Why was Regina George on a all carb diet

She really wanted to lose 3 pounds!

I don't understand why the KAL-Teen bars are supposed to make her gain weight but she eats like a bear all the time anyway, so what was the point of the bars and why did she eat so much in the 2nd half of the film?

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Love means never having to say you're ugly. - The Abominable Dr. Phibes

It's because carbohydrates are supposed to give you energy by breaking down the salt into sugar and the sugar into fuel. Cady had lied saying that the Kal teen bars burn up all the carbs, so maybe Regina was eating mass amounts of food to make up for a supposed lack of carbs, when really she was being sabotaged and inadvertently gaining extra weight.

I thought a carb diet means she avoids carbs