Diarrhea and Constipation: A Breakdown of Common Gastrointestinal Issues

By: Ana Garcia, CSUN Dietetic Intern Cohort 2021-2022 

Discussing bowel movements, commonly known as “poop”, may be an uncomfortable or embarrassing topic. However, the frequency of our bowel movements and the consistency of stools actually reveals a lot of useful information regarding our health and diet. After a meal, the coordinated contractions and relaxations of smooth muscles in the gut transport food throughout the intestines so water, electrolytes, and nutrients can be absorbed while waste is eliminated.Assuming normal gut function, a person can expect between 3 bowel movements per day to 3 bowel movements per week.2 

Normal bowel movements should be easy to pass and stools should be soft but firm and shaped like a sausage or snake. Stools that cause straining or are too hard or too watery in texture indicate that there is a problem in gut motility. Diarrhea and constipation are common gastrointestinal (GI) issues that most adults will encounter at some point in their lifetime.However, did you know that both of these GI issues can be efficiently prevented and managed with lifestyle changes?  

Factors That Affect Gut Motility 

Constipation is defined as infrequent bowel movements with hard, dry, or lumpy stools occurring less than 3x/week.4 In contrast, diarrhea is the passing of loose, watery stools more than 3x/day.Bowel movement frequency and stool consistency will depend on your physical activity level, hydration, and diet. Physical activity stimulates gut motility and communication between the gut and brain. 6-8  Being active increases muscle activity in your intestines and increased muscle contractions then help the gut move stool smoothly. Studies have shown that exercise may reduce transit time, meaning that stools will pass faster through the intestines and this limits the amount of water your body will absorb from the stools.6,9-10  Running, jogging, walking, and other types of exercise that add weight-bearing and jarring movements to the body are beneficial to gut motility.  

Proper hydration is important because water helps stools pass smoothly through the digestive tract. As stools move through the colon, water is absorbed. When you are dehydrated, your body will try to keep a fluid balance by reabsorbing more fluid back from stools. Stools may already contain very little water due to improper hydration and water absorption in the colon will result in dry, hard stools that are difficult and painful to pass.8 Therefore, dehydration is a common contributor to constipation. Make sure that you consume at least 8-10 cups of water per day to maintain your body properly hydrated.  

In addition to getting adequate physical activity and water in your daily life, consume the recommended amount of fiber. Fiber plays a role in increasing stool weight, microbial mass, fluid, and transit time.Fiber is a type of carbohydrate that our bodies cannot digest. There are two types of fiber: insoluble and soluble. Insoluble fiber acts as a bulking agent to stool and helps clean out the colon.11  Soluble fiber retains water by forming a gel-like consistency, which helps stool pass more quickly.12  Soluble fiber also helps control blood sugar and reduces cholesterol. Many foods may have both soluble and insoluble fiber, such as fruits and vegetables. Insoluble fiber also comes from grains. Soluble fiber comes from oats, beans, peas, lentils, and barley. Most soluble fibers will normalize stool after having diarrhea or constipation.13 Unfortunately, the average American only consumes about half of the recommended fiber intake, which is 25-28 grams per day.  

Managing Constipation 

Although constipation is preventable and manageable, it is a common gastrointestinal issue among all ages and populations in the United States. The probability of having constipation increases with age, given that about 16% of adults have symptoms of constipation and 33% of adults 60 years of age and older experience constipation.14 Exact percentages may be even higher given that not all individuals will seek health care. Symptoms of constipation include abdominal pain, bloating, gas, the sense of incomplete emptying, and bloody stools. Additionally, hemorrhoids, anal fissures, and diverticulosis may occur from chronic constipation. Symptoms may be long-term or resolve in a short period.  

