Troubleshooting Tummy Woes: The Lowdown on Potential Causes for Diarrhea

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Diarrhea is a drag, to say the least. No one wants to discuss it, but everyone suffers from it at some point.

Diarrhea is defined as three or more loose or watery stools per day. In its most mild and transient form, it can be an uncomfortable nuisance, but severe or chronic diarrhea lasting two weeks or more can be dangerous, leading to dehydration, malabsorption and nutrient deficiencies.

Diarrhea is a common symptom of gastrointestinal disorders, foodborne illness and some infections and is a side effect of certain medications. Therefore, it can be difficult to pinpoint the exact cause. Get the lowdown on nine potential reasons for experiencing diarrhea.


Prevalence: 3% to 20% in the U.S. and 10% to 15% worldwide; slightly higher prevalence in women and people younger than 50; the most common functional gastrointestinal disorder in the world

Trend: Rising

Other indicators: Dull ache and/or sharp, sporadic abdominal pain; bloating; urgent defecation after eating with accompanying pain, nausea, urinary frequency, worsening menstrual symptoms, fat in stool, alternating diarrhea and constipation

Diagnostic criteria: IBS may be classified as IBS-C (constipation dominant), IBS-D (diarrhea dominant), IBS-M (mixed) and IBS-U (unspecified, meaning symptoms do not fit exactly into the other categories). IBS symptoms may alternate between classifications. The Rome IV criteria, an updated set of criteria developed as a guideline to standardize GI disorder diagnoses including IBS, specify that an IBS diagnosis can be made when someone has recurrent abdominal pain at least one day per week during the previous three months that is associated with two or more criteria (related to defecation and change in stool frequency, form or appearance). Some clinicians use the Manning Criteria, a set of symptoms with no timeframe specification. The American College of Gastroenterology does not recommend lab tests or diagnostic imaging in people younger than 50, unless accompanied by weight loss, iron deficiency anemia or family history of GI illnesses such as celiac disease, colorectal cancer or inflammatory bowel disease.

Treatment: IBS treatment is personalized and involves a combination of pharmacological treatment, psychosocial therapies and lifestyle modification such as trigger avoidance, hydration, small and frequent meals, lower-fat meals, limiting caffeine and perhaps adding probiotics. Although research is conflicting, the temporary avoidance or limiting of foods rich in specific carbohydrates called fermentable oligosaccharides, disaccharides, monosaccharides and polyols, or FODMAPs, under supervision of an RDN, may improve symptoms.

For IBS-C, gradually increasing fiber intake and pharmacological treatment are common. With IBS-D, a gradual increase in fiber intake, possible temporary FODMAP avoidance and pharmacological treatment are typical. For IBS-M, stopping use of anti-diarrheal and anti-constipation medications and a combination of treatment methods from both IBS-C and IBS-D are typical and tailored based on which symptom is most bothersome to the patient.

RDN Role: Thorough food history to determine any food avoidance issues; support and education for symptom management and lifestyle modification, possibly including low-FODMAP diet instruction


Prevalence: 1.3% of adults in the U.S.; similar prevalence between men and women with Crohn’s disease; slightly higher prevalence in men than women with ulcerative colitis

Trend: Unclear; may be plateauing in the U.S. but rising worldwide, possibly because of modernization and Westernization

Other indicators: Abdominal pain, fever, bloody stool, urgent and incomplete bowel movements, kidney stones, accompanying diagnosis of osteopenia/osteoporosis

Diagnostic criteria: Endoscopy (Crohn’s), colonoscopy (UC), imaging studies, stool samples and blood tests used to rule out other conditions

Treatment: Medications are used to decrease inflammation, modulate immune response and treat symptoms. Surgery may be required in severe cases. Treatment goals include trigger food avoidance, correcting nutritional deficiencies from malabsorption, supporting increased nutritional needs for healing and compensating for increased nutritional losses.

Possible nutritional recommendations include hydration, small and frequent meals, limiting caffeine and foods with added sugars and sugar alcohols and adding pre- and probiotic foods. Following a low-FODMAP diet also may improve symptoms. Fiber should be restricted during acute exacerbations and added back gradually when tolerated. Enteral and parenteral feedings may be necessary during exacerbation.

