No one knows exactly how or why the diet works, but it has been found to be as effective - if not more so - as the new generation of antiepileptic drugs in controlling refractory (recurrent) seizures. In one study, at least half of all the patients treated with the ketogenic diet had their seizure frequency cut in half (Epilepsy Curr, 2004; 4: 215-22). It seems to be especially effective in controlling childhood seizures, generally well tolerated and rarely associated with side-effects (J Paediatr Child Health, 2005; 41: 353-7).
Initially developed at Johns Hopkins in Baltimore, Maryland, in 1921 to mimic the anticonvulsant effects of fasting - which can also prevent seizures - the ketogenic diet involves radical nutritional changes. The classical ketogenic diet has a fat-to-carbohydrate ratio of 4:1. The amount of protein is restricted so that fat accounts for around 90 per cent of calories, and the intake of carbohydrates is also restricted. (Children are usually limited to eating only 75 per cent of the recommended daily allowance for their height and weight.)
For a more complete description of the ketogenic diet, consult WDDTY vol 6 no 11 (Comment).