What Is SIBO, Exactly? An MD Weighs In

Most people have heard of irritable bowel syndrome (IBS), a common disorder that affects the stomach and intestines, causing diarrhea, constipation, and bloating. But now, a similar condition known as SIBO is getting more attention.

Recently, Selena Gomez shared that she struggles with SIBO, after body shamers criticized the "Only Murders in the Building" actress for posing with her hand in front of her torso for the premiere of her new movie "Emilia Pérez," insinuating that she was trying to hide her body. No one ever has to defend themselves or their body, but according to Elle, Gomez replied in a since-deleted comment on TikTok, explaining, "This makes me sick. I have [SIBO] in my small intestine. It flares up. I don't care that I don't look like a stick figure. I don't have that body. End of story. No I am NOT a victim. I'm just human."

SIBO is actually one of the more common digestive disorders, often associated with other pre-existing conditions like Crohn's or celiac disease. Symptoms aren't limited to just bloating, though. The condition can also cause diarrhea, nausea, indigestion, and discomfort while eating. To help break down everything you need to know about SIBO, we tapped a physician. Ahead, an MD explains SIBO symptoms, causes, and potential treatment.

Experts Featured in This Article:

Laura Purdy, MD, is a family medicine physician and founder of telehealth company Swell Medical.

What Is SIBO?

"Small intestinal bacterial overgrowth, commonly referred to as SIBO, is a condition that results from an overgrowth of bacteria in the small intestine and gut," says Laura Purdy, MD, a family medicine physician and founder of telehealth company Swell Medical. It's normal and healthy to have some bacteria living in your gut, but too many can wreak havoc on your intestines and cause problems with your digestion, ultimately leading to uncomfortable symptoms, she explains.

To break it down a bit more, bacteria in your small intestines digest carbohydrates and convert them into gas and short-chain fatty acids (fatty acids with fewer than six carbon atoms that are a byproduct of bacterial fermentation in the gut), according to the Cleveland Clinic. More bacteria can then mean more gas and other byproducts, causing you to feel gassy.

The excess bacteria also feeds on proteins and vitamin b12, per the Clinic, which can worsen the digestion of fats and lead to poor absorption of nutrients and fat-soluble vitamins. The result? Unpleasant gastrointestinal symptoms.

Symptoms of SIBO

SIBO is typically marked by the following signs and symptoms, according to Dr. Purdy. You may experience some or many of these symptoms, depending on the severity of your condition.

If left untreated, SIBO can also cause poor fat absorption, per Yale Medicine, which can lead to deficiencies in vitamin D, vitamin B12, and iron, since the excess bacteria eats all the nutrients.

What Causes SIBO?

SIBO occurs when there's an overgrowth of bacteria in the small intestine and gut, Dr. Purdy says. Your body typically maintains the balance of flora in your gut through a complex network of chemical and bodily functions, per the Cleveland Clinic, but when one or more of these functions is off kilter, SIBO may present.

Like most conditions, it's difficult to narrow down the exact offender of SIBO, but here's a few common causes.

How Is SIBO Diagnosed?

The most common and noninvasive way to diagnose SIBO is via a breath test, Dr. Purdy explains. "This test is taken after consuming a sugary solution (a mixture typically made of glucose and water) and measures the level of hydrogen and/or methane in the breath," she says. If you exhale and there's a rapid rise in your hydrogen and/or methane levels, it may be an indication that there's a bacterial overgrowth in your small intestines.

A small intestine fluid culture can also identify a bacterial overgrowth, although it is more invasive, Dr. Purdy says. To obtain the fluid sample, a healthcare provider will pass a long, flexible tube down your throat and through the upper digestive tract to your small intestine. From there, a sample of the intestinal fluid is withdrawn and tested in a lab to identify the growth of bacteria.

Additionally, your doctor may order a blood test to identify vitamin deficiencies or a stool sample to determine if there's excess undigested fat or bile acids. An X-ray, CT scan, or MRI may also be necessary to evaluate organ functioning and potential structural issues.

How Is SIBO Treated?

It may sound counterintuitive, but SIBO is commonly treated through a course of antibiotics to help reduce the bacterial overgrowth, Dr. Purdy says. Just note that antibiotics can wipe out the good and bad bacteria in your gut, so it's crucial to follow your doctor's instructions to prevent bacterial resistance, she adds.

If SIBO has caused nutritional deficiencies, a healthcare provider may prescribe oral supplementation or intramuscular injections to help fill the nutritional gap, especially if you're deficient in vitamin B12, according to the Mayo Clinic. However, you should always get approval from your doctor before starting any new supplements, since they're not FDA-approved, and therefore always carry some risk.

Finally, SIBO can sometimes be managed through a low-FODMAP diet (an eating plan that reduces certain kinds of carbohydrates that are typically hard to digest), since some carbs feed the bacteria in your gut and may worsen uncomfortable symptoms, Dr. Purdy says. Again, you should always connect with your doctor to discuss a treatment plan before making any major dietary changes.

All that said, if you have an underlying health condition that predisposes you to SIBO, it's crucial to talk with a doctor to address and treat the root cause.

Andi Breitowich is a Chicago-based freelance writer and graduate from Emory University and Northwestern University's Medill School of Journalism. Her work has appeared in PS, Women's Health, Cosmopolitan, and elsewhere.