RDN Role: A thorough food history or frequency questionnaire to determine any food avoidance issues is needed. Patient education (possibly including a low-FODMAP diet) and support through initial phases, treatment and remission are standard.


Prevalence: Unknown, although estimates in the healthy population are 2.5% to 22%, depending on the diagnostic test used; substantially higher rates in older adults and those with predisposing conditions such as diabetes, celiac disease, Crohn’s disease, cirrhosis, cystic fibrosis, chronic pancreatitis, scleroderma, achlorhydria, short bowel syndrome and all anatomical pathology associated with small intestinal obstruction; considerable overlap of SIBO and IBS symptoms, which may contribute to underdiagnosing SIBO

Trend: Unknown

Other indicators: Indicators vary widely and may include nausea, abdominal pain and bloating, flatulence, fecal urgency and weight loss. There also is evidence of nutritional deficiencies, including fat-soluble vitamins, iron and vitamin B12. Elevated folate levels also may be seen.

Diagnostic criteria: There currently are no validated tests for diagnosing SIBO. However, breath tests of exhaled gas (hydrogen and methane) are most common, as they detect gases produced by bacteria following the ingestion of lactulose, glucose or xylose.

Treatment: Antibiotics are the primary treatment. Small bowel prokinetics may be used and stopping use of proton pump inhibitors may be helpful. Dietary measures include hydration, correcting nutritional deficiencies and adding probiotics. Symptom management techniques such as a low-FODMAP diet and the avoidance of fermentable foods have been particularly effective in patients who also have IBS.

RDN Role: RDNs provide patient support and education for symptom management, as well as nutritional management to halt weight loss and correct specific nutritional deficiencies such as iron and vitamins A, B12, D and E. Guidance on a low-FODMAP diet may be given, if applicable.


Prevalence: 0.7% among healthy people in the U.S.; 4.5% among people with first-degree relatives who have celiac disease; 0.4% of African-American, Hispanic and Asian-Americans.

Trend: Stable

Other indicators: Digestive symptoms more common in infants and children; only one-third of adults with celiac disease experience diarrhea. In children, recurring bloating, weight loss, failure to thrive and delayed puberty; in adults, IBS-like presentations, unexplained/ non-responsive iron deficiency anemia, first- or second-degree relative with celiac disease or other autoimmune disorder; some celiac disease is asymptomatic.

Diagnostic criteria: Small intestine biopsy is the gold standard diagnostic test and serologic tests for immunoglobulin A (IgA) are typical for screening purposes. Testing for genetic markers DQ2 or DQ8 can indicate likelihood of celiac disease if other tests are inconclusive.

Treatment: Lifelong gluten-free diet (avoidance of wheat, rye, barley, malt and oats not labeled as “gluten-free”)

RDN Role: Substantial diet education, correction of nutrition deficiencies and regular monitoring (especially for adequate amounts of B vitamins, iron, dietary fiber and calcium) are key


Prevalence: Annually, 17% of Americans get sick from contaminated food and 3,000 people die; Salmonella, Clostridium perfringens, Eschericihia coli (0157:H7), Staphylococcus aureus, Campylobacter jejuni and Listeria monocytogenes are among the most common causes of foodborne illness

Trend: Varies, depending on bacteria and method used to assess incidence

Other indicators: Abdominal pain and cramps, vomiting, nausea, headache, high fever, dehydration

Diagnostic criteria: Stool culture is a definitive test, though positive in fewer than 40% of cases and not commonly performed. Polymerase chain reaction testing can provide pathogen-specific results to narrow treatment options. Physicians use medical, dietary and travel history, along with symptoms and time of onset, to make a differential diagnosis.

Treatment: For those who seek treatment, hydration to replenish fluid losses and oral rehydration solution may be utilized. Antiemetic and antidiarrheal medications may be given, although they are not recommended for children. Antibiotics may be given, if needed.

RDN Role: Symptom management and rehydration education are provided. For immunocompromised patients, instruction on foods to avoid may be warranted. Consumer education focused on basic safe food handling and preparation methods, including proper hand-washing, can be given.


