text: how long before carbs turn into fat? i am curious on how long it takes after eating simple carbs such as cereal, rice , bread, for it to turn to fat if not used . is it right away or does it take an hour or so of inactivity. carbs don't "turn" into fat.    carbs and all food are energy.  your body only needs a certain amount of energy so if you eat more "energy" than you need, it gets stored as body fat.  carbs are used for energy before anything else.  then protein, then dietary fat, then finally body fat.  if you eat too many carbs, then the protein & fat you're eating won't get used because they aren't needed.  if they aren't needed then your body won't use it's fat for energy because you already ate enough calories (energy).  look at it this way, if you weigh 200 pounds and need 2000 calories to stay that weight, then start eating 1000 calories your body will take 1000 calories from it's body fat to make up the difference.    you need to use 3500 calories to lose 1 pound, so after 3 days you would lose 1 pound.  unless you did the kimkins diet because it's thermogenic properties easily double that weight loss.