Kale is very high in fiber so it shouldn't back you up, though some people are a little fiber-sensitive. Have you been also eating things that are higher in iron? THAT can sometimes cause issues. Like Maezy said, salad will help add some roughage to your diet (and lettuce is free!), you can also look for sugar-free fiber supplements like Metamucil if you notice an ongoing problem with it. I've had C issues for a long time, Smooth move and some Colace usually clear that up for me