Katie Holmes is on an "extreme purification" detox to prepare for pregnancy.

Katie is reportedly following Scientology's controversial Purification Rundown programme - an extreme detox process which has left her looking fragile and weak.

Katie is believed to be doing the detox - which involves spending long periods in a sauna every day - in a bid to conceive her second child with her husband, Scientologist Tom Cruise.

A source told Britain's Daily Star newspaper: "She is undergoing an extreme purification programme so she is toxin free when she and Tom try for their next baby."

Katie - who has a two-year-old daughter, Suri, with Tom - has missed a number of events, including the Oscars and New York Fashion Week, due to the toll of the detox.

Friends say she has been resting for days after the Purification Rundown left her exhausted.

According to the website scientologytoday.org, the Purification Rundown is "a carefully designed combination of exercise, vitamins, nutrition and sauna use which dislodges drug residues and other toxins from the fatty tissues".

It has been claimed the process involves taking 'vitamin bombs' and staying in saunas for up to five hours at a time to cleanse the body.