The ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet primarily used to treat difficult-to-control (refractory) epilepsy in children.
The diet mimics aspects of starvation by forcing the body to burn fats rather than carbohydrates. Normally, the carbohydrates contained in food are converted into glucose, which is then transported around the body and is particularly important in fuelling brain function. However, if there is very little carbohydrate in the diet, the liver converts fat into fatty acids and ketone bodies.
The ketone bodies pass into the brain and replace glucose as an energy source. An elevated level of ketone bodies in the blood, a state known as ketosis, leads to a reduction in the frequency of epileptic seizures.
The diet provides just enough protein for body growth and repair, and sufficient calories to maintain the correct weight for age and height. The classic ketogenic diet contains a 4:1 ratio by weight of fat to combined protein and carbohydrate. This is achieved by excluding high-carbohydrate foods such as starchy fruits and vegetables, bread, pasta, grains and sugar, while increasing the consumption of foods high in fat such as cream and butter.
Most dietary fat is made of molecules called long-chain triglycerides (LCTs). However, medium-chain triglycerides (MCTs)—made from fatty acids with shorter carbon chains than LCTs—are more ketogenic. A variant of the diet known as the MCT ketogenic diet uses a form of coconut oil, which is rich in MCTs, to provide around half the calories. As less overall fat is needed in this variant of the diet, a greater proportion of carbohydrate and protein can be consumed, allowing a greater variety of food choices.
Developed in the 1920s, the ketogenic diet was widely used into the next decade, but its popularity waned with the introduction of effective anticonvulsant drugs. In the mid 1990s, Hollywood producer Jim Abrahams, whose son’s severe epilepsy was effectively controlled by the diet, created the Charlie Foundation to promote it.
The diet is effective in half of the patients who try it, and very effective in one third of patients. In 2008, a randomised controlled trial showed a clear benefit for treating refractory epilepsy in children with the ketogenic diet.