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Getting to the bottom of diarrhea

Reading time: 9 minutes

How do you solve a problem like diarrhea? Dietitian Sandra Mikhail details the tests you need to know about for a troublesome tum and what you can do now to ease symptoms fast.

Diarrhea has no consideration of place and time. I had one of the worst poop experiences of my life on a moving train in Egypt on the way to see the pyramids, after eating a cheese sandwich from the coffee cart. The toilet was a hole in the floor, and I had the man I was dating manning the door and asking whether I needed support to “balance” myself.

The type of diarrhea I experienced is known as acute, usually defined as three or more loose or watery stools per day, lasting less than four weeks. This tends to be the most common form and is mainly infectious in nature, meaning you’ve possibly contracted a bacterial, viral or parasitic infection. We’ve all heard of the “stomach flu,” also known as viral gastroenteritis, and that tends to be one of the most common causes.

If diarrhea persists, there’s a chance you may be dealing with something more than just an acute bout of loose poo. It’s classed as chronic if it lasts longer than four weeks, and working out the cause is much more complex. A long list of underlying issues and conditions need to be ruled out.

Here’s a guide to the investigations to perform and possible causes to consider if you suffer from chronic diarrhea, as well as what you can do to ease those tummy troubles straightaway.

Uncovering the cause

There are several tests I generally recommend as an investigative starting point.

Depending on the results, a colonoscopy (when a camera is used to look inside your rectum and colon) may be warranted. Keep in mind that although some conditions can seem scary when learning about what they are, more often than not, the cause of chronic diarrhea is manageable and is not life-threatening.

Some of the potential causes include:

  • Celiac disease
  • Inflammatory bowel disease (IBD)
  • Irritable bowel syndrome (IBS)
  • Small intestinal bacterial overgrowth (SIBO)
  • Bile acid malabsorption
  • Food intolerances and allergies
  • Infections such as C. difficile
  • Pancreatitis
  • Bowel cancers

Diarrhea can also be a side-effect of some medications, such as:

  • Antibiotics, in particular macrolides (e.g., erythromycin)
  • Non-steroidal anti-inflammatory drugs (NSAIDs, e.g., ibuprofen)
  • Magnesium-containing products
  • Hypoglycemic agents (e.g., metformin)


Symptoms of irritable bowel syndrome (IBS), which include bloating, abdominal pain or discomfort, flatulence, diarrhea and/or constipation, are similar to those experienced by people with small intestinal bacterial overgrowth, or SIBO.

What is SIBO?

SIBO is diagnosed when there are excessive numbers of bacteria in the small intestine. In a healthy digestive system, the number of gut bacteria in the small intestine is quite low, so when the number is excessive, it is often the result of an anatomical abnormality or digestive illness.

The most common conventional causes are related to motility disorders (i.e., conditions that slow movement of food through the small intestine); structural problems present along the small intestine, such as adhesions; or medical conditions that can impact the motility of food in the small intestine, such as Crohn’s disease and diabetes.

Anywhere from 4 to 78 percent of patients with IBS also have SIBO. That’s a pretty wide gap. But this is because the medical community hasn’t yet landed on one standardized test for diagnosing SIBO.

Diagnosing SIBO

Most cases are diagnosed through one of two types of hydrogen breath testing: the lactulose breath test (LBT) or the glucose breath test (GBT). Both tests measure concentrations of hydrogen and methane in the breath.

If your doctor prescribes this test, you will be asked to drink a sugar solution and then provide samples of your breath at various intervals. If hydrogen and/or methane is detected within 90 minutes, SIBO will be diagnosed.

The length of time is key—generally it would take two hours for the sugar solution to make its way to the large intestine, so any rise in these gases prior to that time suggests that the sugar was acted on by bacteria in the small intestine.

This method has considerable diagnostic limitations: it lacks sensitivity and specificity, which means there is a high chance of getting a false positive or false negative result.

The best method of diagnosing SIBO is sampling fluid from the small intestine and growing the bacteria found in this fluid to estimate whether a very high number of bacteria are present. Because it is an invasive procedure, it is rarely used in clinical practice unless a gastroenterologist thinks it’s necessary.

Oregano for SIBO 

If you’ve been diagnosed with SIBO, the main treatment is a certain type of antibiotic, one that is not absorbed in the stomach and therefore can make its way to the small intestine, where it can eliminate any bacteria it finds there. The most common one is rifaximin, aka Xifaxan.

But a great alternative is oregano oil, a natural antibiotic with the active ingredients thymol and carvacrol. Carvacrol fights against a variety of bacterial strains, while thymol acts as an anti-inflammatory agent in addition to its antibacterial, antiviral and antifungal effects.