Constipation can be caused by physical inactivity, dehydration, lack of dietary fiber, medication side effects, or be a symptom of another medical problem. Medications such as iron supplements, calcium antagonists, opioids, anticonvulsants, diuretics, antacids, and anticholinergics are known to cause constipation.15 These drugs inactivate nerves in the gut or decrease activity of the smooth nerve muscles, which decreases gut motility. Anticholinergics, for example, are a medication group that blocks involuntary muscle movement to treat Parkinson’s, urinary incontinence, and COPD, but as a result affect gut motility.16  Gut motility disturbances may also be caused due to diabetes, hypothyroidism, Parkinson’s disease, spinal cord disorders, irritable bowel syndrome (IBS), and stroke. Diabetes, for example, delays gastric emptying because high blood sugar damages nerves.14  

To improve constipation without worsening bloating and flatulence, slowly add fiber in your diet over 2 to 3 weeks. Aim to make half of your grains whole grains such as whole wheat bread, tortillas, rice, and cereals.17 Trial a psyllium husks supplement to help constipation since it can improve transit time, gas and bloating. Psyllium husks have a very slow fermentation rate in the gut with a good laxative effect.13 Use the chart below to find what foods are high in fiber. 

High Fiber Foods (To Manage Constipation)

ArtichokesRaspberriesBlack beansFiber One
Baked potato with skinMangoKidney beansAll Bran
BroccoliPear with skinNavy beansShredded Wheats
Brussel SproutsOrangeLentilsCheerios
SpinachPrunesPinto beansWheaties
PeasAppleSoy beansGranola

High Fiber Breakfast Ideas

– Oatmeal topped with raisins, berries, or bananas
-Rye/wheat bread with avocado topped with germ sprouts

Managing Diarrhea 

Diarrhea may be caused by viruses, contaminated food, lactose intolerance, side effects of chemotherapy, radiotherapy, antibiotics, or be a sign of other disorders such as IBS, Crohn’s disease, and ulcerative colitis. Pathogenic microorganisms may produce toxins that cause colitis (inflammation of the colon) and increased secretion of fluid and electrolytes. The purpose of antibiotics is to kill bacteria causing bacterial infections but antibiotics also decrease the number of beneficial bacteria in the gut, resulting in decreased fermentation byproducts and thus reducing absorption of electrolytes and water. Overuse of antibiotics has led to an increase in antibiotic-associated diarrhea and Clostridium difficile (C. diff),  which is the leading cause of hospital-acquired diarrhea.Symptoms of diarrhea may include bloody or black stool, dehydration, dry mouth, flatulence, loss of appetite, weight loss, insufficient urine production, fever, and abdominal pain.18  

An important aspect of diarrhea management is replenishing fluid and electrolyte loss. Drink diluted fruit juice, Pedialyte, or Gatorade. 14 In more severe cases of diarrhea, IV fluid rehydration may become necessary. For proper water absorption of the stool, increase fluids at every meal and throughout the day.  Healthy people need 8 to 10 cups of fluid each day but you may need to drink more to replace fluids lost with diarrhea. Adding soups and broths is an easy way to replenish fluid and electrolyte loss.  

When experiencing diarrhea, make sure you avoid foods high in fiber and sugar. A low fiber diet reduces the frequency and volume of stools, lessening irritation to the GI tract and allowing it to heal. Sugar stimulates fluid secretion from the GI tract, and sugar alcohols have a laxative effect, both of which are undesirable during diarrhea episodes. Overall, any food that may be difficult to digest and irritates the intestine should be avoided.11,16  See the table below. 

Managing Diarrhea

Increase Low Fiber Foods Decrease the FollowingEasy to Tolerate Meals 
½ Banana Caffeine Chicken Rice Soup 
White Rice Sugar Alcohols Mashed Potatoes 
Applesauce High Fat Foods Peanut Butter Sandwich on White Bread 
White Toast Spicy Foods Plain Bagel  

Resources on Campus 

If you are experiencing diarrhea or constipation frequently and require more individualized recommendations, set up an appointment with a Registered Dietitian Nutritionist (RDN). The Marilyn Magaram Center has telehealth (virtual) nutrition counseling available through https://www.csun.edu/marilyn-magaram-center/products-services. If you are a currently enrolled student, the Klotz Student Health Center offers nutrition counseling for students. Visit their website (https://www.csun.edu/shc) or call (818) 677-3666 to schedule an appointment. 

Also, visit the Marilyn Magaram Center Youtube Channel to find more high fiber recipes such as this quinoa salad.


