Jessica Simpson has hired celebrity trainer Tracy Anderson to get her into shape.

The singer-and-actress - whose weight has fluctuated over the years - wants to look her best for when she marries fiance Eric Johnson later this year so has enlisted the help of Tracy and is already seeing results.

A source told Us Weekly magazine: "She wants to look healthy. She's seeing results. She really loves it. She thinks it's so much fun."

Tracy has previously worked with Madonna and Nicole Richie and is responsible for Gwyneth Paltrow's amazing post-children body.

Jessica has been keen to get fit for a long time and last year she took up boxing as part of a new fitness regime.

She wrote on her twitter page: "Just done boxing... second day in a row... Have I lost my marbles?"

In 2009 Jessica was pictured looking curvier than usual and sister Ashlee leapt to her defence after critics targeted her about her weight gain.

She said: "I am completely disgusted. Since when did a woman's weight become newsworthy? How can we expect teenage girls to love and respect themselves in an environment where we criticise a size two figure?"