Even meticulous measuring can be corrupted by a fat brain. A couple of years ago I realized that an extremely fat family member thought grams and ounces were the same t  58e9  hing.  So if a serving of potato chips was 160 calories for 28 grams, she'd measure out 5 ounces in a mixing bowl and proclaim that she was only eating 40 calories worth of chips.  Nothing I said or did could convince her that there are approximately 28 grams in an ounce and that she was really eating 800 calories in a single "snack."