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A Comprehensive Review of IBS-D: Differential Diagnosis, Specialty Testing, and Integrative Treatment Options

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A Comprehensive Review of IBS-D: Differential Diagnosis, Specialty Testing, and Integrative Treatment Options

IBS is a common condition affecting over 11% of the global population. IBS is more prevalent in females, occurring 1.5-3.0 times more often than in males. It primarily affects people under 50 years old and accounts for half of all gastroenterologist referrals. The impact of IBS extends to finances and health, causing work and social disruptions. Annually, IBS costs U.S. workers approximately $205 million in lost wages, productivity, and sick days. In the U.S., over 600,000 office and emergency room visits are attributed to IBS each year. It is important to note- less than 50% of people with IBS symptoms seek medical care, resulting in many suffering silently without the necessary support. IBS-D is a subset of IBS and involves frequent diarrhea as a common symptom. Functional medicine can provide solutions for people with IBS-D. This article will lay out what IBS-D is, the common symptoms, the possible causes, how to diagnose it, and the various treatment options for managing IBS-D.


What is IBS-D?

Irritable bowel syndrome (IBS) is a condition that affects the gastrointestinal tract. It can cause many different digestive issues. This condition is considered a Functional Gastrointestinal Disorder (FGID) or Functional Bowel Disorder (FBD). This condition is commonly associated with alterations in gut function. However, lab values may be considered normal. For example, this condition doesn’t cause changes in bowel tissue and does not increase the risk of colorectal cancer. Although lab values may be within normal ranges, people with IBS may have chronic gastrointestinal issues. In the case of IBS-D, a subcategory of IBS, diarrhea and abdominal pain are the hallmark symptoms of this subcategory.

IBS-D Symptoms?

The main symptoms of IBS-D are diarrhea with abdominal pain, including frequent loose or watery stools. In order to be considered IBS-D, the symptoms must fit the ROME IV diagnostic criteria in which the abdominal pain must be associated with two of the following symptoms related to defecation; a change in stool appearance and/or a change in stool frequency. The abdominal pain must also be present for at least three months and occur once per week. Patients with IBS-D may also experience bloating, mucous in the stool, and urgent bowel movements that feel incomplete. Patients in this category will rarely experience constipation.

What Causes IBS-D?

The causes of IBS-D are still unknown. However, it may be due to multiple factors. Some of the factors include rapid contractions of the intestine, post-infectious IBS, food sensitivities or allergies, a more sensitive gut, changes in gut bacteria, along with stress and anxiety. In some people with IBS-D, the muscles in the intestinal walls contract faster than normal. This can create pain and discomfort in the abdomen and cause loose or watery stools. In regards to post infections of IBS, IBS-D can develop after a gut infection, such as food poisoning or traveler's diarrhea. This is considered post-infectious irritable bowel syndrome (PI-IBS). The infection can cause lasting changes to the gut, such as inflammation or altered gut bacteria, which can contribute to the symptoms of IBS-D. Many of these symptoms can last for months or years after the infection.

Food sensitivities or allergies are also thought to be a cause or trigger. Some people with IBS-D may be sensitive or allergic to particular foods, like gluten or lactose. These foods can trigger symptoms like diarrhea, bloating, and abdominal pain. Patients with IBS-D may also have a more sensitive gut in which they would experience pain, discomfort, or bloating from gas or normal intestinal contractions that would not bother most people. Another plausible cause is changes in gut bacteria: recent research suggests that alterations in the type or number of bacteria living in the gut may play a role in IBS-D symptoms. While stress and anxiety may not necessarily cause IBS-D, they can worsen symptoms. Many people with IBS-D report that stress or anxiety triggers their symptoms or makes them more severe. This condition can happen to anyone however, it is more common in young females more than males or older people.

Differential Diagnosis for IBS-D

IBS-D is considered a condition that is an exclusion of other diagnoses. Therefore, understanding the differential diagnosis is essential as the diagnosis of IBS-D can only be made after ruling out all other conditions with similar symptoms along with following the ROME IV criteria.

