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Irritable Bowel Syndrome (IBS) is the most common functional gastrointestinal disorder worldwide, with prevalence rates ranging from 9 to 23 percent depending on location. IBS affects approximately 15 percent of Americans and is the second leading cause of missed work (behind only the common cold). It accounts for 12 percent of visits to primary care providers and an estimated $21 billion annually in direct medical expenses and indirect costs associated with decreased productivity and absenteeism.

The symptoms of IBS include gas, bloating, constipation, diarrhea, alternating constipation and diarrhea, and abdominal pain. They can range from mildly annoying to completely debilitating.

But what is IBS? In medical terms, it’s a “diagnosis of exclusion.” This means that it’s a label applied when other disease conditions are ruled out. If you go to your doctor complaining of gas, bloating, and pain, she may run a number of tests to determine if you have inflammatory bowel disease (IBD), GERD, diverticulitis, and other problems that affect the structure of the intestines.

If these structural conditions are ruled out, the doctor will evaluate your symptoms based on the Rome Criteria, a set of guidelines developed by consensus to diagnose IBS. These include:

Recurrent abdominal pain or discomfort at least three days per month in the last three months associated with two or more of the following:

  • Improvement with defecation
  • Onset associated with a change in stool frequency
  • Onset associated with a change in stool consistency

If you meet these criteria, you will be diagnosed with IBS. Your doctor will then likely prescribe any of the following medications, as dictated by your symptoms:

  • Anti-diarrheal medications. These include OTC drugs like loperamide or bile acid binders like cholestyramine or colesevelam. (Ironically, many of these medications cause bloating as a side effect!)
  • Anticholinergic or antispasmodic medications. These include hyoscyamine and dicyclomine and are used to reduce bowel spasms and pain. (Unfortunately, they worsen constipation and can lead to other symptoms like difficult urination. They also increase the risk of SIBO, which is an underlying cause of IBS—see below.)
  • Doctors will often prescribe SSRIs to people with IBS because they help relieve depression (associated with IBS) as well as inhibit the activity of neurons that control the intestines.
  • Specific medications for IBS. These include alosetron, which is designed to slow intestinal motility and reduce diarrhea, and lubiprostone, which increases fluid secretion in the intestine and speeds up motility. These drugs are typically used as a last resort, and alosetron can only be prescribed by doctors enrolled in a special program because it has previously been removed from the market due to side effects and risks.

What’s wrong with the conventional treatment for IBS?

The fundamental problem with the conventional approach to IBS is that it merely suppresses symptoms and doesn’t address the underlying causes. Look at the list of medications above. They are aimed primarily at slowing or increasing intestinal motility (to reduce diarrhea or constipation) and relieving pain.

Even if these medications are effective for those purposes (which they often aren’t, according to many IBS sufferers), they often have side effects that are identical to symptoms that people with IBS already experience—such as gas and bloating. And in some cases, the drugs have more serious complications and risks. Alosetron, a medication used to treat severe diarrhea-predominant IBS, was temporarilywithdrawn from the market by GlaxoWellcome after the occurrence of serious life-threatening adverse effects, including five deaths and additional bowel surgeries.

A better approach to IBS: treat the underlying cause!

Given the failure of the conventional approach to successfully treat IBS, and the side effects and risks associated with drug treatment, patients deserve another alternative.

Fortunately, IBS can be successfully treated—and even cured—using functional medicine. In functional medicine, we focus on addressing the underlying cause of health problems rather than just suppressing symptoms. This leads to lasting improvement and genuine healing.

But what are the underlying causes of IBS? The answer depends on the individual patient. IBS is not a single disease with a single cause. Rather, it’s a syndrome—a collection of signs and symptoms—that has multiple possible causes.

That said, both the scientific research and my clinical experience suggest that the following five pathologies are the underlying cause of IBS in most cases.

Traditionally, IBS has been considered a “functional” gastrointestinal disorder. This means that it is caused by abnormal function of the GI tract, rather than structural or biochemical abnormalities. As you’ll see below, that may be true in some cases, but in others there is very likely a biochemical abnormality present (such as bacterial overgrowth).

This is crucial to understand, because for many years patients with IBS were told that it was “all in their head.” The implication was that IBS is a psychosomatic disorder caused by anxiety, depression, or some unknown psychological problem.

