Irritable bowel syndrome is one of the most common reasons a patient will go see a primary care physician or gastroenterologist.

The definition of IBS has changed over the years; it is now defined by a collection of symptoms and features of a patient’s history, including the onset of symptoms, and the absence of more-concerning signs, like unintentional weight loss, blood in stool, or fever. The criteria include abdominal pain and changes in bowel habits, such as diarrhea, constipation, or both. There is not a significant amount of evidence-based literature on the subject.

IBS is not a life-or-death condition. That said, it is a chronic condition that can impact a person’s quality of life and should be taken seriously by both physicians and patients.

IBS falls into a bigger category of conditions called functional gastrointestinal disorders, which are disorders involving brain-gut interactions. Though the effects are very real, they do not have structural abnormalities that doctors can typically detect on tests. Unfortunately, because of this, patients can feel dismissed, and physicians can become frustrated by an inability to identify a specific problem.

IBS can have a variety of causes—there may not be just one reason a patient is experiencing symptoms. The causes can include disruption of the normal pattern of brain-gut interactions; changes in the composition or types of bacteria present in the gastrointestinal tract; environmental factors, such as a history of infections or exposure to antibiotics; a history of breastfeeding; exposure to environmental toxins; life events or stressors; or a combination of these variables.

The most well-known forms of inflammatory bowel disease are ulcerative colitis and Crohn’s disease. IBD refers to chronic inflammation of the digestive tract: This could entail microscopic inflammation; inflammation seen on radiology tests, such as CT scans or MRIs; or inflammation that is evident to the naked eye when a gastroenterologist performs a test called an endoscopy. While IBD and IBS share a common symptom of diarrhea, other symptoms of IBD include abdominal cramps, bloody stool, fever, loss of fluids and appetite, and anemia. It is treated with specific types of medications—some of which impact the immune system—and sometimes surgery.

Small intestinal bacterial overgrowth refers to an overgrowth of bacteria in the small intestine. The way it manifests can vary from person to person, but many of the symptoms of SIBO are similar to those of IBS. Patients often experience symptoms like abdominal pain, bloating, gas, and changes in bowel habits. Most patients who have been diagnosed with SIBO have done a breath test: Deciding to do a breath test requires a careful discussion between the patient and a knowledgeable physician. The breath test measures the amount of hydrogen or methane in a patient’s breath, because bacteria can be hydrogen- or methane-producing. A positive breath test may suggest the presence of SIBO. It does not mean the patient has an infection; rather, it indicates an overgrowth of bacteria in the intestine. How a patient chooses to move forward with the information they receive from the test also requires a careful discussion with a knowledgeable physician. Some patients with SIBO may present some symptoms similar to those of IBS, but it doesn’t always mean they have IBS. If you perform a breath test on patients with IBS, most will not have SIBO.

It is extremely common. It affects both men and women and people of all ages and ethnic backgrounds. Estimates vary, but studies have suggested approximately 10 to 15 percent of the adult population in North America suffers from IBS. It also tends to be more common in women and younger patients. It is unclear why women are more likely to have IBS, but there are studies investigating this. Researchers are looking into the possible role of hormones, psychological differences, and the difference in patterns of men and women seeking care.

In terms of age, while IBS is not always present in childhood, many children who experience IBS-like symptoms will develop lingering symptoms that go into adulthood and then meet the criteria for IBS. Other times, adult patients with IBS may recall experiencing episodes of abdominal pain in their early adulthood. The development of symptoms in older patients should prompt additional testing to rule out other conditions.

There is no one genetic test or specific gene mutation for IBS, but genetics may play a role in some patients’ susceptibility to developing it. Scientists have seen clusters of functional GI disorders in families. And over the last several years, improvements in genetic analyses have enabled researchers to have a better understanding of genetic trends and variations in patients with IBS. Multiple factors likely contribute to IBS, and not every IBS patient has the same genetic profile, but with additional research, investigators may be able to identify specific genetic profiles and targets for potential medical therapies.

