1. a diet that supplies large amounts of fats, moderate amounts of proteins, and minimal amounts of carbohydrates and that is undertaken for weight loss or to control seizures in treatment-resistant epilepsy Note: As the body is deprived of carbohydrates in the ketogenic diet, insulin secretion drops and glycogen stores in the body become depleted. The body then enters a state of nutritional ketosis where ketone bodies formed by the metabolism of fatty acids replace glucose as the primary energy source.
A ketogenic diet, says [Robert] Atkins, burns one's fat stores and uses them as a source of fuel.
— Lisa Teresi Harris The keto diet can be restrictive and requires that you carefully measure out the various macronutrients—fat, protein and carbohydrates—to keep your body in ketosis and gain the benefits of the diet.
— Elaine K. Howley The center offers the latest medical and surgical treatments as well as the ketogenic diet—a special high-fat, low-carbohydrate diet that helps control seizures in some people.
— The New York Times Magazine

2. a diet supplying a large amount of fat and minimal amounts of carbohydrate and protein and used especially formerly in epilepsy to produce a ketosis and alter the degree of bodily alkalinity