For the best benefit of fiber you should stick between 30-50 grams a day (a little bit higher than the normally reccomended 20g most Americans get). Just make sure you're getting adequate water as well and you will have no issues. Those numbers are pulled from a few articles I read when I was working on setting up my mealplan and converting to semi-vegetarianism. At that amount you get the best gastrointestinal benefit, and best benefit for your heart. Anything over that and you can start hurting your system.