Since their introduction in 1921, high-fat, low-carbohydrate "ketogenic" diets have been used worldwide for refractory childhood epilepsy. Approximately half of the children have at least half their seizures reduced, including 15% who are seizure free. The mechanisms of action of dietary therapies are under active investigation and appear to involve mitochondria. Once perceived as a last resort, modifications to initiation and maintenance, as well as the widespread use of pre-made ketogenic formulas have allowed dietary treatment to be used earlier in the course of epilepsy. For infantile spasms (West syndrome) specifically, the ketogenic diet is successful about 50% of the time as a first-line treatment. New "alternative" diets such as the modified Atkins diet were created in 2003 and can be started more easily and are less restrictive. They may have particular value for countries in Asia. Side effects include constipation, dyslipidemia, growth slowing, acidosis, and kidney stones. Additionally, neurologists are studying ketogenic diets for conditions other than epilepsy, including Alzheimer's disease, autism, and brain tumors.