In an interview with Into the Gloss the fitness guru revealed when the pair first met the now 40-year-old had a few "problem areas."
"She had 35 extra pounds on her. Her butt was long and she had outer thigh problems," she said. "Gwyneth is lucky because she's really tall, so she can hide it really well in clothes."
The extra weight was, of course, because the star had just had son Moses. So the trainer whipped the mom-of-two into superhero shape just in time for the first Iron Man flick to begin filming.