People with irritable bowel syndrome (IBS) frequently report that their symptoms worsen after meals and believe they have food intolerances (true food allergies in IBS are uncommon). Some think that dairy foods or wheat and other grains are the culprits. Others say that spicy or fatty foods, cruciferous vegetables (broccoli, cabbage, kale, etc.), chocolate, caffeine, alcohol, soda, or gum bring on symptoms. Generally, people with IBS may get some relief by avoiding foods that trigger symptoms (keeping a food diary helps identify them), eating smaller meals, and staying well hydrated.
If no clear triggers are identified, however, eliminating lactose-containing foods and beverages may be worth a try. Some people with IBS are gluten-sensitive without having celiac disease, and going gluten-free may reduce their symptoms, possibly relating to improvements in gut permeability issues, though this has not been adequately studied. Before going on a gluten-free diet, a blood test should be done to exclude celiac disease.
Reviews for fiber are mixed; it may help overall, according to some (but not all) studies—especially soluble fiber (as found in psyllium) and especially in people with constipation-predominant IBS. But other studies have found no benefits of fiber over a placebo, and some IBS sufferers find that fiber, notably insoluble fiber like wheat bran, makes things worse. If you increase fiber, do so gradually to assess your tolerance, and drink plenty of water.
Figuring out FODMAP
One diet that has been meriting a lot of attention in recent years is “low FODMAP,” developed at Monash University in Australia more than a decade ago and now increasingly used in clinical settings in the U.S. The acronym stands for “fermentable oligosaccharides, disaccharides, monosaccharides, and polyols.”
These short-chain, highly fermentable, and poorly absorbed carbohydrates are found in a surprisingly wide range of foods, including some dairy products, wheat, rye, onions, cashews, apricots, pears, asparagus, apples, watermelon, mushrooms, cauliflower, legumes (like kidney beans), honey, agave, and sugar alcohols like sorbitol and mannitol.
Restricting FODMAPs, and carbohydrates in general, may alter the gut microbiome and lead to less gas and fluid accumulation in the intestines, thereby reducing bloating and pain in IBS. In contrast, some people without IBS may experience normal gassiness after consuming FODMAP foods, but not the pain and other distressing symptoms of IBS.
Low-FODMAP diets “show promise,” according to a 2014 monograph from the American College of Gastroenterology, while a 2017 review paper in Gut concluded that there’s “convincing evidence” for them—with about 50 to 80 percent of people with IBS having a good response.
Here’s a sampling of the research:
- One of the first randomized controlled trials, published in Gastroenterology in 2014, found that a low-FODMAP diet improved IBS symptoms over three weeks, compared to a typical Australian diet.
- A 2017 study in Gut similarly found that a low-FODMAP diet improved symptoms over three weeks, while a high-FODMAP diet had no effect or worsened symptoms in most subjects. It also found that the low-FODMAP diet was associated with reduced levels of the urinary metabolite histamine, which is thought to be involved in IBS.
- In a study in Gastroenterology in 2015, a low-FODMAP diet was as effective as traditional IBS dietary advice (to avoid large meals and reduce fat, caffeine, and gassy foods, for example).
- A 2017 study in Clinical Gastroenterology and Hepatology reported that the diet improved quality of life, among other benefits, compared with traditional IBS dietary advice.
Most of the FODMAP studies have been small and short-term—and there’s concern that this elimination diet could be risky over the long term, since it restricts many healthy foods and thus could lead to nutrient deficiencies or have other unintended consequences including possible adverse effects on the microbiome. Still, if you’ve been diagnosed with IBS and are up for the challenge, you can try the elimination phase of the diet for about three to four weeks to see if you feel better—after which you gradually reintroduce food groups (the challenge phase) to pinpoint which ones may be the triggers. From there, a maintenance diet would include FODMAP foods that are well tolerated.
An app developed at Monash University and regularly updated includes a large database of foods rated by their FODMAP content. A good web resource is FODMAPeveryday.com, which provides low-FODMAP recipes certified by Monash, along with other helpful information from IBS experts. But because the diet is so restrictive and hard to follow, it’s best done under the guidance of a registered dietitian nutritionist (RDN) who is knowledgeable about the diet and can ensure that it’s done in a healthful fashion.
Buyer beware: There is a budding industry of “low FODMAP” packaged foods, including snack bars and nutritional drinks, with manufacturers capitalizing on the large numbers of consumers who have IBS—or just suspect they have it. Some products are certified as “low FODMAP” by Monash University. But as with “gluten-free” foods, these foods are not likely to be of benefit if you don’t have IBS, and may even be harmful in some ways, as noted above. Beware also of unsubstantiated claims that a low-FODMAP diet will help you lose weight or have other health benefits.