The keto diet is a high-fat, low-carbohydrate diet that puts the body into a metabolic state called ketosis. It was originally developed in the 1920s as a medical treatment for epilepsy in children. On keto, the body burns fat for fuel instead of glucose, producing ketones that can reduce seizures. While other low-carb diets eventually reintroduce carbs, keto is much higher in fat and limits both carbs and protein. People follow keto for potential weight loss and health benefits like reduced disease risk, though long-term safety research is still emerging.