What is Small Intestinal Bacterial Overgrowth (SIBO) and How Do You Know If You Have It

What is Small Intestinal Bacterial Overgrowth (SIBO), and How Do You Know If You Have It?

Millions of people worldwide nowadays are suffering from some kind of “gut issues” which, at first glance, might seem to be irritable bowel syndrome (IBS). (Constipation, diarrhea, abdominal pain, gas, bloating, heartburn, nausea, etc.… the struggle is real!)

But what I’m finding in my functional nutrition clinic (after digging deeper) is that many people who were diagnosed with “IBS” actually have an underlying case of small intestinal bacterial overgrowth (SIBO).

In this article you’ll learn what SIBO is, what causes it, how to recognize the classic telltale signs and symptoms of SIBO vs IBS, how to test for it, and more importantly – what you can do about it if you do have it.

Disclaimer:  This article is meant to be educational and informative. It is not medical advice. Please consult your doctor and a registered dietitian if you suspect you might have SIBO!

What is SIBO?

Contrary to Shakespeare’s famous “What’s in a name?” proclamation, SIBO is exactly what it sounds like:  small intestinal bacterial overgrowth.

In other words, it means that bacteria have migrated up from your colon, into your intestines.  And they don’t belong there!

  • When microbes enter the small intestine, they take it upon themselves to start feasting on (and subsequently fermenting) undigested / partially digested food particles.  This produces methane and/or certain types of hydrogen gas as a byproduct.

The consequence of microbes living, growing, and fermenting food in your small intestine is a slew of unwanted symptoms which often masquerade as IBS, flying under the radar for too long and wreaking havoc in your system. (1)

Signs & symptoms

When it comes to SIBO, the cluster of symptoms you experience and the foods you can/can’t tolerate will be unique to you, but can include any or all of the following:

  • Diarrhea (too-frequent, to-soft, loose bowel movements) 
  • Constipation (too hard, strained, incomplete, and/or infrequent bowel movements)
        • …aka Bristol 1’s and/or 2’s
  • Gas ~45-60 minutes after eating
  • Bloating / abdominal distention  ~45-60 minutes after eating
  • Stomach pain
  • Nausea
  • Heartburn
  • Vitamin/mineral deficiencies
  • Food intolerances (i.e. lactose, wheat, fructose, and/or other high FODMAP foods, and/or high sucrose foods, and/or high sulfur foods)

Signs and Symptoms of SIBO - infographic

Primary types of SIBO

While everyone’s SIBO will manifest differently case-by-case, there’s still usually some degree of overlap based on the type(s) of SIBO people have.

(Yup – unfortunately it’s possible to contract more than one type of SIBO! In all three types, you’ll likely notice signficant relief from following a low FODMAP diet.)

  1. Methane-dominant (usually presenting with constipation, gas, bloating, and weight gain)
  2. Hydrogen-dominant (usually presenting with diarrhea, gas, bloating and abdominal cramping)
  3. Mixed (methane + hydrogen)

SIBO sub-types

(Read more about SIBO types and sub-types here!)

Types and Subtypes of SIBO - Infographic

What causes it?

SIBO is complex, and unfortunately lots of different types of issues can lead to bacterial overgrowth in the small intestine if left unchecked for too long.

This list isn’t exhaustive, but it’s still pretty extensive!  I find that usually it’s not just one thing but rather a combination or culmination of multiple things over time, which will lead to SIBO:

  • Low stomach acid (enables the growth of bad bacteria in the intestines)
    • This can be caused by lots of medications – not just acid blockers / proton pump inhibitors!
  • H.pylori infections
  • Too-slow gut transit time / slow motility
    • Poor motility interferes with your gut’s ability to “sweep” the bacteria back down from your intestines into your colon.  
    • Motility issues are usually the result of a miswired enteric nervous system, secondary to any of the following:
      • Parkinson’s
      • Postural Orthostatic Tachycardia Syndrome (POTS)
      • Nerve damage from diabetes
      • Head injury / concussion
      • Hypothyroid
      • Snacking all day (reduces Migrating Motor Complex which is responsible for gut motility)
      • Sipping on artificially-sweetened / stevia-sweetened beverages all day (shuts off Migrating Motor Complex & reduces gut motility)
      • Chronic stress (shuts off the Migrating Motor Complex & compromises gut motility)
      • Food poisoning / acute gastro-infection (E. coli, shigella toxin, Salmonella, C. diff, etc.)
        • These “bad” pathogenic microbes all release an endotoxin called “Cytolethal distending toxin B” / “CDBT”
          • …which creates an autoimmune attack on your Migrating Motor Complex (the part of your gut’s enteric nervous system responsible for your gut motility)

Okay, that’s probably TMI and more than you care to know! But these things matter. (These are all examples of the types of things I help my clients investigate at a deeper level in my clinic.)

