Scientific studies of human caloric needs necessarily assume that we meet our “needs” if body weight does not change. If you lose weight, then you are eating less than your tissues demand (caloric restriction), or you are increasing how much they demand (insulin sensitivity), or both. Depending on what and when you eat, or how much and for how long you restrict your eating, weight loss can shift from reducing mostly body fat to reducing mostly lean tissue. Therefore, weight loss in itself is not a direct indication of health. We know that long-term caloric restriction of 10-40% can improve health as long as there is no malnourishment, but more than 50% caloric restriction ultimately risks organ system failure. Too much of what is good for you, or too little if less is good for you, is not necessarily good for you. We also know that a 100% restriction i.e. fasting, does not lead to immediate death, but is it healthy?