  1. Olsson C, Holmgren S. Autonomic control of gut motility: a comparative view. Autonomic neuroscience. 2011;165(1):80-101. Accessed November 15, 2021.  https://doi.org/10.1016/j.autneu.2010.07.002.
  1. National Institutes of Health: National Cancer Institute. Bowel Movement. Accessed November 15, 2021.  https://www.cancer.gov/publications/dictionaries/cancer-terms/def/bowel-movement.
  1. Mahan L, Raymond J. Krause’s Food & the Nutrition Care Process. 14th ed. St. Louis, MO: 2017.  
  1. Cho K, Jo Y, Song B, et al. Colon transit time according to physical activity and characteristics in South Korean adults. World journal of gastroenterology. 2013;19(4):550–555. Accessed November 16, 2021.  https://doi.org/10.3748/wjg.v19.i4.550.
  1. World Health Organization. Diarrhoeal Disease. Published 2017. Accessed November 15, 2021.  https://www.who.int/news-room/fact-sheets/detail/diarrhoeal-disease.
  1. Molina M, Lunardi B, Wang D, et al. Exercising the hepatobiliary-gut axis. The impact of physical activity performance. European journal of clinical investigation. 2018;48(8),e12958. Accessed November 16, 2021. https://doi.org/10.1111/eci.12958.
  1. Oruç Z, Kaplan M. Effect of exercise on colorectal cancer prevention and treatment. World journal of gastrointestinal oncology. 2019;11(5):348–366. Accessed November 16, 2021.  https://doi.org/10.4251/wjgo.v11.i5.348.
  1. Royes L. Cross-talk between gut and brain elicited by physical exercise. Biochimica et biophysica acta. Molecular basis of disease. 2020;1866(10): 165877. Accessed November 16, 2021. https://doi.org/10.1016/j.bbadis.2020.165877.
  1. Niv E, Halak A, Tiommy E, et al. Randomized clinical study: partially hydrolyzed guar gum (PHGG) versus placebo in the treatment of patients with irritable bowel syndrome. Nutr Metab. 2016;13:10. Accessed November 15, 2021. https://pubmed.ncbi.nlm.nih.gov/26855665/
  1. American Heart Association. Whole Grains, Refined Grains, and Dietary Fiber. Accessed November 17, 2021. https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/nutrition-basics/whole-grains-refined-grains-and-dietary-fiber.
  1. Kaiser Permanente. Fiber facts: Why Fiber is Important. Published 2016. Accessed November 17, 2021. https://mydoctor.kaiserpermanente.org/ncal/Images/915800109%20Revised%208-10_tcm75-14335.pdf.  
  1. Stewart E. Irritable Bowel Syndrome — An Overview of Treatment Options. Today’s Dietitian. 2014;(16)4:46. Accessed November 17, 2021. https://www.todaysdietitian.com/newarchives/040114p46.shtml.
  1. Myhrstad M, Tunsjo H, Charnoc K, et al. Dietary Fiber, Gut Microbiota, and Metabolic Regulation-Current Status in Human Randomized Trials. Nutrients. 2020;12(3):859. Accessed November 17, 2021. file:///C:/Users/wic-user/Downloads/nutrients-12-00859-v2.pdf.
  1. Nemeth V, Pfleghaar N. Diarrhea. StatPearls. Updated 2021. Accessed November 17, 2021.  https://www.ncbi.nlm.nih.gov/books/NBK448082/.
  1. National Health Institute. Symptoms and Causes of Constipation. Published 2018. Accessed November 17, 2021.  https://www.niddk.nih.gov/health-information/digestive-diseases/constipation/symptoms-causes#medicines.
  1. Harvard Health. What to do when medication makes you complicated.  Published 2019. Accessed November 17, 2021. https://www.health.harvard.edu/staying-healthy/what-to-do-when-medication-makes-you-constipated#:~:text=These%20medications%20block%20the%20effects%20of%20acetylcholine%2C%20a,because%20of%20a%20digestive%20system%20that%27s%20off%20balance. 
  1. Niv E, Halak A, Tiommy E, et al. Randomized clinical study: partially hydrolyzed guar gum (PHGG) versus placebo in the treatment of patients with irritable bowel syndrome. Nutr Metab. 2016;13:10. Accessed November 15, 2021. https://pubmed.ncbi.nlm.nih.gov/26855665/
  1. Halland M, Bharucha A.Relationship between control of glycemia and gastric emptying disturbances in diabetes mellitus. Clinical Gastroenterology and Hepatology. 2016;14(7):929-936. Accessed November 16, 2021. 

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