The She's All That star made her big screen debut at the age of 15 in 1995's The Babysitter's Club, and Cook admits she over-indulged in the free food on set.
The 31 year old reveals her self-esteem reached an all-time low when her weight ballooned and she "went too far in the other direction" as she strived to slim down.
She tells Fox News, "I remember gaining quite a bit of weight on the first movie that I worked on because, 'Hey, free food!'. You're at that stage where your body is just changing so actively, so it was a natural change, but I remember finishing that film and realising that I had gained probably 10 pounds over the course of filming which is a lot when you're only 5ft 2in.
"I knew then that I needed to go and really try and get healthy. I went too far in the other direction and I worried my parents for a while, I think it's fair to say. I think that it's something that many, many teenage girls go through, especially ones that are achievers and ambitious. You're looking for a sense of control, and when you're in a really transitional phase in your teenage years, I think it's a pretty normal reaction to develop food issues."