What if the Low-FODMAP Diet Doesn’t Work?

Research has shown that the low-FODMAP diet works for around 75% of people. But what if the low FODMAP diet doesn’t work for you? If you have followed the low FODMAP diet Elimination Phase for as much as six weeks or more and still have not experienced adequate relief from your symptoms of Irritable Bowel Syndrome (IBS), something else could be going on. Do not stay in the Elimination Phase of the low FODMAP diet for longer than six weeks. A FODMAP-trained dietitian will help you to discover if any of the following may be occurring:

Your diet still includes too many FODMAPs

When the low FODMAP diet doesn’t work, sometimes it could be because you haven’t seen “hidden” FODMAPs. This is where they can be hiding: 

  • Be mindful of high FODMAP ingredients found on food, drink, medications or supplement labels. Some “sneaky FODMAPs” to look out for include fructose, honey, inulin/chicory root, FOS, mannitol or sorbitol. See the food label below for an example.
  • Watch out for FODMAP stacking from consuming too-large serving sizes or meals and snacks spaced a bit too close together
  • Read menus and labels of restaurant foods or to-go items from your local deli or grocery store
  • Watch out for gluten-free items that don’t contain wheat but DO contain other high FODMAP items – read labels!

Anything underlined in red on this food label is a high FODMAP ingredient. Anything underlined in blue has not been tested yet for FODMAPs but is most likely high FODMAP on this label. Molasses is underlined in green and is low FODMAP because it’s located near the last three ingredients.

Lactose Intolerance

Lactose intolerance – with this condition, you can’t fully digest the sugar (lactose) found in dairy products.

Though not life-threatening, but lactose intolerance can trigger symptoms and affect your lifestyle. Most symptoms start within 30 minutes to 2 hours after you have milk or food that contains it.  The low-FODMAP diet can be a great investigative tool to help you discover if you are lactose intolerant.

If you think lactose may be your issue, ask your gastroenterologist for a hydrogen breath test.  This test looks for a higher-than-normal amount of hydrogen in the breath, caused by the extra gases produced by the bacteria fermenting the undigested lactose in the intestines. Fortunately, many people with lactose intolerance can still enjoy foods that contain trace amounts of lactose.  

High-FODMAP Sources of Disaccharides (Lactose)

  • Buttermilk
  • Cows milk (skim, reduced fat, regular)
  • Custard
  • Evaporated milk
  • Ice cream (more than 2 scoops or over 88g)
  • Kefir
  • Yogurt (from cows milk, low fat and regular)

*Remember lactose intolerance should not be confused with a dairy allergy – they are very different.  A food allergy involves the body’s immune system where an adverse reaction to a food can result in severe symptoms that can even be life-threatening. If you suspect an allergy, please contact your physician.

What are the symptoms of a milk allergy?

Milk allergy symptoms can come on very rapidly. Symptoms include:

  • Skin rashes or hives
  • Swollen tongue or lips
  • Wheezing and chest tightness
  • Itchy, red and watery eyes
  • Difficulty breathing
  • Vomiting, feeling sick of diarrhea

Gut irritants may be to blame

Some foods that are low FODMAP may still be problematic for you as they can also be gut irritants. These include coffee, alcohol, high-fat meals, spicy foods, and NSAIDs.

Stress is still an issue for you

As we’ve discussed in my FREE Low-FODMAP Diet Wellness Course, stress, as well as anxiety and depression, can trigger IBS symptoms.  Sometimes just getting yourself worked up about whether or not you’ll have an episode at an event or party can be the main trigger for your symptoms! It can be a challenging cycle. 

Something else is happening, such as other foods or a food chemical intolerance

Another example when you think you have IBS and the low FODMAP diet isn’t working is histamine intolerance.

Histamine is a compound released by cells when they are triggered by an allergen, a food or certain bacteria. Intolerance to histamines leads to runny nose, watery eyes, itching, skin rashes, reflux, and myriad other symptoms. Individuals with histamine intolerance may also exhibit symptoms that overlap with IBS, such as diarrhea, constipation, abdominal pain and belching.

Histamine intolerance results when the body accumulates histamine and cannot completely degrade it properly. This may happen in situations where an individual lacks sufficient enzymes (Diamine Oxidase or DAO is the main enzyme that breaks down histamines) or they consume a large number of foods high in histamines. In addition, some gastrointestinal diseases can also contribute to a decline in histamine-degrading enzymes.

Other common food chemicals (which may be naturally-occurring or added to foods during processing) that may cause issues in some sensitive individuals include salicylates, amines, glutamates or artificial flavors or colors. Learn more about histamine intolerance here (Kate Scarlata, MPH, RDN).

You are still badly constipated

Work with your gastroenterologist to be tested for methane + SIBO. Methane gas production in your gut may be associated with constipation. Kate Scarlata, MPH, RDN suggests you “also discuss with your GI doc if he/she thinks you may be suffering from dyssynergic defecation. Dyssynergic defecation occurs when the muscles and nerves in your rectum don’t work properly to help you have a BM (bowel movement). This condition can be successfully treated with pelvic floor physical therapy (yes, it works) and/or biofeedback.”

You have IBS but are not especially sensitive to FODMAPs

In this case, you may benefit from another dietary approach. A team that includes a GI-trained dietitian and a gastroenterologist can help guide you.

Do you have Bile acid diarrhea (BAD)?

This can occur if you make more bile than you need or it is dumped into your intestine too quickly. Speak with your gastroenterologist to rule out BAD for you. Bile Acid Diarrhea: Prevalence, Pathogenesis, and Therapy US National Library of Medicine National Institutes of Health

What about Inflammatory Bowel Disease (IBD)?

