New mother Katie Holmes has sparked fears for her health after shedding an astonishing 28 pounds since giving birth to baby Suri on 18 April (06).

The actress' strict diet and exercise regime has been slammed by health experts who insist she should be losing weight more leisurely.

But pals of the Batman Begins star reveal she's desperate to regain her pre-pregnancy figure before marrying Tom Cruise and will keep pushing herself until she's back to her svelte former self.

A friend tells British tabloid the Daily Star, "Katie has embarked on a hardcore fitness regime and does 200 sit-ups a day, combined with two hours of cardio work before pilates.

"She has eaten healthily since giving birth but now her friends are worried she has dropped two dress sizes in too short a period of time.

"She is rushing around all of the time and is on hand for the baby 24 hours a day.

"Her weight is just rapidly falling off. It can't be good and has got to be very stressful."