The original ketogenic diet is a high-fat, low-carbohydrate diet developed in the 1920s and used to treat drug-resistant childhood epilepsy. The fad diet that adopted the same name is also a high-fat, low-carb diet, but proclaims to induce weight loss. The premise of the weight-loss ketogenic diet is that if the body is deprived of glucose obtained from carbohydrate foods, it will produce energy from stored fat. A typical version of this keto diet for adults has about 50% of food by weight coming from fat (70% of calories).

A 2020 review looked at a very low carbohydrate ketogenic diet that was high in fat but low in protein. It found that it was an effective means for weight loss in those who are overweight or obese, yielding an average weight loss of 10 kg over four weeks, with maintenance of the weight loss for up to two years. However, concerns about serum sodium levels led the authors to propose the diet only be used in "selected" people, and under strict medica