Sarah wears a helmet outside to protect her from falls

Sarah Laslett's diet includes cream, butter, nuts and eggs and is devised by Great Ormond Street Children's Hospital in London.

As Sarah burns off the fat her body produces ketones which protect the brain against seizures.

Sarah, from Morval near Looe, no longer suffers scores of blackouts and seizures every day.

The youngster has Myoclomic Astatic epilepsy, a rare, drug-resistant form of epilepsy that triggers scores of blackouts and seizures every day.

Her exuberance is wonderful and she has been completely transformed

Teacher Sonia Barrett

The attacks started eight months ago and meant Sarah had to wear a helmet when she was playing.

Then her family found out about a trial at Great Ormond Street of the ketogenic diet.

The high fat, low carboydrate, low protein diet is so finely balanced it has to be carefully calculated by experts who are on hand for advice and support.

One of the key features is restrictions on high-sugar foods, breads, pasta, cereal and starchy vegetables.

Mealtimes are a well-practiced routine of measuring food to within a gramme.

Water regulated

For instance, breakfast could consist of 25 grammes of cream, mixed with water, 43 grammes of egg, mixed with another 25 grammes of cream and 15 grammes of butter, followed by 21 grammes of fruit.

Different types of fruit have different carbohydrate levels so that too has to be adjusted.

Sarah also drinks a carefully regulated 120 millilitres of water an hour, to keep her hydrated, but also to avoid constipation and kidney stones.

Teacher Sonia Barrett has been looking after her at school since she became ill last September.

It has been 24 days since Sarah's last blackout but she still wears a helmet to play outside - just in case the fits return.

£25,000 raised

Ms Barrett said: "Only four weeks ago she would just sit very still. There was no animation and she seemed very sleepy a lot of the time.

"Now she is full of life. Her exuberance is wonderful and she has been completely transformed."

Sarah's family has also raised £25,000 to continue a trial at the hospital for another year and help other children like Sarah.

Her mother Alex said: "It's brilliant because other children now hopefully will get the same chance that Sarah's had to do this diet.

"I couldn't believe how a diet could make such a dramatic difference but for Sarah, this has been a miracle."

Great Ormond Street is recruiting children with severe epilepsy for the trial, although patients will need a referral from their paediatric consultant.