Chrissie Augrandjean from Clacton, Essex, has glycogen storage disease, a metabolic disease so rare it affects just one in three million people.
Her liver is unable to release glucose, and the only treatment that works for the youngster is 250 grams of cornflour every single day.
Chrissie was just three years old when she was diagnosed, after hospital doctors found her liver enlarged by more than 2in.
Initially, she was fed via a nasal tube for three years, before she became fit enough to just have cornflour.
The powder is the white starch extract from maize kernels, and is more or less tasteless. In cooking, it is used as a thickener, and can be blended to a a smooth cream with liquid. Chrissie takes it with water, and it gives her a slow release of energy through the day.
Without it, Chrissie could get liver damage, or fall into a coma.
The Sun reports that devoted mum Jacqui has to set an alarm for 2am for one of Chrissie's doses.
She told reporters that her daughter is 'amazing' and 'doesn't ever complain'.
"She has even become a cornflour connoisseur and can tell which ones she likes and which ones make her feel ill," she said, adding: "It's just amazing how much of it she has to have every day but it means that she can live quite a normal life."
Chrissie said: "Some of the cornflour doses make me gag but I found the one that I like the best and just stick to that. I am just used to having to have it now and my friends are used to what I have to do. It sometimes gets a bit annoying but I guess I just get on with it."
The NHS allows the family to claim back the £22 they spend per month on the cornflour, as they deem it a legitimate treatment for her.
What an amazing use for such an innocuous store cupboard product!