People with IBD may also have IBS symptoms, however, IBD is not a functional gastrointestinal bowel disorder like IBS. IBD is a chronic inflammatory disease of the gut that may change the structure of the intestines. IBD includes Crohn’s Disease and ulcerative colitis. Symptoms of IBD include diarrhea that has persisted for more than 2 weeks, rectal bleeding, inflammatory mass, weight loss, perianal disease, and fever (source).

IBD can be diagnosed with imaging tests and the condition is usually managed with drugs and dietary changes. Surgical options may also be used to treat IBD, depending on the damage to the intestines. IBS may be managed with drugs as well, but unlike IBD, many people with IBS can often find relief through diet and lifestyle changes, and the gut is not damaged by IBS as it can be with IBD.

It’s actually Endometriosis

An estimated 1 out of 10 women in the United States suffer from endometriosis, however many remain undiagnosed.  For some women with endometriosis, they’ll notice strong abdominal pain and cramping, particularly during their period. 

Digestive symptoms from endometriosis which can confuse a patient or lead the doctor to misdiagnose for IBS include pain with a bowel movement, and difficulty having a bowel movement. A woman may also experience infertility, pain during sex or rectal bleeding. And, severe abdominal pain from endometriosis may be accompanied by nausea, diarrhea, and/or vomiting.

If you think your symptoms could be endometriosis, ask your doctor or gynecologist about getting a pelvic exam, ultrasound or laparoscopy.

That pain could be gallstones

If you feel a sharp pain on the right side of your belly or between your shoulder blades it could be a gallstone – you may not be able to sit comfortably or may have trouble getting up. You may also find that after eating something high in fat sends you sprinting to the bathroom with diarrhea.

A stabbing pain, a high fever with chills or skin or eyes that start to yellow, means it’s time to call your doctor right away.  While living in Boston in 2005, I was misdiagnosed with acid reflux by three doctors until a fourth doctor finally ordered an abdominal ultrasound and found a cluster of gallstones – the reason behind my pain at night and diarrhea.

Maybe it’s dumping syndrome

Dumping syndrome occurs when food, especially sugar, moves too fast from the stomach to the duodenum—the first part of the small intestine—in the upper gastrointestinal (GI) tract. This condition is also called rapid gastric emptying. Dumping syndrome has two forms, based on when symptoms occur:

  • Early dumping syndrome—occurs 10 to 30 minutes after a meal
  • Late dumping syndrome—occurs 2 to 3 hours after a meal. For more info: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
  • PLEASE NOTE: Dumping syndrome may be an issue for some individuals, but it is not a common complication of IBS. The most common causes of dumping syndrome are diabetes, bariatric surgery, gastrectomy, vagotomy or esophagectomy.

Could it be small intestinal bacterial overgrowth (SIBO) in addition to IBS?

If this is the case, your dietitian might suggest you see your gastroenterologist for a breath test. The most common symptoms of SIBO are very similar to symptoms of IBS. They include Abdominal bloating and distension, constipation, diarrhea, abdominal pain or discomfort, excessive gas or belching. Other SIBO symptoms uncommon to IBS are weight loss, acid reflux or heartburn.

With SIBO, you might notice that:

  • Fiber worsens your constipation.
  • An improvement in IBS symptoms when taking antibiotics.
  • You have celiac disease or are gluten intolerant and still cannot find relief from symptoms of IBS on a Low FODMAP and gluten-free diet.
  • You feel more gas and bloating when you take probiotics that contain prebiotics (fermentable fibers).
  • Developing chronic symptoms of gas, bloating, constipation, or diarrhea after taking pain medications, like opiates.
  • Your blood work shows chronically low iron or ferritin with no known cause.

For more information on SIBO, please read: 4 Facts About SIBO the Internet Keeps Getting Wrong by Tamara Duker Freuman, RD

Unexplained anemia, other lab work revealing low levels of any nutrient

Unexplained anemia or low levels of any nutrient …can be associated with malabsorption of nutrients and are sometimes seen in medical conditions that affect the gastrointestinal tract as the small intestine is the site of most nutrient absorption and it can become damaged in certain inflammatory conditions of the gut. (Vitamin D may be an exception here. While low vitamin D blood levels can certainly affect people with gastrointestinal conditions, it is not a nutrient that naturally occurs in food. Low vitamin D levels are common, and not necessarily a sign of malabsorption.)” – Patsy Catsos, MS, RDN, LD.

Unexplained weight loss

If you’ve lost a few pounds and haven’t changed your diet or exercise habits, call your doctor.

Extreme fatigue

Extreme fatigue is not a symptom of IBS but could occur due to chronic fatigue syndrome, sleep apnea, cancer, thyroid disease, multiple sclerosis, anemia, acute liver failure, and other conditions. Talk with your doctor if this is a problem for you. 


Pancreatitis may come with IBS-like symptoms such as diarrhea, bloating, and belly pain. “The pancreas is an organ located in the abdomen. It plays an essential role in converting the food we eat into fuel for the body’s cells. The pancreas has two main functions: an exocrine function that helps in digestion and an endocrine function that regulates blood sugar.” (Columbia University, Department of Surgery, The Pancreas Center). Talk with your doctor if this sounds like something you are experiencing.

The bottom line:

Again if you have been on the low-FODMAP diet for six weeks or more, please consult with a FODMAP-trained dietitian to see if you can both discover if you are simply not following the diet correctly or if an underlying diagnosed or undiagnosed condition is to blame for your gastrointestinal symptoms.

About The Author

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top