Gosh! My next marathon is already in two weeks! Year after year, I'm trying to grab some good advices from runners to improve my preparation. The aim is to constitute my own rules to improve my experience in running.

One of them is about sugar. Let me explain it in brief.
I'm not a nutritionist, but I'm trying to understand how the body operates.

When you are running you need sugar, particularly fast sugar, which could be directly used by the muscles; the body likes to have habits.
Two weeks before the race, one of the trick is to reduce the most part of the sugar you are eating every day[1]. It has to be done during one week. This will create a need of sugar in your body. The last week before the race, do the contrary and eat high sugar food; and you will have better stock of fast sugar the day of the race.
Therefore, the second week, the body will make a lot of sugar stock because of the first week to be able to face another period of sugar lack.

It isn't as easy as we could think, even just for one week! Perhaps it's the hardest part of the preparation.

Notes

[1] like starch