Many conditions can cause digestive symptoms similar to IBS-D, including small intestinal bacterial overgrowth (SIBO), intestinal fungal overgrowth, celiac disease, inflammatory bowel disease (IBD), pancreatitis, mast cell activation syndrome (MCAS), lactose intolerance, endometriosis, anxiety, and hyperthyroidism. SIBO is caused by a bacterial overgrowth in the upper digestive tract, while intestinal fungal overgrowth can occur in both small and large intestines, and celiac disease is an autoimmune condition that causes an immune response after exposure to gluten. Inflammatory bowel disease encompasses Crohn's disease, ulcerative colitis, and microscopic colitis, and can cause chronic inflammation of the gastrointestinal tract. Pancreatitis is characterized by upper abdominal pain, and mast cell activation syndrome can cause allergy-type symptoms. Lactose intolerance develops due to a deficiency in lactase, and endometriosis occurs when endometrial tissue grows outside of the uterus, causing pain and bowel movement changes. Anxiety is another condition to consider ruling out as anxiety is a risk factor for developing IBS-D and 40% of IBS patients have anxiety. Hyperthyroidism can also cause symptoms similar to IBS, such as frequent, loose bowel movements, and abdominal pain. Properly diagnosing IBS-D and ensuring effective treatment and management requires ruling out other similar conditions.

Functional Medicine Labs to Test for Root Cause of IBS-D

The diagnosis of IBS-D is completed utilizing the ROME IV criteria, as well as ruling out other conditions with similar symptoms, along with a thorough history and physical exam. Although there isn’t a specific test to diagnose IBS-D, functional medicine labs can help rule out or confirm the diagnosis. These labs can also be beneficial in assessing for underlying factors associated with the symptoms of IBS-D and aid in creating individualized treatment protocols. Here are some functional labs to consider:

SIBO Breath Test

SIBO (small intestinal bacterial overgrowth) has been shown to be indicated in 80% of IBS patients and has similar digestive symptoms as IBS-D, including abdominal pain and diarrhea. The SIBO breath test by Geneva Diagnostics can measure different gas levels associated with SIBO.

Complete Blood Count (CBC)

This blood panel measures levels of white blood cells, which can help assess for signs of infections. A CBC can be beneficial to assess for possible gut infections that may lead to post-infectious IBS.

Thyroid Panel

As hyperthyroid is a differential diagnosis, it is important to complete a thyroid panel to measure thyroid levels to assess thyroid imbalances that may be contributing to symptoms of IBS-D.

Pancreatic Function

It is important to rule out pancreatitis for IBS-D. Pancreatic enzymes (amylase and lipase) and elastase are makers that can be helpful to assess pancreatitis.

MCAS Evaluation

MCAS can cause many symptoms, including those in the gut, brain, and heart. The gut symptoms of MCAS are similar to those of IBS, such as abdominal pain, diarrhea, and bloating. Tryptase and histamine are reliable markers to gain information on mast cell function.

Lactose Malabsorption Breath Test

Lactose maldigestion can lead to symptoms like abdominal pain, diarrhea, gas, and bloating after consuming foods that contain lactose. The intensity of these symptoms is influenced by the quantity of lactose consumed and the severity of lactase deficiency. This test is used to help diagnose lactose malabsorption. This condition can be relevant to those experiencing IBS-D symptoms, as lactose intolerance is a differential diagnosis.

IBD and Celiac Assessment

IBD and Celiac symptoms include persistent diarrhea with abdominal pain and weight loss. Calprotectin and lactoferrin are intestinal inflammatory markers often elevated in active IBD and celiac disease.

Comprehensive Stool Test

Intestinal fungal overgrowth, often associated with candida, can cause initial generalized symptoms of IBS-D, such as bloating, pain, and diarrhea. In order to rule it out, a comprehensive stool test will test for intestinal fungal overgrowth, such as candida overgrowth.

