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Top 5 Functional Medicine Labs for IBS-C Patients

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Top 5 Functional Medicine Labs for IBS-C Patients

Functional gastrointestinal disorders (FGID) affect more than 40% of people worldwide, significantly impacting the quality of life and healthcare-associated costs. Irritable bowel syndrome (IBS) is one type of FGID caused by changes in the neuromuscular physiology of the bowels, causing disruptive digestive symptoms. IBS is estimated to affect 10-15% of people in the United States and is twice as common in women than in men.

Many doctors say that IBS is incurable. Conventional treatment recommendations state that IBS treatment goals include symptom relief to improve quality of life (1). Practitioners trained in functional medicine will disagree. Thorough history taking and specialty testing help functional medicine providers to expose imbalances leading to altered bowel habits and digestive symptoms, helping to customize effective solutions for the individual. This article will discuss five key specialty tests that doctors should consider when working with patients with IBS-Constipation.


What is Irritable Bowel Syndrome-Constipation?

IBS is a diagnosis based on gastrointestinal (GI) symptoms and altered GI function. It is clinically diagnosed using ROME IV criteria when all other GI pathology has been ruled out. IBS is characterized by abdominal pain that occurs at least once weekly for at least three months and is associated with at least two of the following: related to defecation, a change in stool frequency, and a change in stool appearance.

IBS, once diagnosed, can further be categorized by predominant stool type. IBS-Constipation (IBS-C) is diagnosed when more than one-quarter of abnormal bowel movements are hard and lumpy (constipated), and fewer than one-quarter are loose in consistency (diarrhea). 

Other IBS subtypes, not to be discussed in this article, include IBS-diarrhea (IBS-D) and IBS-mixed (IBS-M).

How is IBS-C Different from Irritable Bowel Syndrome?

IBS-C isn't different from IBS; rather, it is a more specific classification of IBS that specifies constipation as the predominant experienced stool type (over diarrhea or an equal mix of diarrhea and constipation).

IBS-C Symptoms

The hallmark symptoms of IBS-C are abdominal pain/discomfort and constipation. Constipation can be defined by the frequency and consistency of bowel movements. Patients who are constipated can experience stools that are hard and dry, painful or difficult to pass, and are incomplete. Constipation can also be defined as having fewer than three bowel movements weekly. (2)

Additional symptoms that patients may experience with IBS-C include (2):

  • Bloating
  • Flatulence
  • Abdominal discomfort improved after a bowel movement
  • Mucus in the stool 

Symptoms that would indicate a more severe pathology and warrant immediate medical evaluation include:

  • Weight loss
  • Rectal bleeding
  • Iron deficiency anemia (IDA)
  • Vomiting
  • Constant pain, not relieved by passing gas or bowel movement 

Causes of IBS-C

Factors that may increase your risk but do not guarantee the development of IBS-C include age under 50, female sex, estrogen therapy, and family history of IBS.

Immune Activation

Increasing evidence suggests the role of immune activation in the origin of IBS, especially regarding post-infectious IBS (PI-IBS). PI-IBS is the onset and persistence of IBS symptoms after an acute GI infection, despite eradicating the inciting pathogen. 5-32% of intestinal infections lead to PI-IBS. Chronic intestinal inflammation with mucosal infiltration of T-lymphocytes and mast cells and increased production of proinflammatory cytokines have been documented as characteristic histological features of PI-IBS. (2, 3)

Chronic psychological stress has been reported as a factor in inducing immune activation, causing low-grade chronic inflammation and worsening physical symptoms. A sustained elevation of cortisol associated with the biological stress response is associated with worse GI symptoms in patients with IBS. (2, 4)

Adverse food reactions are abnormal reactions to the ingestion of a particular food. Food hypersensitivities are a type of immune-mediated adverse food reaction in which IgE, IgA, and/or IgG antibodies can be measured in response to the food trigger, depending on the type of hypersensitivity (food allergy vs. food sensitivity).


