A recent publication suggests that children and adolescents following ketogenic diets exhibit an over 50% reduction in seizure frequency.
Following a 24 month ketogenic diet, studies have found clinically relevant improvements.
The ketogenic diets consists of a high fat (90%), low carb food consumption. As the liver oxidizes fats, they are metabolized into ketones bodies that are essential in seizure control.
For more information, see http://www.ncbi.nlm.nih.gov/pubmed/25518023