Starting a Low-FODMAP diet: What you need to know

If you’re a nutrition nerd like me, you might be familiar with the word FODMAP, which stands for “fermentable oligosaccharides, disaccharides, monosaccharides, and polyols.” FODMAPs are a group of carbohydrates that are often poorly digested in the intestine and, when fermented by bacteria that live in the gut, can cause a host of digestive woes.

While all people appear to poorly break down certain FODMAPs, some people are particularly sensitive: those who have irritable bowel syndrome (IBS) and those who have small intestinal bacterial overgrowth (SIBO).

IBS is a functional gastrointestinal disorder that is often identified once other, more severe conditions have been ruled out. The most common symptoms of IBS include lower abdominal pain, bloating, excessive gas, and diarrhea and/or constipation.

SIBO is a condition in which an overgrowth of bacteria from the large intestine moves up into the small intestine. Symptoms of SIBO can be very similar to those of IBS, so it’s important to work with your physician to determine the root cause.

You can test for the malabsorption of a few specific FODMAPs: fructose (a monosaccharide), lactose (a disaccharide), and sorbitol (a polyol). The test involves drinking a measured volume of one of these carbohydrates and later blowing into a tube attached to a special bag. If your body is unable to absorb that carbohydrate, intestinal bacteria will ferment it, producing gasses that are carried from the intestine to the bloodstream to the lungs, where they are exhaled into the test bag.

While there are currently no tests to confirm malabsorption of other FODMAPs, this is an area of intense research so more tests and information might become available in the future.

If you have the benefit of these test results, you can refine your approach to the low-FODMAP diet. For example, if you learn that you can absorb lactose without any issues, you can proceed with the low-FODMAP diet but not restrict lactose-containing foods such as milk and cheese. However, if you are not able to do the test, following the full low-FODMAP diet is recommended.

The low FODMAP diet has two phases. The first phase is a strict elimination of high FODMAP foods for anywhere from 2 to 6 weeks (though some dietitians recommend completing a full 8 weeks on the low-FODMAP diet). The purpose of this phase is to observe whether your symptoms are relieved when these potential triggers are removed. If this is the case, you would move on to the second phase of the diet.

The second phase carefully and systematically reintroduces specific FODMAPs back into the diet. It’s important to do this one by one, and in gradually increasing amounts, so you can pinpoint the specific foods (and amounts) of foods you can and cannot tolerate without symptoms. These triggers vary from one individual to the next.

Working with a knowledgeable registered dietitian and physician is key here, as determining whether you have sensitivities to certain foods (or certain amounts of specific foods) can be quite complex. To find a registered dietitian in your area, go to eatright.org.

The following list gives you a glimpse of high-FODMAP and low-FODMAP foods, but there are many, many others. For a comprehensive guide, visit Monash University or Low FODMAP Central.

High FODMAP Foods:

  • Breads and cereals: Crackers, cookies, and pasta made from wheat or rye
  • Dairy and alternatives: Milk, yogurt, ice cream, custard or pudding made from cows or sheep, cottage cheese, mascarpone, ricotta
  • Protein sources: Baked beans, chickpeas, kidney beans, lentils, soy beans
  • Vegetables: Artichokes, asparagus, broccoli, Brussels sprouts, cabbage, cauliflower, green bell peppers, eggplant, fennel, garlic, leek, mushrooms, okra, onion, scallions, shallots, sweet corn
  • Fruits: Apple, apricot, avocado, blackberry, cherry, lychee, mango, nectarine, peach, pear, plum, prune, canned fruit in natural juice, watermelon, fruit juices
  • Nuts and seeds: Pistachio, almonds (>10), cashews
  • Sweeteners: Fructose, high-fructose corn syrup, honey, corn syrup, sorbitol, mannitol, isomalt, maltitol, xylitol

Low FODMAP Foods:

  • Breads and cereals: Gluten-free bread or cereal products, 100% spelt bread, rice, oats, polenta, arrowroot, millet, quinoa, tapioca
  • Dairy and alternatives: Lactose-free milk or yogurt, oat milk, rice milk, soy milk, hard cheeses, brie, camembert
  • Protein sources: Tofu, tempeh, meats, fish, chicken, eggs
  • Vegetables: Alfalfa, bok choy, carrot, celery, endive, ginger, green beans, herbs, lettuce, olives, parsnip, potato, pumpkin, red bell pepper, spinach, sweet potato, tomato, turnip, zucchini
  • Fruits: Banana, blueberries, boysenberry, cantaloupe, grapes, grapefruit, oranges, raspberry, strawberry
  • Nuts and seeds: Almonds (<10), macadamias, walnuts, pumpkin seeds
  • Sweeteners: Sugar, glucose, maple syrup, molasses, artificial sweeteners that don’t end in -ol