Epilepsy is one of the most common neurological disorders after stroke, and affects around 50 million people worldwide. It is diagnosed in a person having recurrent, unprovoked seizures. These occur when cortical neurons fire excessively, hypersynchronously, or both, leading to temporary disruption of normal brain function. This might affect, for example, the muscles, the senses, consciousness, or a combination. A seizure can be focal (confined to one part of the brain) or generalised (spread widely throughout the brain and leading to a loss of consciousness). Epilepsy can occur for a variety of reasons; some forms have been classified into epileptic syndromes, most of which begin in childhood. Epilepsy is considered refractory (not yielding to treatment) when two or three anticonvulsant drugs have failed to control it. About 60% of patients achieve control of their epilepsy with the first drug they use, whereas around 30% do not achieve control with drugs. When drugs fail, other options include epilepsy surgery, vagus nerve stimulation, and the ketogenic diet.
The first modern study of fasting as a treatment for epilepsy was in France in 1911. Twenty epilepsy patients of all ages were "detoxified" by consuming a low-calorie vegetarian diet, combined with periods of fasting and purging. Two benefited enormously, but most failed to maintain compliance with the imposed restrictions. The diet improved the patients' mental capabilities, in contrast to their medication, potassium bromide, which dulled the mind.
A Cochrane systematic review in 2018 found and analysed eleven randomized controlled trials of ketogenic diet in people with epilepsy for whom drugs failed to control their seizures. Six of the trials compared a group assigned to a ketogenic diet with a group not assigned to one. The other trials compared types of diets or ways of introducing them to make them more tolerable. In the largest trial of the ketogenic diet with a non-diet control, nearly 38% of the children and young people had half or fewer seizures with the diet compared 6% with the group not assigned to the diet. Two large trials of the Modified Atkins Diet compared to a non-diet control had similar results, with over 50% of children having half or fewer seizures with the diet compared to around 10% in the control group.
Because some cancer cells are inefficient in processing ketone bodies for energy, the ketogenic diet has also been suggested as a treatment for cancer. A 2018 review looked at the evidence from preclinical and clinical studies of ketogenic diets in cancer therapy. The clinical studies in humans are typically very small, with some providing weak evidence for anti-tumour effect, particularly for glioblastoma, but in other cancers and studies, no anti-tumour effect was seen. Taken together, results from preclinical studies, albeit sometimes contradictory, tend to support an anti-tumor effect rather than a pro-tumor effect of the KD for most solid cancers.