Dear Doctor:

I was recently diagnosed with irritable bowel syndrome and was told to follow something called the low-FODMAP diet. Honestly, this is all so new that it’s stressful and confusing. Can you explain what’s going on?

Dear Reader: First, you’re not alone in feeling overwhelmed by a new and unexpected diagnosis. Not only are you getting a crash course on an unfamiliar medical state or condition, you’re also being asked to master the details of a new treatment regimen. This can easily add to your stress.

Your diagnosis means that your medical history, along with the symptoms you’ve described to your health care provider, match those of a chronic disorder known as IBS, or irritable bowel syndrome. Symptoms typically include recurrent abdominal pain, which is accompanied by bloating, cramping, gas, constipation or diarrhea. Many people living with IBS find that episodes of diarrhea will alternate with periods of constipation. IBS is a chronic condition, which means that it is managed rather than cured. The cause is unknown. However, recent research points to a gut-brain connection.

Diet is a first line of defense in managing IBS. The FODMAP diet your doctor recommended is an acronym for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. The “ODMAP” of the acronym are certain sugars, contained in some foods. (Not all carbohydrates are considered FODMAPs.)

For people with IBS, foods with these types of sugars are either not completely digested or are incompletely absorbed. The sugars also cause the foods that contain them to be osmotic, which means that they attract water. These factors can cause these foods to be fermented — that’s the “F” in FODMAP — by bacteria in the digestive tract, leading to the gastric symptoms of IBS.

Foods to avoid include those with fructose, which means fruit, honey and anything made with high-fructose corn syrup. Stone fruits like peaches, nectarines, plums, cherries and apricots also contain polyols, a carbohydrate known as a sugar alcohol, which is directly referenced in the FODMAP acronym. Also, avoid dairy products that contain lactose. Low-lactose milk products such as aged cheeses and lactose-free yogurt are usually OK. Other high-FODMAP foods include wheat products, onions, garlic, lentils, beans and legumes, including soy and soy products. Some artificial sweeteners also contain polyols, and should be avoided.

Because each person’s body responds differently to specific high-FODMAP foods, the diet is broken into two phases. The first phase asks patients to eliminate all high-FODMAP foods from their diet for a period of four to six weeks. In the second phase, the eliminated foods are gradually reintroduced. This allows problem foods to be identified.

Fine-tuning the FODMAP diet so that it is varied, interesting, nutritious and high in fiber is challenging.

We suggest working with a registered dietitian nutritionist or certified nutritionist to craft a diet that is both effective and sustainable.