Why some girls work out a lot but their stomach still looks awful?

I know quite a few girls who do crunches on a regular basis or go to the gym a lot, but they still have a huge gut. I was just wondering why? I even know one girl who felt better about herself for doing crunches, but I swear she looked bigger than she had when I last saw her. I know a girl who works out all the time at two gyms and she still can't lose tummy weight. What's up with that?
Why some girls work out a lot but their stomach still looks awful?
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