SIBO and IBS: What Do You Need to Know?

Small Intestinal Bacterial Overgrowth (SIBO) is a condition that has been acknowledged by alternative and functional medicine doctors for several years now but it is just gaining traction in the traditional medical world. There is still so much we don’t know about this condition yet, but if you have IBS and aren’t familiar with SIBO, this article is for you.

What exactly is SIBO and how does it relate to IBS?

Typically, we have trillions of bacteria in our large intestine (normal, healthy stuff), but a much smaller number in our small intestine. When SIBO is present, an overgrowth of bacteria occurs in our small intestine (hence the name) where it doesn't belong and can lead to a myriad of digestive symptoms like bloating and distention (that "6 months pregnant" look), diarrhea, constipation, gas, and abdominal pain. As you can see, the symptoms are very much those of IBS! I've read estimates that anywhere from 4-78% of people with IBS have SIBO. This high variability in numbers is likely related to the lack of consensus on most accurate diagnostic testing methods and standards.

Testing for SIBO

Most commonly, breath testing is done to look for the presence of SIBO, however this test has its limitations. One of the biggest problems is that false positives and negatives are possible depending on the speed of one’s digestive system and on the test sugar used. Additionally, some people may produce hydrogen sulfide gas, which can't currently be measured through breath testing (though this technology is in development at Cedars-Sinai!). This is one reason it's super important to find a center or a doctor who is very skilled in administering and reading SIBO test results.

There is a prep time of 24 hours before the breath test, which includes 12 hours on a special, restrictive diet, followed by 12 hours of fasting. On the prep diet, no sugar of any kind is allowed, no fruits, vegetables, or grains except for white rice and white bread. If you are gluten free, you will need to rely on white rice for your only carbohydrate source that day. To my knowledge, gluten free breads have not been approved on the SIBO prep diet, but check with your provider first. Proteins allowed include only meats and eggs, so if you are a vegetarian be prepared to eat a lot of eggs that day.

It is extremely important that you follow the prep diet exactly as prescribed by your doctor or per the instructions that come with the test (if you are doing the test at home). Do not make any exceptions to the diet or your test is pretty much guaranteed to yield inaccurate results! Also note that certain medications such as probiotics and antibiotics must be stopped for a certain period of time before you take the test, so please refer to the instructions you receive. You can't exercise or smoke on the morning of the test either or it will alter the results.

Once you start the test, you will blow air into a tube to get a baseline reading. You then drink a non-absorbable sugar lactulose, or the sugar glucose, which will feed the bacteria and encourage them to make gas. When the gas is produced, it will diffuse across the bloodstream and travel to the lungs where it is expired through your breath. You will then blow into a tube every 20 minutes over a two to three hour time period which will capture this gas. Just be aware that the lactulose may stimulate diarrhea.

The closest there is to a "gold standard" test for SIBO is a small intestinal biopsy with aspirate but, of course, a biopsy is invasive and costly. So it is not routinely done, at least not in the US. Also note at this time stool testing cannot be used to diagnose SIBO. This makes breath testing the most available and cost effective option.

There are no blood tests to look for SIBO specifically, however, certain blood tests can indicate the presence of malabsorption that may occur with SIBO. For example, Vitamin B12 as well as certain fat soluble vitamins like A, D, and E may be decreased due to the bacteria consuming the vitamins or due to fat malabsorption. Alternatively, folate levels or B12 could be elevated because SIBO bacteria can actually produce these vitamins.

So what is a person to do to get a SIBO diagnosis?

I know that many doctors now will just treat for SIBO, regardless of whether a person was tested or not. It is sometimes necessary to try it, especially if other treatments have failed to provide adequate symptom relief. As I mentioned previously, it's important that you have an experienced healthcare practitioner working closely with you to get a diagnosis and come up with a treatment plan based on your whole clinical picture and symptoms.

Please do not diagnose and treat yourself for SIBO! I do know it is easier said than done to find a doctor that is a good fit, or that will even test for SIBO, but they are out there! Ask on Facebook groups or online IBS forums for doctor recommendations or read reviews online before booking an appointment. The website can be a helpful resource for doctor reviews.

Treatment options for SIBO


Xifaxan (or Rifaximin) is an antibiotic that is thought to be localized to the gut and so doesn't cause any other systemic side effects (like yeast infections). Xifaxan is typically given three times daily for 14 days. A word of caution that this medication can be extremely expensive depending on your insurance coverage, and it's not currently FDA approved for the treatment of SIBO, only for IBS-D.

There are certain herbal antibiotics that may be effective for SIBO, such as a combination of Dysbiocide and FC Cidal or Candibactin-AR and Candibactin-BR. Typically the herbal treatments need to be taken longer than antibiotics, often for a month or more.

Diet for SIBO

If you look online for SIBO diet options, you will likely find yourself overwhelmed in is a sea of unproven recommendations. There are about as many dietary remedies for SIBO as there are flavors of ice cream. Some of the most common ones are the Low FODMAP diet, an elemental diet (must be followed only under guidance of a physician), Specific Carbohydrate Diet (SCD), SIBO Specific Diet (combined SCD and Low FODMAP), Fast Track, and the Cedars Sinai Diet. It is important to know that there is no research based diet proven for the treatment of SIBO at this time.

The name of the game for SIBO is reducing fermentation and getting symptoms to an acceptable level for the patient. A low FODMAP diet is one such low fermentable diet, however sometimes people with SIBO react to grains, even white rice, as well as raw vegetables. Therefore, sometimes other modifications need to be made to carbohydrates, which is where these other diets may come into place. As you can see, this is another reason to work one-on-one with a healthcare provider and dietitian to help you with an individualized diet plan. I tend to have my patients try low FODMAP first, because it is the least restrictive of many of these diets, and I’ve seen good success with it clinically in my own practice and among my colleagues.

Diet change alone often is not enough to cure the SIBO, so traditional or herbal antibiotics are usually needed in addition. It's often not recommended to start on a low fermentable diet until after antibiotic treatment is complete, because of a theory that the bacteria go into hibernation on these diets and need to be brought out to be eradicated more efficiently. It is just a theory as of yet, but I typically advise my clients to enjoy a few high FODMAP foods during antibiotic treatment, and then to start Low FODMAP elimination afterwards for a period of 4-8 weeks before reintroducing FODMAPs.

Causes of SIBO

There are many possible causes of SIBO, including motility issues, autoimmune disorders like lupus, celiac disease, hypothyroidism, conditions like diabetes, ileocecal valve malfunction, low stomach acid (including from prolonged use of proton pump inhibitors), IBS, IBD, or prior bowel surgery. This is not an exhaustive list, but if you have any of these conditions it may put you at greater risk for developing SIBO. Part of successful treatment of SIBO is identifying the root cause so it can also be treated to prevent relapse.

Bottom Line

I can't re-iterate this enough, but please do not diagnose yourself with SIBO or start yourself on any SIBO protocol without the help of an experienced healthcare practitioner! Some of these diets are extremely restrictive and it can be very difficult or even dangerous to attempt to meet your nutritional needs on them. In addition, messing around with the microbiome is not for the inexperienced. It takes skill and knowledge to choose the right protocol.

If you have a lot of symptoms despite your dietary restrictions, failed all FODMAP reintroductions, or become very bloated within minutes of eating, it may be time to discuss SIBO with your healthcare provider!