they are referring to a detox diet or colonic cleanse. if you want lots of information (and graphic photos) google either term.

many athletes detox on a regular basis. I do it about 3 times a year (it's a ritual with me and seasonal changes: winter, spring, and summer). I'm in week two of a detox right now. I personally find the process uplifting and renewing but it's definitely not for everyone.

and I wouldn't consider it a fad diet. I also wouldn't suggest trying it without the guidance of either a doctor or a nutritionist.

there are lots of reasons to detox, but the primary one (in my opinion) is to improve liver function and remove the toxins from your body.