Well, he laid it out for her... "The error is in the counting, not in the fruit." ... and in the clips before that scene you hear her say everything you need to hear to understand her "counting error": "sometimes I'll buy a box of four and eat three of them (creme cakes)", " sometimes I'll eat a Mars bar before class, but I'll burn it off."  No, you won't burn it off.  You just ate half a day's worth of calories in a few bites and you are fucking worried about fruit!? Add up those sometimes creme cakes, and sometimes candy bars, and sometimes whatever other treats you aren't reporting and you have "most of the time" you're eating too many calories and expecting low-intensity belly-wobbling to correct the problem.