Katie Holmes looked even more gaunt and exhausted as she worked on the set of her new film last night.

Her painfully thin appearance has prompted fears about the effects of the extreme detox diet she is rumoured to be on.

Gaunt: Katie Holmes in New York

She has lost weight over recent months but in the last few weeks she has been photographed looking ever more tired and drawn. It has been speculated that Holmes, 30, is on the extreme diet to become "toxin-free" as she and husband Tom Cruise, 46, try for a brother or sister for Suri, two.

Yesterday the glumlooking actress was spotted trudging between scenes wearing jeans, a black overcoat, thick scarf and white beanie hat.

The script of The Extra man, being filmed in New York, is secret but it is believed to tell the story of a failed playwright who is an escort for rich widows.

Holmes is believed to be on the Purification Rundown, a controversial calorie-burning regime approved by the Church of Scientology, of which Cruise is a prominent member. Holmes was reportedly so exhausted by the punishing diet she was too weak to attend the Oscars ceremony.

Last weekend the couple were spotted at an Italian restaurant in LA with actor John Lithgow, with fellow diners noticing that Cruise was in a good mood, thanking the chef, but Holmes barely ate and looked miserable.

Despite suggestions that she is losing weight, Holmes says she enjoys nothing more than eating Cruise's cooking, telling Glamour magazine he makes pasta carbonara for her.