some people rely on.

What to do about it is individual, which is why it belongs with a dietitian. But some principles are safe. Unintended weight loss is a reason to tell your doctor promptly, not something to manage alone. Restriction should be as short and as loose as your symptoms allow. And if a diet is costing you weight without clearly helping, that is a reason to stop and review it; our guide on what to do if low FODMAP doesn't work walks through that review.

If you have methane-dominant overgrowth (IMO)

Methane-dominant overgrowth tends to come with constipation rather than diarrhoea, and that changes the diet calculation. The 2025 nutrition review warns that in IMO it is critical to keep fibre intake adequate to avoid worsening constipation, which is hard because many high-fibre foods contain FODMAPs (Velasco-Aburto 2025). Our article on whether fiber makes IBS worse explains how different fibres behave.

The evidence also suggests methane is harder to shift. In the IBS group of the gas study, methane did not differ between the low and high FODMAP diets (Ong 2010), and in the elemental diet trial, normalisation was lowest in the IMO-only group (58%) (Rezaie 2025). Both are small numbers.

If you have Crohn's disease or ulcerative colitis as well, the diet question has extra layers, especially with strictures or after surgery. Our article on whether low FODMAP is good for Crohn's covers the IBD side; discuss any restrictive diet with your IBD team first.

A worked example: same breath test, two reasonable plans

These are illustrations, not case reports.

Person A has a hydrogen-positive breath test, loose stools and bloating, and has just finished an antibiotic course. Their symptoms are better but not gone. They have tried nothing dietary yet. With a dietitian, they start a low FODMAP elimination for a few weeks because it is the approach with trial evidence for symptoms. Bloating improves. They move into reintroduction, find onion and large portions of wheat bother them while lactose and stone fruit do not, and settle on a diet that avoids only a few things. They log symptoms throughout so the reintroduction results are based on records rather than memory.

Person B has a methane-positive test, constipation, and has already spent a year on a strict low FODMAP diet with little benefit and some weight loss. More restriction is the wrong move. Their clinician reviews whether the diagnosis fits, and their dietitian focuses on restoring weight and fibre that does not worsen their symptoms. They try spacing meals but abandon it because it makes it too hard to eat enough. The low fermentation list is discussed, but since it would remove oats and some vegetables they currently tolerate, they use only parts of it.

The breath test was positive in both, and the right dietary plan was almost opposite. That is what the evidence actually supports: diet in SIBO is about symptoms, tolerance and nutrition, tailored to the person.

A practical walkthrough

1. Settle the diagnosis question first. If you are not sure your symptoms are SIBO, read SIBO vs IBS symptoms and raise it with your doctor. Diet will not tell you the answer.
2. Ask for a dietitian. Both the IBS literature and the SIBO reviews stress dietitian support, and it matters more the more restrictive the diet.
3. Pick one approach, not a mash-up. Running low FODMAP and the low fermentation list at the same time leaves very little to eat. Choose one starting framework with your dietitian.
4. Set a time limit before you start. Decide when you will review progress, typically a few weeks into elimination.
5. Log symptoms and food in real time. Reintroduction only works if you can see which food was followed by what, and reactions can be delayed. Clairop is built for this: it checks each logged food against delay windows of up to three days, and you can see how it works.
6. Watch your weight. If it is falling without intent, tell your doctor and dietitian.
7. Reintroduce, and keep reintroducing. The goal is the broadest diet you can tolerate, not the cleanest list.

Myths about SIBO diets

"Low FODMAP treats SIBO." It reduces hydrogen production and often symptoms. The only randomised data on clearance come from a handful of people in one IBS trial, with no untreated comparison, which cannot show that the diet cleared anything.

"The low fermentation diet is the proven SIBO diet." We found no published trial of it. Its food list is a design, not a test result.

"If the prep diet makes me feel great, I have SIBO." The prep diet removes fermentable material for everyone. It lowers gas whether or not you have overgrowth.

"You need to stay on a SIBO diet forever to stop it coming back." Diet for maintaining remission has not been rigorously studied. Any long-term diet should be the broadest one you tolerate.

"The elemental diet works 100% of the time." That figure comes from six people with hydrogen SIBO in one uncontrolled trial. Overall normalisation was 73% in that trial and 80% at day 15 in the earlier one, with no control groups.

"Eating fibre during SIBO treatment is always wrong." The one trial we found of adding a fibre supplement to an antibiotic found higher eradication, not lower. It was small, and it is not a reason to change treatment without your prescriber.

When to see a doctor promptly

Diet changes are not the right response to any of these. See a doctor promptly if you have:

• Blood in your stool, or black, tarry stools
• Unintended weight loss, or weight loss you cannot stop on a restricted diet
• Fever, or symptoms that wake you at night
• Iron deficiency anaemia or other deficiencies on blood tests
• New bowel symptoms starting after age 50, or a family history of bowel cancer or inflammatory bowel disease
• Persistent vomiting, or signs of bowel obstruction such as severe swelling and being unable to pass wind
• Symptoms that keep returning after treatment, which may point to an underlying cause worth investigating

Recurrent SIBO often has an underlying cause, such as slowed motility, previous surgery, or another condition, which the AGA practice update says management should focus on finding (Quigley 2020).

The short version

Low FODMAP is the better evidenced diet, but its evidence is in IBS; in SIBO it is a reasonable symptom tool, not a treatment. The low fermentation diet is a different, untested theory about where fermentation happens, and the company behind it also makes the formula tested in the main recent elemental diet trial and part-funded that trial. The elemental diet is the only dietary approach studied specifically for clearing overgrowth, in two small uncontrolled studies. Whatever you choose, keep the restriction short, reintroduce foods systematically, watch your weight, and do it with a dietitian. And if you want to understand the foods themselves, our guide to what FODMAP stands for breaks down each group.