By: Erin Slater RD LDN

 Although there are many triggers for the symptoms associated with Irritable Bowel Syndrome, diet alteration is commonly the first step taken by many people with IBS. Food is in our everyday world and it can be difficult to sort out what types are foods that seem to “trigger” IBS vs. those that are safe.

Several common categories of food are believed to trigger or increase the severity of symptoms during a flare. These include: caffeine, carbonation, alcohol, sugars, fatty or fried foods, and insoluble fiber. In addition, we are now looking at gluten in the absence of Celiac Disease to explain some symptoms of IBS.

Caffeine, Carbonation, and Alcohol

Caffeine naturally increases the motility of the gut, sometimes causing painful spasms and diarrhea. Likewise, carbonation and alcohol can increase motility, irritating a hypersensitive gut. Sources of caffeine can range from soda which has 25-50 mg of caffeine per serving to energy drinks which have up to 125 mg in one shot.

While some people can tolerate small amounts of caffeine, carbonation, and alcohol, a common recommendation is to discontinue all three triggers for a two-week period to evaluate any improvement.

Fatty and Fried Foods

Fatty or fried foods can also be difficult to digest, leading to gas, bloating and diarrhea. While fried foods may be easy to avoid, other culprits like nuts and nut butters, mayonnaise, and cooking oils may be harder to recognize in the food we eat. Begin by looking at labels and identify foods with less than five grams of fat per serving. In addition, try grilling or baking foods to avoid extra fat from cooking oils.


Fiber is likely to be the topic of conversation when a person mentions his/her IBS to family, friends, and physician. However, “eating more fiber” is not always as clear of a statement as it seems. There are two types of fiber: soluble and insoluble fiber. Insoluble fiber is usually what we think of as fiber. This includes bran from whole grain cereals and breads, some vegetables like broccoli and cabbage, and skin from root vegetables like the skin from potatoes.

Soluble fiber, however, is a different type of fiber. This fiber is usually associated with lowering cholesterol as can be found in oats, apples, and beans. This type of fiber attracts water and tends to form a gel which sweeps along the gut, catching cholesterol from your diet and helping to move the bowels.

Research is finding that insoluble fiber can cause more harm than good in people with a hypersensitive gut because this type of fiber tends to cause fermentation. Fermentation can lead to bloating and gas causing pain in people with IBS. Soluble fiber has been found to ease constipation and therefore be more beneficial.

FODMAPs (Sugar)

There also are several types of food items that can cause additional problems in people with IBS. Recent research has collected a set of sugars, called FODMAPs. This is an acronym for Fermentable Oligosaccharides Disaccharides Monosaccharides and Polyols. FODMAPs include simple sugars like fructose (monosaccharide) and lactose (disaccharide) and more complex sugars like galactans (oligosaccharide). In addition, it includes sugar alcohols like those found in gum and sugar free candy and soda (polyol).

While a complete list of foods can be found online, it’s important to understand why these sugars can affect IBS symptoms and realize that one may not need to avoid all foods listed. These sugars cause an osmotic effect on the gut, drawing water into the gut causing diarrhea. In addition, these sugars cause bacterial fermentation in the large bowel.

Good bacteria exist in the gut for several reasons including maintaining an effective immune system and helping to digest nutrients that we are not able to. It is not believed that people with IBS have more bacteria (although some research shows possibly different bacteria) in the large intestine. However, people with IBS tend to be more sensitive to bowel wall distention, making the extra gas produced from the bacteria more painful.

It’s important to speak to your doctor or dietitian before beginning any restrictive or “elimination” diet.

Gluten Sensitivity

Finally, we have reached one of the hot topics of the day: Gluten Sensitivity.

It’s important to first make the distinction between gluten sensitivity and Celiac Disease.

Celiac Disease is a specific autoimmune response that occurs in the gut in the presence of gluten. Celiac Disease occurs at birth, but may not be noticed until later in life. It results in “intestinal permeability” which allows bacteria and food protein to enter the blood stream. In addition, it leads to inflammation of the intestinal villi and can cause long term malabsorptive disorders if not treated.

Gluten sensitivity, on the other hand, is a non-specific immune response (innate immunity) that can occur hours or even days after the ingestion of gluten. It does not result in “intestinal permeability”, nor does it affect the intestinal villi. It is solely symptom based (like IBS), and can cause extra intestinal symptoms like brain fog or fatigue. It is difficult to diagnose because the symptoms can be very similar to IBS flares. In addition, people with a hypersensitive gut, like that of IBS, may find that small amounts of inflammation exacerbate their symptoms greatly.

In order to determine if gluten sensitivity is causing symptoms, it is recommended that the person go on a gluten free diet for 2-4 weeks. Common gluten containing foods include wheat, barley (including beer), rye, commercially available oats, jelly or jam, gravy, canned soups or broth, scalloped or boxed potato product, salad dressings, and licorice.

Gluten sensitivity is a common topic in the news and in research today. However, keep an open mind and remain objective. If a gluten free diet does not reduce symptoms, you may not have sensitivity at all. In addition, talk to your doctor or dietitian before beginning an “elimination” or overly restrictive diet.

Erin Slater, RD LDN

Drossman Gastroenterology Guest Blogger Erin Slater, RD LDN is a Registered Dietitian, with an interest in Functional GI Disorders. She is the Clinical Dietitian at Union Memorial Hospital in Elkridge, Maryland.