Kossoff EH et al. (2007) When do seizures usually improve with the ketogenic diet? Epilepsia 49: 329–333

The ketogenic diet (KD) is a high-fat, low-protein and low-carbohydrate diet that can be implemented as a treatment for children with intractable epilepsy. Currently, there is a lack of published data regarding both the length of time required to achieve seizure improvement in children who are on the KD and the time after which improvement is unlikely to occur.

To address these issues, Kossoff et al. performed a retrospective chart review of children with intractable epilepsy (n = 118, age range 0.3–15 years) who were started on the KD at two US hospitals between November 2003 and December 2006. In total, 99 (84%) children showed seizure improvement while on the KD. Of these, 75% responded within 14 days of diet initiation, 90% within 23 days, and all within 65 days. In this study, if seizure improvement did not occur by 65 days, it did not happen at all. Of the children who did show seizure improvement, 76% either maintained or continued to improve upon the initial level of seizure reduction over 6 months. Notably, in the subset of children who responded to the KD, initial improvement was much quicker in those who fasted for 1–2 days before initiation of the diet than in those who did not (median 5 versus 14 days), although fasting did not affect seizure reduction in the long term.

The authors conclude that the KD usually works very quickly, and even more rapidly if started after a fasting period. Conversely, if seizure frequency in children does not improve within 2 months of initiation of the KD diet, this therapy is unlikely to be effective and other treatments should be considered.