Understanding FODMAPs

Perhaps it was a dinner with asparagus and apple pie that left you feeling bloated and miserable. Or maybe it was that pasta salad you had for lunch, the slice of watermelon that tasted like summer or the margarita you enjoyed at a Mexican restaurant. In all cases, your discomfort came on quickly and was followed by an urgent need to empty your bowels. After a quick trip to the bathroom, the incident was over.

Sugar in a teaspoon and pored on a table
chokja / iStockphoto

The foods that caused your bowel distress may seem unrelated, but they have one element in common. All contain short-chain carbohydrates that can ferment in the digestive tract, causing bloating, gas, abdominal pain, constipation, or watery diarrhea in people with irritable bowel syndrome (IBS) and other functional gastrointestinal disorders.

Such foods are known as FODMAPs, an acronym that stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. “FODMAPs” may sound funny, but the symptoms these foods cause are no laughing matter. The good news is that a low-FODMAP diet can help alleviate such symptoms.

Why FODMAPs Cause Discomfort

As stated above, FODMAPs are short-chain carbohydrates. When the enzymes necessary to break down these foods are absent or lacking—or the transporters necessary to carry the nutrients across the intestinal walls are not fully functional—the sugars are poorly absorbed and remain in the gut. This can result in increased water flow in the intestinal tract and rapid fermentation by gut bacteria.

As a result, the intestine becomes distended by the extra water and the gas that is produced, which can result in bloating and pain in as little as 30 minutes. This is often accompanied by an urgent need to have a bowel movement, which can relieve symptoms.

Take fructose, for example. It is found freely in foods and is a component of sucrose (table sugar). Fructose is absorbed in the small intestine through two transporters. The one that takes up only fructose has a low capacity. The other, more efficient one shows up only when glucose is present. When there is more fructose than glucose in the gut, the fructose is poorly absorbed, causing IBS symptoms. When the ratio of glucose to fructose is higher, both carbohydrates are pretty well absorbed.

Polyols are different, however. Polyols are not well absorbed in the small intestine. When they reach the large intestine, they may cross the internal lining through pores. Certain diseases can diminish pore size, making it difficult to absorb polyols. As they ferment, polyols attract fluid to the small intestine, causing watery diarrhea.

A Quick Look at the Role of Stress

Stress plays a big role in IBS. Although the symptoms can begin at any time in life, they commonly appear in the stressful teenage and college years and then continue throughout adulthood. Additionally, women with IBS tend to experience constipation, whereas men with IBS are more likely to have diarrhea.

Many people with IBS find that FODMAPs only cause symptoms when they react to stress by feeling anxious or depressed. Moreover, research has shown that hypnosis can be as effective as FODMAP avoidance in preventing symptoms from occurring.

Taking Control of Your Diet

The frustrating thing about IBS is that there is no rhyme or reason as to which FODMAPs produce symptoms. That’s why it is necessary to eliminate all FODMAPs for a minimum of two weeks—three weeks is preferred. This allows the gut to rest and recover.

After two weeks, you begin challenging your gut by reintroducing one FODMAP at a time. If the food is going to cause symptoms, it will happen fairly quickly. Within a few weeks, you should know which FODMAPs, and in what amount, trigger your symptoms—these are foods you should avoid. There will be no need to avoid eating FODMAPs that don’t cause symptoms, as they are part of a nutritious, balanced diet. 

So, in the first phase of the FODMAP challenge diet, you need to eliminate all FODMAPS entirely. Despite the large number of foods that you must avoid during the elimination phase, there are still plenty of FODMAP-free foods to enjoy! 

Special note about fruit though. Some fruits contain as much as or more glucose than fructose. This means that people with IBS can often tolerate them in small amounts. They should be eliminated in the first phase of the FODMAP challenge, however, but may be eaten carefully later. 

Why people react to some FODMAPs and not others is unknown. It is also not always clear why some people can consume small amounts of a FODMAP without experiencing symptoms. What is clear is that eliminating FODMAPs for two or three weeks, then reintroducing them one-by-one, usually reveals the offending foods.

By avoiding such foods, about 70 percent of people with IBS find their symptoms disappear completely. If you are one of the 30 percent who does not achieve success with this diet, see a dietitian for advice. A dietitian often needs to be involved in the FODMAP challenge to be successful.

Once you figure out which foods are causing your symptoms, avoiding these foods should become routine. Often, this means eliminating processed foods, since FODMAPs hide in many manufactured foods in the form of thickeners and preservatives. If you eat whole foods and foods you prepare yourself, you will be able to manage well.

As you eliminate the foods that offend your gut, you should add high-FODMAP foods that you can tolerate back into your diet. Eating a wide variety of these foods encourages a diversity of intestinal bacteria that keep your gut healthy. For a happy gut, just limit the foods necessary to avoid symptoms.

Dr. Cresci works in pediatric gastroenterology at Cleveland Clinic's Lerner Research Institute, and develops clinical nutrition research for the Center for Human Nutrition.

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