There was a time (late 70's and probably earlier) where the 'depletion phase' of carbohydrate loading before a marathon was 'the thing to do'. This involved cutting carbs for a few days and then doing a long run to deplete most/all of your glycogen reserves. Then, supposedly, when you added carbs back to your diet your body would over-compensate and store more glycogen than normal. Kind of like 'running up to the edge of a bonk'.

AFAIK, this is no longer considered to be effective.

dave