The word 'as' should not be in the sentence.
If it must be in the sentence, it would be:
A few of the athletes who were not as worried about their weight as (..........insert a noun here..... ) would sometimes order calorie-laden desserts every now and then.
Alternatively, instead if adding a noun, you could make it:
A few of the athletes who were not as worried about their weight as they should have beenwould sometimes order calorie-laden desserts every now and then.
Hope this helps!