IBS is a clinical diagnosis based on specific criteria. It is not a diagnosis of exclusion—a doctor diagnosing an individual with IBS because they were unable to determine a specific condition. Listening to a patient’s story, evaluating their symptoms, and doing a physical examination and some limited testing may be more than enough to make the diagnosis. As patients get older, their risks of other medical problems can increase, so additional testing for patients older than fifty is often required to make sure other conditions are not responsible for the symptoms.

There are other conditions that can have similar symptoms to IBS. For example, patients with celiac disease can also experience bloating and diarrhea. But they often have other clues to the diagnosis, and some populations are more at risk for celiac disease than others. Food intolerances may be much more common than true food allergies, so a comprehensive dietary evaluation by a registered dietitian, in conjunction with a knowledgeable primary care physician or gastroenterologist, can help clarify some of these nuances. Many people also become lactose intolerant as they get older. Lactose intolerance can present symptoms similar to IBS, and usually this diagnosis can be made with a complete medical history and a trial of a lactose-free diet.

Additional tests are needed if someone has specific signs that are considered red flags in most adults. Some of these include anemia (a low blood count), osteopenia or osteoporosis (lower than expected bone density), blood in the stool, fever, and unintentional weight loss.

Triggers can vary widely depending on the patient, and a one-size-fits-all approach does not apply when it comes to IBS.

For some patients, specific food triggers may exacerbate symptoms. Dairy products do not cause IBS, but if an IBS patient is also lactose intolerant, they may experience a flare-up of more-active symptoms after consuming dairy products. Other dietary triggers for symptoms may be due to FODMAP-containing foods (fermentable oligo-, di-, and monosaccharides and polyols), which unfortunately are very common in our diets. They include frequently consumed foods such as dairy products, wheat products, beans, and fruits.

Life stressors—whether they’re positive, like a wedding, or negative, like the loss of a loved one—can also exacerbate IBS symptoms. The brain and the gut are closely connected, and the GI tract has a complex nervous system; people often refer to the gut as the second brain. We are just scratching the surface when it comes to understanding this nervous system and how it works.

Many people describe the feeling of butterflies in their stomach, gut feelings, or gut instincts, and there is scientific basis behind these sensations. They illustrate how the brain influences the different feelings in the gut. My colleagues at UCLA have been pioneers in this science, and through the use of brain imaging and laboratory studies, we continue to learn at a rapid pace.

Because there are various possible causes of IBS symptoms, its treatment requires a personalized approach. For patients with milder symptoms, treatments may be aimed at helping them deal with constipation or diarrhea. For many patients, a carefully devised plan with a physician and dietitian may involve dietary modifications that can improve a patient’s quality of life. These may include a trial of an elimination diet—a lactose-free diet or a low-FODMAP diet—which may help some patients. If SIBO is the major cause of IBS symptoms, physicians may prescribe a course of antibiotics. It is also important, though, to have a follow-up plan in case symptoms persist or recur.

In other cases, if the symptoms seem to have an overlap with a mood disorder, physicians may use medications that target the nervous system, such as ones that were originally developed to treat depression or anxiety. In these cases, the medical treatment would be different from the treatment approach for someone who primarily has dietary triggers. These medications may be effective because their mechanisms can target the brain-gut interactions that may help improve pain, discomfort, and even changes in bowel habits. There are also many nonpharmacological approaches—such as meditation, acupuncture, and cognitive behavioral therapy, to name a few—that can be promising for the right patient.

Not every physician feels comfortable managing IBS, for a few reasons: It may require multiple approaches to care, the symptoms are not always straightforward, and a comprehensive approach may be required. Patients may require regular follow-up visits, and the time constraints it places on both the patients and physicians can make access to care difficult.

As a result, a more innovative approach is beneficial. This includes the implementation of a team of specialists, such as a gastroenterologist, a registered dietitian with a gastrointestinal specialization, a gastrointestinal psychologist, and a wellness specialist, who can also use complementary techniques, such as mindfulness meditation.

At UCLA, Dr. Lin Chang and I together with our colleagues have a program like this to help the patients in our community. We hope to grow the team to help even more patients in the years to come.