Dysbiosis is common in IBS patients. Characteristic dysbiotic patterns in IBS patients include lower fecal levels of Lactobacillus spp. and Bifidobacterium spp. and higher levels of E. coli and Enterobacter spp. compared to healthy controls. An additional study found elevated fecal Veillonella spp. levels in patients with IBS-C.

Methanobrevibacter smithii is an archaeon and the predominant methane-gas producer in the GI tract. Intestinal methanogen overgrowth (IMO), diagnosed by elevations of methane gas levels on breath testing, has been linked to IBS-C.

Serotonin Dysregulation

Enterochromaffin cells in the gut synthesize 95% of the body's serotonin and release serotonin (5-HT) in response to mechanical and chemical stimulation. Enterochromaffin cells and serotonin, through their actions on 5-HT receptors, play a significant role in the control of GI motility, sensation, and secretions. Reductions in plasma 5-HT concentrations in patients with IBS-C support the hypothesis that serotonin dysregulation contributes to IBS-C. (2)

Top 5 Functional Medicine Labs to Test for Root Cause of IBS-C

Functional medicine practitioners utilize specific labs to further evaluate the root causes of IBS-C. Below are some of the most commonly run functional labs:

Comprehensive Stool Test

A comprehensive stool test collected at home by the patient over 1-3 days analyzes biomarkers commonly abnormal in patients with IBS-C. Comprehensive stool tests measure biomarkers that can be divided into the following categories:

  • Pathogenic and opportunistic infections: through PCR and culture methods, bacterial, viral, fungal, and parasitic infections can be identified
  • Microbiome assessment: identification and quantification of the commensal gut bacteria to assess for dysbiosis, unavailable through standard labs
  • Microbiome metabolites: imbalances in short-chain fatty acids and beta-glucuronidase produced by commensal bacteria can indicate dysbiosis and can alter gut function
  • Digestive markers: maldigestion and malabsorption can alter intestinal motility and result in abdominal pain, gas, bloating, and abnormal bowel movements
  • Inflammatory markers: the presence and level of intestinal inflammation can result from malabsorption, dysbiosis, infection, or a more severe GI pathology 

Allopathic doctors do not usually order many of the biomarkers measured on a comprehensive stool test. Even subtle imbalances in the microbiome, digestion, and immune system can lead to unfavorable variations in gut function, contributing to IBS-C.

SIBO Breath Test

A breath test can diagnose small intestinal bacterial overgrowth (SIBO) and IMO. A 3-hour breath test is preferred for patients with constipation and slowed intestinal motility. It also assesses for IMO present in the large intestine.

Food Sensitivities

Food allergies and sensitivities can trigger immune-mediated responses and inflammatory symptoms. A blood panel that measures IgE, IgG, and IgG4 antibodies can diagnose adverse food reactions contributing to immune activation related to IBS pathology.


An adrenal stress panel measures salivary cortisol at multiple time points throughout the day. Deviations in the typical cortisol secretion pattern can indicate maladaptation to chronic stress.


Abnormalities in neurotransmitters can also result from chronic stress. Functional providers typically measure neurotransmitters through urine, but serotonin can also be measured through a blood sample.

Additional Labs to Test for IBS-C 

A basic blood panel consisting of thyroid hormones, a CBC, and a CMP is beneficial in the initial evaluation of IBS-C. These tests often come back normal but are helpful in screening for and ruling out hypothyroidism, infection, and liver/gallbladder pathologies that can contribute to digestive symptoms.

Functional Medicine Treatment for IBS-C

Functional medicine practitioners create thorough treatment plans to help resolve the uncomfortable symptoms of IBS-C. Below are evidence-based treatment options:

Diet for IBS-C

Healthy eating habits can support digestive function and provide IBS symptom relief. Eat regular meals spaced throughout the day at a slower pace. Eat according to your hunger cues: eat when you are hungry, and stop eating when you are full. Drink at least 8 cups of water daily and limit coffee intake to no more than 2 cups daily. Reduce intake of alcoholic, carbonated, and sugary drinks. (5)

Therapeutic elimination diets can help manage IBS-C symptoms. One study found that an elimination diet based on the results of IgG food testing resulted in a 26% reduction of IBS symptoms after 12 weeks. 