Gut Zoomer

The Gut Zoomer test analyzes the gut microbiome to assess overall gut health. It detects pathogens in the gastrointestinal system that may cause chronic diseases such as intestinal fungal overgrowth. Intestinal fungal overgrowth, often associated with candida, can cause initial generalized symptoms of IBS-D, such as bloating, pain, and diarrhea. This test identifies three types of dysbiosis that may lead to conditions such as IBS.

Food Sensitivity Testing

Some people with IBS-D may be sensitive or allergic to certain foods, like gluten or lactose. A food sensitivity or food allergy test can help determine if these foods may be possible triggers for IBS-D.

Other Lab Test to Check

Some other labs to consider involve imaging studies to help rule out other conditions of IBS-D. For example, imaging studies such as ultrasound, MRI, and CT scans can be helpful in detecting endometriosis if this condition is considered a differential. For other conditions such as IBD, colonoscopies are used to directly visualize and biopsy the small and large intestines, which is necessary to diagnose celiac disease and IBD definitively. Abdominal and/or endoscopic ultrasound and endoscopic retrograde cholangiopancreatography (ERCP) are used to assess the pancreas. It's important to consult your healthcare provider to decide which tests may be appropriate based on individual symptoms and medical history.


Conventional Treatment for IBS-D

Treatments for IBS-D can involve both conventional and integrative approaches, such as lifestyle modifications, dietary changes, and clinically relevant supplements, to manage the symptoms and address some of the underlying factors.

Conventionally treatments typically involve medications. In some people with IBS-D, the muscles in the intestinal walls contract faster than normal. This can cause abdominal pain and lead to loose or watery stools. This is why medications that slow down intestinal contractions, like antispasmodics, are sometimes used to treat IBS-D. Antispasmodics are medicines that relax the muscles in the intestines. They can help reduce pain, bloating, and the urge to use the bathroom. Other medications include anti-diarrheal products like loperamide can also decrease diarrhea by slowing down gut contractions and allowing more time for water absorption. If those treatments don’t work, then antibiotics such as Rifaximin and pain-blocking medications may be considered.

Integrative Medicine Treatment Protocol for IBS-D

IBS-D can vary from person to person, and not everyone with IBS-D will have the same contributing factors. Understanding what triggers IBS-D symptoms for each individual can be helpful in managing this condition.

Functional medicine is a holistic approach that aims to identify underlying factors that contribute to symptoms of IBS-D while improving overall health. This approach can include making dietary changes, taking clinically relevant supplements, and other integrative approaches like managing stress. Functional medicine practitioners personalize these approaches to fit the individual needs of each patient. To assess progress and adjust the treatment plan as needed, it is important to have regular follow-ups and communicate with your practitioner.

Therapeutic Diet and Nutrition Considerations for IBS-D

To help with IBS-D symptoms, dietary changes can be beneficial. Certain foods can cause symptoms like diarrhea, bloating, and pain, but can vary from person to person. Some known foods can cause food sensitivities in IBS-D such as lactose or gluten. Avoiding these foods can help improve some of the symptoms.

For others, it's harder to figure out which foods are causing the symptoms. In these cases, a low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) or a diet low in fructose (a sugar found in most fruits) can help. FODMAPs are different types of carbohydrates that can be difficult for some people to digest. They can cause symptoms such as bloating, gas, abdominal pain, and diarrhea. These carbohydrates can be found in many common foods, including fruits, vegetables, and dairy products. The low FODMAP diet focuses on restricting foods high in FODMAPs to help manage these symptoms. It’s important to note- this plan is not meant to be permanent but is rather implemented in phases. During the elimination phase, high FODMAP foods are avoided for a short period of two to six weeks. This gives the digestive system a period of rest and allows time for symptoms to improve. After the elimination phase, FODMAP-containing foods are gradually reintroduced to identify which ones trigger symptoms.