While IBS may involve a dysfunction in the gut–brain axis, we now know that it is primarily caused by distinct biochemical and even structural changes in the GI tract. This important discovery has removed the painful (and unwarranted) stigma from the IBS diagnoses and offers hope to the hundreds of millions of IBS sufferers around the world.

#1: Small intestine bacterial overgrowth (SIBO)

SIBO is a condition characterized by abnormal overgrowth of bacteria in the small intestine. One study reported that up to 84 percent of IBS patients have SIBO and that patients with IBS were 26 times more likely to have SIBO than controls. (1)

Results from subsequent studies examining the association between SIBO and IBS were mixed. This is in part because there is currently no consistently accepted, gold-standard method of testing for SIBO, and the techniques varied from study to study.

However, there is other evidence to support the idea that SIBO plays a causal role in IBS for at least some patients. Antibiotics that are used to treat SIBO—such as rifaximin and neomycin—have been shown to be effective for treating IBS. For example, in one randomized controlled trial (RCT), treatment with rifaximin for 10 days resulted in symptom improvement that lasted for up to 10 weeks in IBS patients. (2) A recent meta-analysis of five studies found rifaximin to be effective for global IBS symptom improvement and more likely to reduce bloating than a placebo. (3)

#2: Disrupted gut microbiota (aka “dysbiosis”)

The human gut microbiota is a complex community of over 100 trillion microorganisms that influence physiology, metabolism, nutrition, and immune function. Disruption of the gut microbiota has been linked with GI conditions like inflammatory bowel disease as well as a wide range of extra-intestinal inflammatory conditions like diabetes and obesity.

Studies have shown that up to 83 percent of patients with IBS have abnormal fecal biomarkers, and 73 percent have intestinal dysbiosis (i.e., a disrupted gut microbiome). (4)

Numerous studies have also found that both prebiotics and probiotics, which modulate the gut microbiota, can be effective for treating IBS. (5) In addition, the low FODMAP diet, which restricts certain carbohydrates that feed intestinal bacteria, has been shown to benefit IBS patients. (6)

#3: Increased intestinal barrier permeability (aka “leaky gut”)

One of the primary roles of the gastrointestinal tract is to serve as a barrier system that prevents pathogens, undigested food particles, and other undesirable substances from entering the body.

IBS has been associated with increased permeability of the intestinal barrier in several studies, which may be modulated by a cytokine called interleukin-22 (IL-22) that is known to play a role in regulating gut permeability. (7, 8) Note that this is a structural change to the gut, which would suggest that IBS is not always a functional disorder.

#4: Gut infections

The human gut is naturally resistant to infection by pathogenic bacteria, thanks to acid produced in the stomach that is designed to kill potential invaders. However, many aspects of the modern diet lifestyle—such as chronic stress, poor diet, and use of acid-suppressing drugs—have compromised this defense system.

A number of gut infections have been linked to IBS. For example, food poisoning caused by Campylobacter bacteria leads to chronic, persistent IBS in as many as 10 percent of cases. (9) Intestinal parasites like Blastocystis hominis, Dientamoebafragilis, and Giardia lamblia may be relatively common—yet often undiagnosed—causes of IBS, even in the developed world. (10)

#5: Non-Celiac Gluten Sensitivity and other food intolerances

Non-Celiac Gluten Sensitivity (NCGS) is a reaction to gluten that is not autoimmune (celiac disease) or allergic (wheat allergy). Despite claims to the contrary in the popular media, NCGS is a legitimate and potentially serious condition. In fact, Irecently argued that it may be a greater public health challenge than celiac disease itself.

NCGS patients usually present with symptoms such as gas, bloating, abdominal pain, and changes in stool frequency and consistency that are indistinguishable from IBS. They also often present with extra-intestinal symptoms like “brain fog” and fatigue, which are common among IBS sufferers.

Intolerances to other foods like dairy products, eggs, peanuts, and seafood are also common among IBS sufferers. These may be true food allergies (IgE-mediated) or more mild intolerances (IgG- or IgA-mediated).

One recent, large review of 73 individual studies concluded that food allergy and intolerance—including reactions to wheat and gluten—should be considered as a potential underlying pathology for IBS. (11)

In my own clinical experience, I’ve found that both gluten/wheat sensitivity and other food intolerances are extremely common contributing factors to IBS. It’s worth pointing out that, in many cases, food intolerances are themselves caused by some of the other pathologies we’ve already discussed in this article. Put another way, both IBS and food intolerances are symptoms of deeper causes like SIBO and gut infections.

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