The reason onions can make matters worse for IBD patients is that they’re considered a high-FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) food. FODMAPs are sugars that can prompt unpleasant gastrointestinal symptoms like bloating, gas, or stomach pain, registered dietitian Anne-Marie Stelluti explains (via Crohn’s & Colitis Australia).
Additionally, if you’re experiencing diarrhea as a symptom during a Crohn’s disease flare-up, you’ll want to dial back your fiber intake, which means steering clear of raw veggies like onions. According to the U.S. Department of Agriculture (USDA), 1 cup of chopped raw onions contains 2.72 grams of fiber. While this isn’t an exorbitant amount, it’s recommended to hold off on eating too much fiber until after gastrointestinal symptoms have resolved.
Unfortunately, unions can be tricky to avoid as they’re often hiding in our favorite stews, cream sauces, dips, and more. For these reasons, people with IBD may benefit from sticking with a low-FODMAP diet.