evidence: Oatmeal is a super-versatile food that many of us love to eat for breakfast, a snack, or even as a savory side dish. And while it's a great whole grain offering, oatmeal can be a problem if you have stomach issues, especially individuals with certain gastrointestinal issues like irritable bowel disease. One cup of oats contains a little over 8 grams of fiber. [...] But ultimately, it's about what you're putting in your oatmeal that can lead to the biggest problems. (Related: The Unhealthiest Way to Prepare Oatmeal, According to a Dietitian.) [...] But adding sugar isn't the only thing that can make your oatmeal unhealthy.