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Is Testing for SIBO Helpful? Maybe Not So Much

Written by Dr. Michael Ruscio, DC on November 13, 2024

Written by Dr. Michael Ruscio, DC on November 13, 2024 — Reviewed by Hilary Watts

• What Is SIBO and What Causes It?|
• How To Test for SIBO|
• Why I Don’t Recommend SIBO Breath Tests|
• How To Treat SIBO|

If you’re having a lot of unpleasant gut symptoms such as gas, bloating, diarrhea, or abdominal pain, there’s a possibility that you may have SIBO, aka small intestinal bacterial overgrowth.

This form of dysbiosis (gut microbiome imbalance) occurs when you have too many bacteria growing in the small intestine—a place where they shouldn’t flourish—causing the symptoms mentioned above, and possibly more.

The good news is that SIBO responds well to natural and conventional treatments. 

But how do you know if you have this condition? And do you need a definitive diagnosis in order to treat it? 

In this article, I’ll share with you my experience with SIBO testing and its usefulness. Then I’ll walk you through the simple treatment plan we use in the clinic—it works to improve gut health, regardless of what’s behind our clients’ SIBO-suggestive symptoms.

What Is SIBO and What Causes It?

Small intestinal overgrowth (SIBO) is when the small bowel has higher amounts of bacteria than normal 1.

Some people will get significant symptoms from having too many bacteria in the small intestine, whereas others will react less. 

Gastrointestinal symptoms common in SIBO usually result from the bacterial buildup causing excessive fermentation and gas production in the intestines. Gas in the small intestine can cause the following SIBO symptoms 1:

• Bloating/distension (expansion) of the belly
• Flatulence (farting)
• Cramps
• Diarrhea
• Constipation

SIBO can also cause non-gut symptoms including: 

• Chronic fatigue 2 
• Poor mood 3 
• Brain fog 4
• Restless legs 5
• Skin conditions like rosacea and psoriasis 5

These wider symptoms likely occur because SIBO is an infection that can activate your immune system. Your small intestine contains the greatest density of immune cells in your body. So, a bacterial overgrowth there chronically activating your immune system can lead to inflammation and symptoms across all body systems 6. 

Inflammation in the gut can also mean you absorb fewer nutrients, which can worsen immune dysregulation and resulting symptoms.

Factors that may contribute to developing SIBO include 7: 

• Gut dysbiosis 
• Reduced stomach acid
• Gut structure abnormalities or motility (digestive tract movement) problems, caused by conditions like:
  • Gastric bypass surgery 
  • Celiac disease
  • Inflammatory bowel disease (IBD), typically Crohn’s or ulcerative colitis 
  • Irritable bowel syndrome (IBS) (SIBO is common in people with IBS, and the symptoms often overlap) 8
• Living with diabetes, hypothyroidism, or obesity 9 10

How To Test for SIBO 

If you have symptoms that are suggestive of SIBO, or if you have gut issues and are at high risk of SIBO, it makes sense that you might want to get tested for SIBO.

The two main types of tests are:

1. Sample collection directly from the small intestine (small intestinal culture or aspirate)
2. Breath tests, e.g. hydrogen breath testing

Direct Sampling

Having a sample taken that directly measures the number of bacteria in the small intestine can give the most accurate diagnosis of SIBO. 

Depending on the location within the small intestine, a normal amount of bacteria is between 10,000 and 100 million colony-forming units per milliliter (CFU/mL). Anything higher than this found in a small intestinal aspirate means you have SIBO. 

Fun fact: The normal numbers of bacteria in the small intestine are at least 10 times less than the typical concentration in the large intestine 1.

Unfortunately, giving a sample of your small intestinal contents is invasive and expensive (upwards of $1,500 if you don’t have health insurance) and not always accurate 11. You would only have a SIBO test done this way if you were already getting an upper endoscopy (tube from the mouth down into the first part of the small intestine) for some other reason, and your gastroenterologist suspected an overgrowth.

That said, if you have symptoms suggestive of SIBO and you happen to have an upper endoscopy scheduled, you can ask the gastroenterologist if they’ll do a SIBO culture at the same time, for the most definitive results. 

Breath Testing

Breath tests for SIBO are more common and much easier to do 11. However, they are also less reliable and can still be expensive (e.g. $199 to $350 without insurance). There are many such tests available to buy on the internet, and your doctor can help you choose a reliable one.

The two types of SIBO breath tests use lactulose or glucose to measure the gas coming from your small intestine 12. 

With both tests, you’ll drink a sugary liquid (lactulose or glucose) and, at prescribed intervals afterward, you’ll breathe into a device that captures the gas from your lungs into test tubes. 

You’ll then send the multiple tubes of breath samples to a lab for analysis and wait for the results. The gases they’ll focus on measuring include hydrogen and methane.

Although both test kits are similarly accurate, the glucose test appears to have fewer false positives than lactulose, meaning it’s less likely to say SIBO is present when it’s not 13. Glucose doesn’t reach the large intestine, which is naturally very gaseous—less gas from the colon may help reduce false positives 12.

