A 2004 study found that the ketogenic diet is used at 80 U.S. centers and at 70 centers in 41 countries. Continued use in patients has ranged from 1 to 45 years, with a median of 8 years. The average number of people per country using the diet was 71.6, with 5.4 started per year, in a range of 0 to 40 (Epilepsia 2004;45:1163).