Prevalence: It’s estimated that highly contagious norovirus, the leading cause of foodborne illness in the U.S., causes an average of 570 to 800 deaths and 19 million to 21 million cases of acute gastroenteritis each year in the U.S. Prior to a vaccine being introduced in 2006, rotavirus was responsible for 20 to 60 deaths and more than 400,000 doctor visits annually for children younger than 5.

Trend: Rotavirus is decreasing; a new norovirus emerges every two to four years, usually leading to increased outbreaks worldwide.

Other indicators: Nausea, vomiting and cramping; additional flu-like symptoms including headache, chills, muscle aches, low-grade fever and fatigue are less common. Diarrhea is more common in children; vomiting is more common in adults.

Diagnostic criteria: Lab analysis on stool samples

Treatment: Hydration to replenish fluid losses; oral rehydration solution may be utilized. Antiemetic and antidiarrheal medications may be given for norovirus, although antiemetics are generally for adults only and antidiarrheal agents should not be given to children under 3.

RDN Role: Symptom management and rehydration education are provided. RDNs also may be involved in prevention by presenting education on food safety and sanitation for consumers and foodservice workers, especially those in post-acute care settings, health care facilities, restaurants and schools.


Prevalence: Varies by type; diarrhea-causing intestinal parasites typically found in U.S. include Giardia, Cryptosporidium and Cyclospora.

Trend: Rising for Cryptosporidium and Cyclospora; decreasing for Giardia

Other indicators: Cramping, vomiting, gas, weight loss

Diagnostic criteria: Stool examination (may require multiple samples); antigen assays also may be used for Giardia and Cryptosporidium infection diagnoses

Treatment: Hydration to replenish fluid losses; anti-diarrheal medications may be given. Other medications vary depending on the parasite.

RDN Role: RDNs provide symptom management and rehydration education; they also may be involved in prevention by offering consumer education focusing on proper hand-washing, safe food preparation, safe water practices and thorough cooking of food.


Prevalence: Unknown

Trend: Unclear; may be rising due to increased use in food supply

Other indicators: High intake of foods containing sugar alcohols (especially when first introduced to the diet, or when consumed in large doses or alone and not part of a meal) and polyols such as sorbitol, mannitol, maltitol, isomalt, xylitol — all of which are associated with diarrhea.

Diagnostic criteria: Food history indicating consumption of sugar alcohols

Treatment: Avoidance of or limiting sugar alcohols; research indicates consuming up to 15 grams per day is tolerated by most people.

RDN Role: Patient education about the effect of sugar alcohols in the body, how to identify them on the food label and emphasis on portion control of products that contain sugar alcohols.


Prevalence: Unknown, although more than 700 drugs are known to cause diarrhea, including antibiotics, laxatives, chemotherapy drugs and magnesium-containing antacids.

Trend: Unknown

Other indicators: May be more common in older adults, those taking multiple medications, residents of skilled nursing facilities or those with long hospitalizations. Approximately 20% of diarrhea following antibiotic treatment is caused by C. difficile infection.

Diagnostic criteria: Detailed medication history to look for common diarrhea-inducing medications (antibiotics, laxatives, chemotherapeutic agents, antihypertensives, nonsteroidal anti-inflammatory drugs, acid-reducers, protease inhibitors, antiarrhythmics); rapid detection assay for C. difficile

Treatment: Stopping or switching medications, although in some cases antidiarrheals are given instead of stopping medication; general dietary measures for symptom management include hydration, introduction of probiotics for antibiotic-associated diarrhea and C. difficile-related diarrhea, gradually increasing fiber content of diet.

RDN Role: Patient support and education for general symptom management

Self-diagnosis of conditions related to diarrhea is not advisable. Anyone experiencing these symptoms should see a physician and work with an RDN. Not all RDNs have advanced training in or experience with GI conditions, so it’s important to seek out one who does.

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Kitty Broihier
Kit Broihier, MS, RD, LD, is a writer, nutrition instructor and recipe developer based in South Portland, Maine. She is president of NutriComm Inc., a food and nutrition communications consulting company. Find her work on and, and follow her on Facebook, LinkedIn, Pinterest and Twitter.