Supplements That Help With IBS-D Symptoms

Functional medicine treatment for IBS-D incorporates clinically relevant supplements that have anti-inflammatory and gut-supporting properties. Here are some of the supplements used in treating IBS-D and how they may help:


Fiber supplements are commonly used to improve IBS symptoms by enhancing the texture of stools, promoting the growth of beneficial bacteria, and reducing pain signals through interactions with the nervous system. Non-fermentable fibers like psyllium, oats, and partially hydrolyzed guar gum are generally well-tolerated by individuals with IBS. The recommended daily dose is 25 grams.


Curcumin comes from turmeric, which has potent anti-inflammatory effects that can help alleviate abdominal pain. There isn’t a specific dosing protocol for IBS at this time. However, there is a dosing recommendation for digestive issues such as peptic ulcers, which is 600 mg per day for 4 weeks.

Boswellia Serrata

Boswellia serrata is an herb from India that has been used in traditional medicine. Its resin contains boswellic acid, which is believed to have beneficial effects on gut inflammation. The dosing recommendation for IBS is 250 mg per day for adults for 1-6 months.


Probiotics can also help reduce gut problems and prevent inflammation from happening by decreasing the number of lipopolysaccharides (LPSs) that activate immune cells. When these immune cells are activated, they can cause inflammation throughout the body. Probiotics have been shown helpful in gut inflammatory conditions such as IBD, celiac, and IBS. Supplements can vary in dosages and strains. The recommended dose for IBS is 2-8 billion CFU, total probiotics per day for a minimum of 3 months.

STW5 (IberogastⓇ)

STW5 is a herbal remedy that has been found both safe and effective in treating functional gastrointestinal disorders, such as IBS. This formula contains alcoholic extracts of Iberis amara totalis recens, angelicae radix, cardui mariae fructus, chelidonii herba, liquiritiae radix, matricariae flos (chamomile), melissae folium (lemon balm), carvi fructus and menthae piperitae folium (peppermint). The beneficial effects of this formula are believed to be due to its ability to relax muscle spasms and reduce inflammation in the digestive system, resulting in relief from symptoms.


Supplementation with pectin was shown to improve symptoms of IBS-D such as diarrhea and stool frequency. It also helped to improve the fecal bacteria composition. The recommended dose is 24 grams per day for a minimum of 6 weeks.


Anti-microbial herbs have also been shown to help balance the microbiome and improve IBS symptoms. Lemon balm has anti-anxiety and antidepressant effects, which may benefit IBS patients. Coptis root has shown inhibitory effects on human bacteria. Indian Barberry root extract, containing berberine, possesses antimicrobial, anti-inflammatory, and antidiarrheal properties. Equisetum arvense L. demonstrates strong antimicrobial activity against various enteric microorganisms and fungi. Thymus vulgaris exhibits potent antimicrobial and anti-inflammatory actions.

Peppermint Oil

Peppermint oil should be taken as an enteric-coated supplement and has been shown to have antispasmodic effects that relax the muscles of the intestines. They can help reduce pain, bloating, and the urge to use the bathroom urgently.

When to Retest Labs

Functional medicine labs can help identify imbalances and underlying factors associated with the symptoms of IBS-D. However, the process of functional medicine can take time and often require ongoing monitoring and retesting to track progress. The frequency of retesting will vary depending on the individual case and the specific labs that were ordered. In general, it's recommended that labs be retested at regular intervals, usually, every 3 to 9 months, to track progress and make sure that the treatment plan is having the desired effect. The specific frequency of retesting will be determined by the functional medicine provider based on an individual's needs and response to treatment. This process is usually collaborative with the patient to ensure that testing isn’t being completed excessively while ensuring clinical relevancy and progress.



IBS-D is a chronic gastrointestinal condition that can cause abdominal pain and diarrhea, amongst other symptoms. There is no specific test to diagnose IBS-D and it is considered a diagnosis of exclusion, meaning other conditions should be ruled out. Therefore, this condition can be difficult to manage and treat. Functional medicine approaches such as the FODMAP diet and anti-spasmodic supplements can be useful in managing IBS-D symptoms. These integrative approaches can help improve the quality of life for those living with IBS-D. Functional medicine practitioners can assess your individual condition and create a personalized treatment plan.

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
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