Clarify with your gastroenterologist or dietitian that this approach would work for you. The protocol I use is a 180–200 mg oregano oil capsule, three times per day with meals for three to six weeks.

Food-related causes of chronic diarrhea

A lot of the time, the cause of chronic diarrhea is food related, and simple dietary changes can have a big impact. These possible causes include IBS, which can be helped with a low-FODMAP diet (reducing the amount of fermentable sugars in your diet); lactose intolerance, which can be resolved with a low-lactose or lactose-free diet; celiac disease (an abnormal immune system rection to gluten), which can be controlled by eliminating gluten from the diet; and bile acid malabsorption (BAM), which can be helped by limiting fat in the diet.

Initial investigations for chronic diarrhea

  • Full blood count
  • CRP (C-reactive protein, a marker of inflammation)
  • Urea and electrolytes
  • Celiac screen
  • Iron and ferritin levels
  • Vitamin B12
  • Fecal calprotectin (a marker of inflammation)
  • Fecal culture and parasites
  • Fecal elastase (to check pancreatic function)

Treating chronic diarrhea

While management of chronic diarrhea depends on the cause, whether food related or otherwise, there are four simple steps that are important for anyone suffering from diarrhea.

Step 1. Rehydration

The first line of therapy will always be correcting any electrolyte and fluid losses. Make fluid your best friend for the next 24 hours. The aim is to drink 2–2.5 L per day.

It is always best to have some oral rehydration solution (ORS) in your home pharmacy cabinet. ORSs are commonly bought as sachets or tablets and contain a mix of glucose, sodium and potassium to prevent dehydration. But you can easily make your own at home. Sip on this throughout the day.

Other beneficial fluid choices include bottled water, broth, diluted juice and sports drinks that contain salts such as sodium and potassium. However, it is best to avoid beverages such as sodas, fruit smoothies and milk-based beverages as they can make your
diarrhea more severe.

Watch out for these signs of dehydration: being thirsty, having dark-colored urine, urinating less than normal, feeling extremely tired and feeling dizzy. If you have any of these symptoms, you’ll need to drink more.

DIY rehydration solution

Here’s what the World Health Organization recommends for a 1-L rehydration solution using household measuring spoons for the quantities:


  • 1⁄2  tsp table salt
  • 1⁄2 tsp baking soda
  • 2 Tbsp table sugar
  • 4 1/4 cups (1 L) tap water (if safe to drink) or bottled water


  1. Add 2 cups (500 mL) of water to your bottle/container.
  2. Add the dry ingredients and stir or shake until they dissolve.
  3. Add the remaining water.

Step 2. Eat easy-to-tolerate foods

If your diarrhea and stomach cramps have settled, you’re probably ready for some real food, but naturally you won’t be rushing toward a creamy mushroom risotto or seafood chowder.

Start by including easy-to-tolerate foods that aren’t too high in fiber; that doesn’t mean, however, you should be eliminating fiber completely. As your diarrhea eases, the goal is to temporarily reduce the amount of insoluble fiber you are consuming until your stool is better formed. That means you can still have soluble sources of fiber.

We have moved beyond the outdated approach of BRAT—bananas, rice, applesauce and toast—which lacks any scientific backing yet was widely recommended by pediatricians and doctors to temporarily ease diarrhea. See the box on page 51 for a basic guide to foods you might tolerate well as you manage diarrhea.

Step 3. Limit foods known to worsen symptoms

Some foods are known to worsen diarrhea because they can cause more gas, bloating and loose stools by causing food to move through your gut too quickly. While diarrhea persists, it may be useful to avoid the following:

  • Caffeine in coffee, strongly brewed black tea and chai, cola and energy drinks
  • Foods high in insoluble fiber, such as whole-grain or multigrain breads and cereals, whole-grain pasta, whole nuts, broccoli, brussels sprouts, black beans, celery and lentils
  • Large amounts of fructose, the sugar found in honey, dates, dried fruit and apple juice, or too much fruit in one go
  • Fried or fatty food such as anything fried in butter, French fries, potato chips and pastries
  • Sugar alcohols found in diet foods, such as sugar-free gum, sweets and high-protein dairy products

Step 4. Supplement wisely

When it comes to easing diarrhea with supplements, you may find psyllium husk and the probiotic strains listed below are helpful.

Psyllium husk is often used to resolve constipation, but you can also use it to manage diarrhea thanks to its water-holding capacity in your bowel that bulks up watery, loose stools.

