Kristin Cavallari is ''super committed'' to her fitness regime.

The 27-year-old beauty - who gave birth to her second son with her husband Jay Cutler just five months ago - is now said to be even ''tinier'' than her pre-pregnancy figure, according to her Pilates instructor Angie Mitchell.

Angie told PEOPLE magazine: ''She might actually be tinier [than her pre-baby weight]. She looks amazing.

''The reason why she wanted to actually start doing Pilates was because she had heard that she could continue to do it throughout her pregnancy, and then also to get her body back after she has a baby.''

To maintain her impeccable physique, the former 'The Hills' star does two 55-minute pilates sessions and one personal training session for strength-training per week and is said to be ''very conscious'' about her diet.

Angie continued: ''She's very conscious about what she puts in her body, and she's super committed [to her workouts]. She doesn't cancel and she likes to work hard, so she puts the time and the effort in. She's very consistent and she's very motivated and driven.''

Offering her advice to other new mothers looking to regain their fitness, Angie added: ''It's a process. You have to put in the time and the effort.''