Emily Strunk, also known as "McRunnerette" plans to eat McDonald's for every meal for 31 days.
The fast food diet will end on Oct. 9, which is the day of the race.
Strunk, 36, said she is not worried about the calories or nutrition. She is concerned with being able to make it to the restaurant every time hunger strikes.
"My biggest concern is the logistics of it - getting to McDonald's enough during the day. I don't eat three meals a day. I kind of eat all day long," said Strunk.
Strunk is running to raise money for the Ronald McDonald house. It's a cause close to her heart. When trunk was 13 years old, her brother died of brain cancer.