To minimize false positives from a lactulose test, the window for testing gases in the breath shouldn’t go beyond 80–90 minutes. Results beyond 90 minutes are more likely to show false positives for SIBO because they start measuring elevated gas levels from the large intestine rather than just the small intestine 12. 

Overall, both breath tests can help diagnose SIBO as long as someone interprets them skillfully. However, it’s worth knowing that test results and symptoms don’t always correlate 14. For example, 

• Your SIBO test could be negative (saying no SIBO is present), even though you actually have SIBO or symptoms that suggest it 14.
• You could test positive for SIBO but not have any SIBO-typical symptoms. In other words, it’s possible to have SIBO without any symptoms (asymptomatic SIBO), or to have SIBO secondarily to a condition which causes non-SIBO-like symptoms that stand out more than your gut symptoms. Both situations would make you less likely to test for SIBO in the first place 15. 

Why I Don’t Routinely Recommend SIBO Breath Tests 

A positive SIBO test result can be helpful to confirm that bacterial overgrowth is likely behind your gut symptoms.

But as we’ve seen above, your SIBO test result does not always accurately correlate with how sick you feel, and false negatives (results showing no SIBO though you have it) are also possible.

After evaluating published research and my clinical experience over the years, I no longer routinely recommend diagnostic tests for SIBO.

The main reason I find SIBO testing isn’t worthwhile is that the results make no difference to how my clients move forward. That means they can benefit from the same gut-health treatments, regardless of whether they test positive or negative for SIBO. 

The most disheartening examples that contribute to my position on this are people whose negative SIBO tests stood in the way of them getting helpful treatment for their SIBO-like symptoms.

The bottom line? Whether your gut suffers from SIBO, a fungal overgrowth, leaky gut, or some other condition related to microbial imbalance, you have a good chance of benefiting from a well-rounded treatment plan to bring your gut back to health.

How To Treat SIBO 

 As a food-first healthcare practitioner, I generally recommend that my clients start by tackling their gut symptoms with diet. 

Given the huge overlap between SIBO and IBS symptoms (up to 40% of people with IBS likely have SIBO 8), I generally recommend that my clients jump straight in with a low-FODMAP diet.

A Low-FODMAP Diet

FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols, which are short-chain carbohydrates (sugars) that the small intestine can’t absorb well. Examples of high-FODMAP foods include onions, garlic, dairy products, legumes, wheat, pears, and dried fruits.

Some people experience digestive distress after eating high-FODMAP foods, especially if they have IBS or SIBO (or both), which is why a low-FODMAP diet can be useful for gut symptoms. 

Indeed, multiple meta-analyses (high-quality studies of studies) have determined that a low-FODMAP diet can improve overall digestive symptoms, abdominal pain, and quality of life in people with IBS-type symptoms 16 17.

There is far less research looking at how a low-FODMAP diet affects SIBO specifically. However, one recent clinical trial showed a 30% reduction in SIBO (as measured by breath gases) after just two weeks of removing FODMAPs from the diet 18. Another clinical trial found that a low-FODMAP diet was effective for IBS patients whether or not they had SIBO 19.

When you get started with the low-FODMAP diet, it’s ideal to work with a skilled dietician or nutritionist who will give you a reliable list of which high-FODMAP foods to remove and which foods to include. Here is a summary list of low-FODMAP foods:

You can also download this useful app to help with the elimination process and navigate the reintroduction phase that follows.

For suspected SIBO, I recommend that my clients eliminate FODMAPs for 4–6 weeks to give the diet a fair test. 

Some who try the low-FODMAP diet find it calms their symptoms significantly—they are often tempted just to stay with the restricted diet because they don’t want their symptoms to return. 

Ultimately, though, our goal is to achieve a more nutritionally varied diet by reintroducing higher-FODMAP foods one by one and figuring out their tolerance level to each food. There is no need to rush things—recent research suggests it’s probably safe to stay on a balanced low-FODMAP diet for up to a year 20. 

Probiotics

The other main strategy that helps to get rid of SIBO and soothe symptoms is to take a probiotic. I almost always recommend that my clients do this while they trial a low-FODMAP diet.

Here’s why: In the clinical trial I mentioned of a 2-week low-FODMAP diet for SIBO , adding the probiotic S. boulardii on top of dietary changes ramped up SIBO improvement from 30% to 40% 18.

Several more studies show probiotics can be very effective in treating SIBO. Indeed, one meta-analysis of 18 studies showed that probiotics of many varieties and strains eradicated SIBO in about 53% of people who took them 21. 

A 2019 clinical trial also found that probiotics were more effective for GI symptoms in people with SIBO than without 22. This puts to bed the argument you may have heard that probiotics aren’t good for people with SIBO.

Probiotics may reduce SIBO (and help microbiome health in general) by 21: 

• Reducing leaky gut and inflammation 
• Resolving dysbiosis (bacterial imbalances) and fungal overgrowths 
• Improving gut motility 
• Improving the gut-brain connection, limbic system (brain structures that regulate how we feel, act, get motivated, and remember things), and stress response

After they experiment with a low-FODMAP diet and probiotics for 4–6 weeks, I coach my clients to assess their progress. If their symptoms don’t improve, it may be time to consider a course of antibiotics or herbal antimicrobials.