Suggested dosage: Day 1, start with 1⁄2 tsp in a glass of water (250 mL), then wash that down with another glass. Day 2, increase the amount to 1 tsp in a glass of water and wash it down with another glass

Lactobacillus rhamnosus GG (LGG) is a probiotic strain that is used to treat and prevent antibiotic-associated diarrhea and traveler’s diarrhea.

Suggested dosage: You can take this strain two hours after breakfast and dinner at 5–6 billion CFU, twice a day for the duration of your antibiotic course and for one week after

Saccharomyces boulardii lyo CNCM I-745 is a probiotic yeast that has also been used to prevent both antibiotic-associated diarrhea and traveler’s diarrhea.

Suggested dosage: It is commonly sold in sachets of 10 billion CFU; follow the instructions on the label

Enteroccocus faecium SF68 is a strain commonly found in Europe that I have used with my clients for both the prevention and treatment of any infectious type of diarrhea.

Suggested dosage: For diarrhea prevention, take two capsules daily for two weeks. For treatment, take three capsules daily for the first week, then reduce to two capsules by the second week

Tummy-friendly recipes

After a case of diarrhea, your appetite may not be the greatest, and the focus should be on rehydrating and gradually gaining your strength and energy through food as your appetite returns. The following recipe suggestions are best kept for when you are ready to introduce food, keeping insoluble fiber to a minimum.

Rice pudding

Ingredients (serves 4)

  • 4 1/4 cups (1 L) plant-based milk (soy or oat)
  • 1/2 cup (100 g) white rice
  • 1 Tbsp sugar (or 1/4 tsp stevia)
  • 1 cinnamon stick
  • 2 tsp vanilla

Toppings: Any fruit that you can tolerate


  1. Pour the milk into a medium-sized pot and bring to an intense simmer, just under boiling, then reduce the heat, add the rice and simmer over low heat to continue cooking.
  2. Add the sugar and the cinnamon stick and stir frequently for 35–40 minutes, until the rice is tender.
  3. Turn off the heat and stir in the vanilla. The mixture should resemble the consistency of runny porridge but will continue to thicken as it cools.
  4. Remove the cinnamon stick and transfer the pudding to a large serving dish. Allow the pudding to cool to room temperature, then refrigerate until you are ready to serve.

Lemon and green pea orzo (Risoni)

Ingredients (serves 4)

  • 1 Tbsp extra-virgin olive oil
  • 1 cup (200 g) orzo pasta
  • 1 Tbsp dried thyme
  • 1 small garlic clove, minced
  • 2 cups (500 mL) vegetable broth/stock
  • 1/2 cup (125 mL) oat or soy cream
  • Juice and zest of 1 small lemon
  • 1 1/2 cups (200 g) frozen green peas, thawed under warm water


  1. In a pan, heat the olive oil, then add the orzo and stir for about 1 minute until slightly toasted.
  2. Add the thyme and garlic and stir until fragrant and well combined.
  3. Add the stock, one ladle at a time, stirring until you’ve added it all. Bring to the boil then gently simmer, covered, for 10 minutes, until the pasta has absorbed the liquid.
  4. Remove the lid, then add the cream, lemon juice and zest, and peas. Stir until the peas are cooked but still bright green. (Note: try not to overcook the peas.)
  5. Season with salt and pepper and, as an optional addition, grate some parmesan cheese on top and serve.

Easy-to-tolerate foods

Breads, grains and cereals

  • Barley
  • Gluten-free pasta
  • Oats (cooked)
  • Regular pasta
  • Rice noodles
  • Semolina
  • Sourdough bread
  • Spelt bread
  • White bread
  • White flour
  • White rice


(temporarily opt for well-cooked instead of raw)

  • Asparagus tips
  • Carrots
  • Cucumber
  • Mushrooms
  • Potatoes (skinless)
  • Pumpkin (skinless)
  • Tomato paste and purée
  • Zucchini/courgette


(no more than two servings per day)

  • Avocados
  • Bananas
  • Blueberries
  • Honeydew melon
  • Mango
  • Oranges
  • Pears
  • Rock melon / cantaloupe
  • Seedless watermelon
  • Strawberries

Meat and alternatives 

(avoid tough, gristly meat)

  • Chickpeas (1⁄4 cup, canned, should be well tolerated)
  • Eggs
  • Lean beef
  • Poultry
  • Tofu

Dairy and alternatives

(temporarily choose lactose-free options)

  • Natural Greek yogurt
  • Oat milk
  • Soymilk and natural soy yogurts
  • Nuts and seeds
  • Smooth nut butter (e.g., almond butter)
  • Chia seeds
  • Ground flaxseeds

Adapted from The Gut Chronicles by Sandra Mikhail (Hammersmith Health Books, 2023)

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Article Topics: diarrhea, Gut Health, nutrition
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