I agree with what Maria, Kim and Lynda say. And I would like to add that making healthy choices is a good thing as long as it's not an obsessive thing. And maybe if you change your wording a bit (saying "I don't want to eat cake now." Why? "Because I don't feel like it" instead of "I shouldn't eat cake", because that sounds like you put restrictions on yourself, instead of making a choice), your friends won't bother you as much about the food thingy.
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