Health campaigners have expressed concerns over a Channel 4 show encouraging women to go on crash diets.
Madrid Fashion Week recently banned underweight models
In Super-Skinny Me: The Race to Size Zero, several female journalists will try out various extreme diets.
The Eating Disorder Association said it had "very serious concerns" about the health of the women taking part.
But a spokesman for Channel 4 said: "This is a shock doc with a real sense of purpose." The programme is expected to be shown early next year.
"It provides the perfect opportunity to debunk the current clamour for all things super-skinny," the spokesman added.
Steve Bloomfield of the Eating Disorder Association, said there are "some potentially quite serious risks to the participants".
"It could be very difficult to eat normally again after this experiment is over," he added.
Extreme weight loss can lead to medical problems such as osteoporosis and it can also affect fertility.
"We are not going to condemn a programme we haven't seen but we would certainly like to see a very high level of close medical supervision for the participants," Mr Bloomfield said.
Channel 4 confirmed that medical support and guidance will be on hand for the volunteers, who will attempt to slim down to a size double zero - the US equivalent of a UK size 2.
The documentary will also examine the recent Hollywood trend for being ultra-thin.
The Spanish Association of Fashion Designers recently decided to ban models who had a BMI of less than 18 for Madrid Fashion Week.