We have been told forever that fiber is going to prevent cancer and keep our colon healthy. Unfortunately the evidence for this is only bias, fairytales and poor quality correlational epidemiology.
The only studies that show fiber is of any benefit are studies using food questionnaires. These questionnaires ask people what they had to eat over the last year or many years. How reliable is this data to begin with? Can you remember how many cups of broccoli you ate in the last year? I can’t remember what I ate last week let alone specific amounts over a year of a specific food. Also people lie. They want people to think they eat better than they do.
So these studies take all this data and they break the people up