Understanding the “Why” (aka your root-causes) behind the “What” (in this case, SIBO) is key to cracking your code and addressing long-standing, stubborn gut issues in my field of holistic and functional nutrition!


In my nutrition practice and through extensive continuing education, I’ve also learned that many people who have SIBO are also statistically more likely to have any of the following “SIBO comorbidities” – in no particular order:

  • Leaky gut syndrome
  • Dysbiosis
  • Candida overgrowth
  • Inflammatory bowel disease (celiac, diverticulitis, Crohn’s, ulcerative colitis)
  • Diabetes
  • Parkinson’s
  • Sjogren’s syndrome
  • Hashimoto’s (autoimmune hypothyroidism)
  • Fat-soluble vitamin deficiencies
  • B vitamin deficiencies
  • Iron deficiency anemia
  • Non Alcoholic Fatty Liver Disease
  • Lactose intolerance (with or without dairy sensitivity)
  • Fructose intolerance
  • Sucrose intolerance (acquired type)
  • Food sensitivities
  • Ehlers Danlos syndrome
  • Postural Orthostatic Tachycardia Syndrome (POTS)
  • Mast Cell Activation Syndrome (MCAS)

It’s not always clear which came first (the chicken or the egg), but the main takeaway is these types of things are all interconnected, and should be treated as such.

SIBO vs IBS – how can you tell?

While there’s a TON of overlap between SIBO and IBS symptoms, there are also a few telltale signs and clues of SIBO that you should keep a lookout for.

It’s likely SIBO if…

  1. You’ve had adverse reactions to probiotics / prebiotics – they actually make you MORE gassy and bloated!
  2. The bloating is happening at baseline every single day (no intermitent freedom from bloating), and it gets worse in the afternoons and evenings.
  3. You had a low elastase level on a comprehensive stool analysis test – this is something I see a lot when people have low stomach acid, which is a common root-cause of SIBO.
  4. You feel much better on a low FODMAP diet.
    While this can also be the case for many people with IBS, usually when someone is reacting to multiple types of FODMAPs, it’s a clue that you likely have SIBO.  (Up to 78% of people with IBS actually have SIBO!) (2)

It’s likely hydrogen sulfide SIBO if…

  1. You have diarrhea, gas, and bloating – and saw a flatline on your SIBO breath test…AND:
  2. A low FODMAP diet isn’t helping (you have a sulfur intolerance).
  3. You feel worse when eating sulfur-producing foods/supplements (garlic, onions, dried fruit, wine, N-acetyl-cysteine, etc.).
  4. You have gas/stools that smell of rotten eggs.
  5. You experience body pain and feel “toxic”.
  6. You have numbness/tingling in your extremeties.
  7. You’re prone to bladder issues.
  8. You are sensitive to light and noise.

Telltale Signs and Symptoms of Hydrogen Sulfide SIBO - infographic

How to test for it:  SIBO breath testing

If you suspect you’ve got SIBO, you may want to run a SIBO breath test.  This is something you can usually do through your GI doctor.

But you can also order this online, if for any reason your doctor doesn’t want to order this test. (Unfortunately I see that happen a lot!)

To be clear, I know SIBO tests are a pain, a hassle, and an inconvenience. Not to mention, they aren’t 100% accurate and they aren’t perfect…

But they can still serve to help you and your treatment team to gain clarity and determine what the next steps will be on your journey from a medical/nutritional standpoint.

(I’ve also seen people treat their dysbiosis first, and then the SIBO went away. So a SIBO test isn’t always necessary.  There’s a lot of overlap in SIBO and dysbiosis protocols!)

How to address SIBO:  holistic & functional nutrition interventions

From a 10,000-foot overview, you’ll want to work with a functional dietitian and/or holistic nutritionist who specializes in SIBO (alongside a GI doctor), so you can work your way through a customized variation of the 5R protocol for gut repair.

(This is also something I teach people how to do in my online program, the Complete Gut Repair Roadmap!)