Antimicrobials

Rifaximin (brand name Xifaxan), is the conventional antibiotic (a type of antimicrobial) used the most for addressing SIBO. This antibiotic may eradicate SIBO in up to 50–60% of infected patients 23 24, but its costliness and lack of coverage by some insurance plans may pose challenges. 

On that note, some insurers will cover your prescription for rifaximin if you have a confirmed positive SIBO result from a breath test. This is one instance where it can be useful to get tested.

In any case, rifaximin may reduce GI symptoms, regardless of whether SIBO is causing them. For example, in one study, the antibiotic appeared to improve GI symptoms, even when the participants had a negative SIBO test before they took it. Symptoms also improved with rifaximin, whether the drug got rid of SIBO or not 25. 

This all adds support to my previous point that the same gut-supportive treatments can help, no matter what type of gut microbiome imbalance we have. If our symptoms suggest SIBO, we’re probably better off using effective treatments—rather than a breath test—to guide our treatment and gauge our success.

Natural Antimicrobials

If my clients can’t get or don’t want to use the conventional antibiotic rifaximin, natural antimicrobials are a useful workaround that can be about as effective against SIBO.

For example, 

• A study found that herbal antimicrobials eradicated SIBO in 46% of patients, which was a higher success rate than rifaximin in this particular study 26. 
• In a clinical trial our team conducted, herbal antimicrobials successfully eradicated SIBO in approximately 40% of patients. 

Oregano oil is an herbal antimicrobial that is particularly beneficial due to its wide-reaching antimicrobial properties. Its broad-spectrum effects may allow oregano to help gut symptoms even if SIBO isn’t confirmed. In other words, it can help to clear the gut of unwanted microbes, such as overgrowths of bacteria, fungi, or parasites 27 28.

Other effective herbs you may see in an herbal antimicrobial formula are berberine 29 30 and sweet wormwood 31 32. 

The primary distinction between herbal antimicrobials and antibiotics like rifaximin lies in their time frame for effectiveness. While rifaximin typically yields results within 10–14 days, herbal antimicrobials require at least a month to demonstrate benefits 26. 

However, herbal antimicrobials are gentler on the body and do not appear to contribute to bacterial resistance in the same way as conventional antibiotics 33.

Antibiotics and Probiotics Are a Perfect Double Act

Taken together (though ideally at opposite ends of the day), probiotics and antimicrobials can be a dream team when it comes to clearing SIBO and improving symptoms. As you may recall, probiotics and rifaximin taken individually can each reduce SIBO by around 50% 21 23 24. 

However, when rifaximin and probiotic supplements are taken together, the eradication rate can rise to as high as 86% 21. Taking probiotics alongside antibiotics can also help to prevent antibiotic-related diarrhea 34.

An Elemental Diet

Another option for taming SIBO symptoms is an elemental diet, which is a liquid hypoallergenic diet that provides all the nutrients we need in a partially digested form.

An elemental diet is largely devoid of the carbs and prebiotic fibers that feed bacteria in the small intestine. As such, the diet can feed you while starving any excess bacteria growing there.

For some people, moving over to an elemental diet for a short period can be the best fix for their SIBO symptoms. A 2004 clinical trial with 93 patients found that a 2-week elemental diet may have eradicated SIBO in 80% of them 35. 

However, the elemental diet isn’t for everyone, and I generally recommend that my clients try the low-FODMAP and probiotics route first. 

When my clients are sure they want to commit to the elemental diet as their main SIBO treatment, I coach them on using this therapy exclusively for 1–3 weeks. This is about the right amount of time to kill significant bacterial overgrowths.

However, most of my clients use an elemental diet to boost their SIBO treatment (low-FODMAP diet, probiotics, and antimicrobials), and for them 4 days is the maximum term I suggest.

It’s also an option to use elemental shakes as partial meal replacements. When my clients with SIBO opt for this, I guide them to replace breakfast and lunch with an elemental shake, and then put more effort into planning an enjoyable low-FODMAP dinner.

Treating Is More Important Than Testing

Think you might have SIBO? Spending a lot of money on diagnosing it is probably unnecessary when a simple and safe gut health regimen can usually have a big positive effect on your symptoms.

Knowing about the options I’ve outlined—a low-FODMAP diet, probiotic therapy, and perhaps antimicrobials or an elemental diet—you now have a lot of power in your hands. If SIBO or something else is producing uncomfortable symptoms, like gas, diarrhea, bloating, and brain fog, improving your microbiome health with your healthcare provider’s support will likely help. 

But if you still can’t get on top of suspected SIBO, don’t fret. You can check out my book, Healthy Gut, Healthy You, which dives deeper with the Great-in-8 gut-healing protocol, or you can contact us at the Ruscio Institute for Functional Health to schedule an appointment.

The Ruscio Institute has developed a range of high-quality formulations to help our clients and audience. If you’re interested in learning more about these products, please click here. Note that there are many other options available, and we encourage you to research which products may be right for you. The information on DrRuscio.com is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.