A keto diet sources energy from fat instead of traditionally preferred carbs. By reducing carb intake and increasing fat cals, the body will “run out” of carbs & “switch” to fat. When fat is burned it creates ketones, which it can use for fuel. So basically, a diet high in fat & protein but very low in carbs is called a ketogenic or “keto” diet. Keto diets are promoted as being closer to Carbs: 5-10%, Fat: 65-75%, Protein 20%. Due to fact that most people on a keto diet are aiming to lose body fat (the reason for going into ketosis), their daily caloric intake is reduced to 1500kcals, supposedly putting them in a caloric deficit.