What is IBS and Why Do Symptoms Improve on a Low Carb Diet?

Quite a few physicians that I know that recommend a low-carb diet to their patients have mentioned to me that those who had previously been diagnosed with Irritable Bowel Syndrome (IBS) and who suffered for years reported significant improvements within a short time of adopting the dietary changes and have asked me why. That is the topic of this article.

Prior to expanding my Dietetic practice to include this low carb division a little over 4 years ago, my main focus was on helping people who were dealing with food allergies and food sensitivities; including Celiac disease, Mast Cell activation disorder (MCAD) / histamine intolerance, fructose intolerance and Irritable Bowel Syndrome  For many of my clients, it was the gastrointestinal (GI) symptoms that caused them to seek out my help in the first place.

What is IBS?

I have often thought of Irritable Bowel Syndrome (IBS) as the diagnosis that people receive when all the other possible options have been ruled out. For the most part, by the time people are told that they have IBS, they already know for sure that they don’t have Celiac disease or inflammatory Bowel Disease (IBD) such as Ulcerative Colitis or Crohn’s, and they don’t have diverticulosis ⁠—as each of those diagnoses are confirmed after a colonoscopy and/or a biopsy, and are often supported with underlying blood test results.

What makes IBS different is that it is a functional GI disorder ⁠— which means there is no structural or biological abnormality that can be measured on routine diagnostic tests.

Of course a person experiencing  a bout of diarrhea or constipation, or abdominal pain does not mean that person has a GI disorder or disease. Those symptoms could be the result of a virus, bacteria, food-borne illness (“food poisoning”) or food sensitivities. Once these have been ruled out, if the symptoms recur over and over again over time, then investigation as to what else it could be is often begun.

How is IBS Diagnosed?

While many of the symptoms of IBS and Celiac disease can be quite similar, including diarrhea and abdominal pain and bloating, there are very specific indicators that a person may have Celiac disease that clinicians such as myself notice as evidence to request further testing. The first stage in ruling out Celiac disease is an ordinary blood test looking for an antibody to gluten. If that comes back positive, then the person is referred to a Gastroenterologist for an endoscopy. If the blood test is negative, the next step may be for the person to be scheduled for a colonoscopy.

A colonoscopy which is where the inside of the large intestine (colon) is examined using a flexible probe about 1/2″ in diameter that’s fitted with a light and telescopic camera at one end and endoscopy is where a fine, flexible probe fitted with a light and telescopic camera is inserted via the mouth to view the esophagus, stomach and the upper part of the small intestine.

Celiac disease will be ruled out or confirmed using endoscopy, as the upper small intestine is where the damage to the villi (little hair-like projections on the wall that increase the surface area in order to help absorb nutrients from food) will be visible, or not.

A colonoscopy enables the Gastroenterologist to see what the lining of walls of the colon look like and to look for physiological signs of diverticulosis (little bulges or “pouches” in the colon) or signs of inflammation and damage consistent with Inflammatory Bowel Disease (IBD), such as Ulcerative Colitis or Crohn’s and to rule out colon cancer.

If the endoscopy and colonscopy come back normal, the person is often told that their symptoms of diarrhea or constipation (or both alternating), flatulence (“gas”), bloating, abdominal pain or cramping, mucous in the stool is Irritable Bowel Syndrome (IBS).

Prevalence of IBS

According to the International Foundation for Gastrointestinal Disorders (IFFGD), approximately 10-15% of the population have IBS; with 40% having a mild form, 35% having a moderate form, and 25% having severe IBS. While many people think of IBS as being a woman’s health issue, 35% to 40%  of people with IBS are men and 60-65% are women [1]. IBS is so common, that it is estimated that 12% of all visits to primary care providers (family doctors) is related to symptoms of IBS [1].

Once a person receives a diagnosis of IBS the first question that is often asked is “now what?” Physicians will often suggest their patients try following a “low-FODMAP diet” which I teach through my non-low-carb division.

Why Eating a Low-Carbohydrate Diet often Improves IBS Symptoms?

A low-FODMAP diet eliminates sources of very specific carbohydrates that are fermented by the gut bacteria and that result in the increased gas production that underlies the classic IBS symptoms of abdominal pain and bloating, and the water flooding into the intestine in response to these fermented carbohydrates is what causes the very common symptom of diarrhea. The constipation results when the contractions of the colon are impaired, resulting in the stool sitting longer in the colon resulting in more and more of the water being re-absorbed.

When people eat a low-carb diet, they either eliminate or greatly reduce sources of fructose (the sugar found in fruit and many processed foods, especially processed condiments like ketchup) and significantly reduce one of the key sources of fructans (inulin) found in wheat; which is a highly fermentable carbohydrate. Galactans, another fermentable carbohydrate found in beans, lentils and legumes such as soy is also eliminated or greatly reduced which is why people with IBS feel so much better after beginning eating a low-carb diet!

Before I taught a low-carbohydrate approach, I used to have people take the IBS Package before the Complete Assessment Package, so we could find out what foods underlie their unpleasant symptoms and eliminate them before I designed their Meal Plan. Now, if they are planning to adopt a lower carb lifestyle anyway, then I recommend they don’t take the IBS Package, as it may not be necessary.  I recommend focus on them adopting a diet that greatly reduces the sources of the fermentable carbohydrates mentioned above, plus a few more that I tell them about and see how they feel. If their symptoms are gone, then there is no reason for them to take the IBS Package!  If however, they feel quite a bit better but still have residual symptoms, then I may recommend that take the Low-FODMAP hourly consultation through my non-low carb division to learn which low-carb foods they may be best to avoid.

More Info?

If you would like more information about the IBS Package, you can find that under Services tab of my affiliate website, BetterByDesign Nutrition Ltd. and if you’re nterested in the low-FODMAP teaching, you can find that in the Shop on that site.

Of course, if you have questions please feel free to send me a note using the Contact Me form above, and I will reply as soon as I can.

To your good health!


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Foundation for Gastrointestinal Disorders (IFFGD),  https://www.aboutibs.org/facts-about-ibs/statistics.html

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