Broccoli, cauliflower, Brussels sprouts, and kale all fall under the category of cruciferous vegetables. These foods are high in a number of nutrients like folate, vitamin C, and fiber. They're even thought to help prevent cancer.But they also contain raffinose, a type of carbohydrate that our bodies can't break down because we lack a certain enzyme to do so. Instead, raffinose is fermented by bacteria, a primary cause of gas and bloating.If you don't want to give up these vegetables, try roasting or steaming them to make them easier to digest.