The article explains that fasting is often prohibited by malnutrition and low body weight. Obviously fasting cannot be undertaken long-term, as it results in starvation. I wonder whether there is any benefit to caloric restriction / fasting, versus maintenance calorie intake with a ketogenic diet. The crucial thing seems to be the elimination of insulin promoting carbohydrate, and depletion of glycogen which forces metabolism into ketogenesis, reduces growth factors, and promotes catabolism and autophagy.