An example of a 5R protocol for SIBO may entail the following:

  1. Remove whatever’s feeding those “bad” microbes, so you can starve them out (if you don’t have an eating disorder).  This is usually via a customized or modified version of 6-phase low FODMAP/low sulfur elimination diet.
  2. Replace whatever you aren’t getting (but want/need) from a food & micronutrient standpoint, via the right dietary modifications, swaps, and vitamin/mineral supplements as needed.
  3. Rebalance your gut microbes.
    1. This means killing off “bad” pathogenic microbes in your intestines, usually with an antibiotic such as Xifaxan (Rifaximin) or a custom combination of evidence-based herbal antimicrobials, probiotics, and prokinetics.
    2. You’ll also want to make sure you’re repleting and feeding your healthy probiotic microbes via the right prebiotics and probiotic foods/supplements for SIBO to meet your individual needs.
  4. Repair your gut lining with the right functional foods/supplements/herbs.
    1. This is something most people tend forget about, but tt’s an important step!  This is what’s going to help you build resilience so you can eventually enjoy more foods without reacting.
  5. Rebalance your lifestyle.
    1. This could mean reducing stress, increasing movement, getting on a better sleep schedule, or something else! It’s all about living more holistically so you’re giving yourself the best possible shot at staying in remission.

SIBO nutrition FAQ’S

Is SIBO treatable?

Yes! Luckily in most cases, SIBO is mostly “figureoutable.”  But by no means is it easy. Some but not all of my clients who’ve had SIBO are in remission, because it takes a lot of work and a ton of commitment.

That said, don’t expect to resolve your SIBO after just a few consultations with a doctor or dietitian… it doesn’t work that way. You’re going to need to commit to moving through each of the above 5R protocols with your treatment team, at your own pace!

How long does it take to heal from SIBO?

Every body is different, and not everyone will get the same level of results.  But the bare minimum amount of time I’ve seen somebody heal from SIBO in my clinic is realistically ~3 to 6 months, if their case is not too complex and if they’re really consistent with sticking to recommendations (at least 90% of the time).

If you aren’t in the right mindset, and you just want a quick fix, with all due respect… you may not have a whole lot of success on a SIBO recovery journey. It’s not for the feint of heart!

Can I resolve SIBO just from diet changes?

Nope.  While you may feel a whole lot better on a low FODMAP diet (especially if you have SIBO), unfortunately small intestinal bacteria can’t just be starved out this way!

You’ll need a more aggressive intervention (with the right types of antibiotics via medicine and/or herbal antimicrobials).  This type of intervention also needs to happen in a very time-sensitive, systematic way, under the clinical supervision of a doctor and a holistic / functional registered dietitian.

Does everyone with SIBO need to go on a low FODMAP diet?

Yes and no!  While a low FODMAP diet is the most common diet to serve as a nutritional “backbone” or general framework for many people with SIBO, your dietary protocols will be 100% unique and customized to YOU.

I’ve also worked with clients who had a great deal of success and felt a lot better on variations of the Gut & Psychology Syndrme (GAPS) diet and/or Paleo diet for their SIBO/IBS.

Your prescribed dietary protocols will be based on your food preferences, adverse food reactions, type(s) of SIBO, your relationship with food, and any other SIBO comorbidities you may have going on.

Take my word for it – please don’t try to figure this out without consulting a registered dietitian. 😉

Is it possible to have SIBO and IBS at the same time?

Yes.  If you notice you still have IBS symptoms after treating SIBO, you and your treatment team should consider ruling out other things like dysbiosis, candida overgrowth, food sensitivities, and a miswired nervous system/stress response and then reassess.

(You also may want to look into IBD if you don’t feel better after looking into and addressing the above stuff that I see most often among people with IBS!)

More resources

Small intestinal bacterial overgrowth: final thoughts

SIBO (small intestinal bacterial overgrowth) is one of the most common IBS “imposters” wreaking havoc on people who suffer from “gut issues.”

It looks and feels like IBS, but it’s unique in that the symptoms are caused by “bad” microbes in your intestines, fermenting certain types of foods you eat (especially those higher in FODMAPs).

SIBO can be caused by lots of different lifestyle factors and certain conditions which negatively impact gut pH (acidity level), the nervous system / gut motility, and overall microbial growth. When those things are out of balance and left unchecked, it enables the growth of bad bacteria in your intestines (and often the colon, too).

There are very specific medical, nutritional, and herbal protocols which can help you to address SIBO holistically. You’ll need to consult a doctor and functional dietitian who specialize in SIBO to receive custom protocols, since one size does not fit all, and a low FODMAP diet is not enough to “fix” small intestinal bacterial overgrowth.

If you’d like to learn more about this and learn more from me on a weekly basis via my email newsletters, please feel free to download a copy of my free gut health nutrition guide:

5 Diet Mistakes to Avoid When Healing Your Gut!

XO – Jenna

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