Certain foods that commonly exacerbate IBS symptoms and can improve symptoms when eliminated include greasy and fried foods, sorbitol or fructose, and legumes. (5)

A dietary fiber intake of 25-30 grams daily is a long-standing recommendation for IBS. Fiber supplementation can result in mixed results in patients with IBS; soluble fibers generally provide superior results over insoluble fibers. (5)

Is the Low FODMAP Diet Beneficial for IBS-C patients?

The low FODMAP diet is intended to eliminate certain carbohydrates from the diet. FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. Organisms ferment FODMAPs in the small and large intestines; this process produces gas and draws water into the intestines, commonly causing IBS-like symptoms. Research indicates that following a low FODMAP diet can improve GI symptoms (e.g., abdominal pain, bloating, constipation, diarrhea, and flatulence) in 86% of patients with IBS. The low FODMAP diet may particularly benefit patients with SIBO, IMO, or other forms of bacterial dysbiosis. (5

What are the Best Supplements for IBS-C?

Herbal antimicrobials often recommended for treating SIBO, dysbiosis, and other GI infections include berberine, oregano, thyme, and wormwood. Herbal antimicrobials are just as effective as prescription antibiotics in treating SIBO.

Proven beneficial effects of probiotics include improved stool consistency, abdominal symptoms, and quality of life. Research has concluded that various strains and doses of probiotic mixtures can benefit digestive function. Comprehensive stool test results can guide treatment recommendations for the type and dosage of probiotics.

Carminative herbs, such as fennel and peppermint, soothe the gut wall and regulate intestinal contractions to ease abdominal pain and remove excess gas from the digestive tract. 

Gingerol, the principal constituent of ginger root, acts as a prokinetic in the stomach and small intestine, enhancing GI motility. Prokinetic agents can symptomatically relieve digestive symptoms like gas, bloating, and abdominal pain. Additionally, they are commonly implemented in treatment and prevention protocols for SIBO and IMO.

Nervines and anxiolytic herbs can calm the nervous system and regulate the stress response in chronic stress and anxiety. Valerian root, kava root, and passionflower are three options that have evidence to support their efficacy in managing anxiety. (6, 7)

People with IBS-C have been shown to have lower levels of butyrate, a type of short-chain fatty acid, than healthy controls. Butyrate supplementation for 4-12 weeks improved abdominal pain and bowel habits in patients with IBS.


IBS-C is a subtype of irritable bowel syndrome characterized by chronic abdominal pain and constipation. IBS is common and causes significant disruption to daily living and quality of life. Conventional treatment options often fail to provide long-term, lasting resolution of symptoms. A functional medicine approach to treating IBS-C utilizes evidence-based dietary modifications, botanical medicine, and nutritional supplements to target underlying imbalances contributing to gastrointestinal dysfunction and resolve IBS symptoms.

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1. Wilkins, T., Pepitone, C., Alex, B.K., et al. (2012). Diagnosis and management of IBS in adults. American Family Physician, 86(5), 419–426.

2. Saha, L. (2014). Irritable bowel syndrome: Pathogenesis, diagnosis, treatment, and evidence-based medicine. World Journal of Gastroenterology, 20(22), 6759.

3. Thabane, M., & Marshall, J. (2009). Post-infectious irritable bowel syndrome. World Journal of Gastroenterology, 15(29), 3591.

4. Morey, J.R., Boggero, I.A., Scott, A., et al. (2015). Current directions in stress and human immune function. Current Opinion in Psychology, 5, 13–17.

5. IFFGD. (2022b, October 18). IBS Diet. International Foundation for Gastrointestinal Disorders.

6. Shinjyo, N., Waddell, G., & Green, J. (2020). Valerian Root in Treating Sleep Problems and Associated Disorders—A Systematic Review and Meta-Analysis. Journal of Evidence-Based Integrative Medicine, 25, 2515690X2096732.

7. Lakhan, S.E., & Vieira, K.F. (2010). Nutritional and herbal supplements for anxiety and anxiety-related disorders: systematic review. Nutrition Journal, 9(1).

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