"Eating raw garlic may cause an upset stomach, with symptoms such as bloating, heartburn and gas in some people," says Ehsani. "It's also considered a high-FODMAP food, so may cause increased gastrointestinal distress or discomfort for people with IBS." On the other hand, garlic contains prebiotic fiber that in someone without IBS could improve gut health by feeding the good bacteria in the digestive system.