Irritable Bowel Syndrome: Mark Pimentel, MD

Irritable bowel syndrome (IBS) is the most common gastrointestinal disorder, affecting 10-15% of the world’s population. Approximately two-thirds of those who suffer from IBS are women. The disease can have mild forms or cause severe debilitation as diarrhea alternates with constipation. Severe cramping and bloating also are common. Because chronic IBS is so debilitating, it often disrupts the daily lives of people with this disorder.

April is IBS Awareness Month, so we recently spoke with Mark Pimentel, MD, about the primary cause of IBS, a definitive test for the disease and ways to manage the chronic illness. Pimentel is an associate professor of gastroenterology and executive director of the Medically Associated Science and Technology program at Cedars-Sinai. He led the research initiative to develop the first diagnostic blood test for IBS.

Newsroom: What do we know now about the cause of irritable bowel syndrome (IBS)?
Pimentel: In the past, irritable bowel syndrome was often thought to originate in your head; the symptoms were thought to be brought on by stress or by psychological issues like anxiety and depression. In the beginning, patients suffering from chronic abdominal pain and diarrhea or constipation don’t know they could have IBS, so they often embark on a long and expensive journey seeing specialists and taking medical tests. Trying to get a diagnosis involves physicians testing for, and then eliminating, this disorder or that one. It is not uncommon for me to see a patient who's had to spend up to $20,000 out of pocket trying to pinpoint why they are ill.

Newsroom: Is there a specific test for IBS?
Pimentel: We now know for certain that food poisoning can trigger and lead to a cascade of events in the gut that result in irritable bowel syndrome. Toxins produced by bacteria, such as salmonella, can severely harm the digestive system by damaging nerves critical to healthy gut function. The IBS blood test developed here at Cedars-Sinai identifies the presence and amount of two specific antibodies reacting to those toxins. Understanding that has helped us develop diagnostic tests and identify new therapies.

Figuring out the link between the disease and episodes of acute gastroenteritis (food poisoning) has enabled us to keep refining the accuracy and specificity of the test. If the blood test is positive, there’s a 90% likelihood the patient has irritable bowel syndrome, called IBS-D if it includes diarrhea, or IBS-M, which is a mixed illness that can include constipation as well.

Newsroom: How is IBS treated? Can it be cured?
Pimentel: One of the drugs that we identified is the antibiotic rifaximin, which the Food and Drug Administration approved for treatment of IBS-D. It reduces the buildup of bacteria in the small bowel, caused by food poisoning. It can work for some people for a long period of time; one course of treatment and a patient can have a year or two of benefit. But it generally comes back, so we treat it again with good results for many patients who report feeling 90% better. While you are feeling better, it may seem your disease is cured, and that certainly is a good thing. But we are still a way away from a true “one and done” cure. Our research is robust, with the aim of identifying a cure, as we investigate more treatment options.

Newsroom: What role does diet play in managing IBS?
Pimentel: Diet can be important in the management of the symptoms of irritable bowel syndrome. There are three diets that seem to help patients, but they are all restrictive with upsides and downsides for good health. Keep in mind that the diets are not meant to be a permanent way of eating to manage symptoms. The food eliminations are meant to be tried for three months or so to see if you get relief. Each diet has some nutritional deficits.

In the early 2000s, we thought if we restrict calories to the bacteria building up in the gut following food poisoning, we could starve them out with selective eating, but not starve the patient. Three diets that seem to help patients manage the symptoms of IBS are the elemental diet, the low fermentation diet, and the new kid on the block, the low-FODMAP diet.

• Elemental Diet: An elemental diet is made up of easily digestible formulas that come in liquid or powder form and provide all the nutrients your body needs, such as protein and amino acids. Food is stripped down to its essential elements and you mix that powder with liquid to make a shake. There is no solid food on this diet.
• Low Fermentation Diet: This is a somewhat restrictive eating plan that allows patients to consume easily digested starches and sugars. It limits fermentable carbohydrates that can feed bacteria. Patients need to reduce fiber, fructose, the natural sugar found in fruit, as well as lactose, the sugar in milk. Meat and fish and other sources of protein are allowed and so are easy-to-digest carbohydrates including rice, potatoes, and sweet potatoes.
• Low-FODMAP Diet: This diet works to eliminate foods that tend to ferment in your small intestine and feed bad bacteria. It stands for Fermentable Oligo-Di and Mono saccharides And Polyols. These are four kinds of sugar naturally present in hundreds of foods, from onions and apples to mushrooms and cheese. This diet is designed to drastically reduce your exposure to these sugars that can trigger symptoms in people with severe digestive issues like IBS. But while patients are trying to starve out bad bacteria in the gut by adhering to low-FODMAP eating, they also risk developing some nutritional deficits if they do the diet longer than 90 days.

Also, with a low-FODMAP diet you start to see the gut microbiome disrupted. And because you're starving everything for so long, you're also potentially changing the microbiome in a negative way by reducing the diversity and balance of trillions of bacteria that help maintain good health. The elemental diet should only be tried for about two weeks to try and knock down the bad bacteria levels in the gut. It is difficult to sustain for a long period of time, according to patient reports.

While we do not see any of these diets as a long-term strategy, I think the low fermentation diet might be most sustainable and is a more varied diet, nutritionally.

Newsroom: Are you encouraged about the help available to IBS patients?
Pimentel: While we can't cure all cases of IBS, we're doing so much better than we were 20 years ago. I've had patients come to me and say, “Dr. Pimentel, I am feeling better, I'm 50% better.” I look at them and say my goal is 80%. For most patients, we get there, and they're surprised that we can get there now. I think that’s a positive, encouraging sign.

Read More on the Cedars-Sinai Blog: Healthy Bowel Movements: Why You Should Pay Attention to Your Poop