When you starve yourself, your body tries to use fat as an exclusive energy source. You can do it in the short term, but your body loses all or most stored carbohydrate within the first day. Then energy needs of some organs and tissues that critically need glucose are met by breaking down muscle protein and using the liberated amino acids to synthesize the necessary glucose.
If you exercise, your muscles will start using fat breakdown products nearly exclusively to meet its energy needs. This spares glucose for the brain and other tissues not able to shift quickly to fat breakdown products. Gradually, nearly all tissues will move over to using fat breakdown products to meet energy needs and thus spare the glucose synthesized from skeletal muscle breakdown—allowing the glucose to be utilized nearly exclusively by the brain and the kidneys, and eventually only the brain. In true starvation even the brain will eventually go over to using fat breakdown products as the continuing breakdown of skeletal muscle will endanger and weaken posture.
Actually, about 10 days into a starvation diet the extensive breakdown of fat will begin to simulate the metabolic conditions in diabetes. Indeed, after about 8-10 days you might pass out in the shower and be mistaken for a diabetic about to go into a coma. Certainly, no one wants to induce this condition deliberately, even though it may cause you to lose weight initially at a prodigious clip. Your body will recognize what you are doing and will slow down your metabolism. You will be too weak to exercise vigorously and you will start to thus slow or cancel out subsequent weight loss.
Indeed, if you can’t exercise but continue to starve yourself, your body will not only break down fat but will also start to re-synthesize it. This re-synthesized fat won’t wind up entirely back in fat tissue, but some will be stored in elsewhere, mostly in the liver. This isn’t a permanent condition. Still, it shows that a more sensible strategy would be to lose excess weight slowly and not use the liver as a way-station for the fat you need to eliminate.
It’s also beneficial to try to avoid excessive breakdown of skeletal muscle by starving yourself, but rather go more slowly and rebuild muscle as you go along with exercise and by increasing the relative amount of protein in the diet.
These are problems that attend starvation, which can be completely avoided by shooting for losing about 1-2 pounds a week instead of 4-5 or more. Don’t try to go at break-neck speed and crash-land into your final goal a few months later. It’s not worth it. Take your time.
Rather, reduce calorie intake slowly. A reduction of about 500-600 calories per day will yield about 1 pound per week. An average of about 1 pound per week will result in the loss of those 100 pounds in about 2 years. In truth, you may lose 1-2 pounds per week initially and then less, until you get to maybe 1-2 pounds per month as you ease into your final goal.
Over the course of a year or two you’ll become accustomed over that longer period to a new body and a new way of life, having put your body under far less stress in the interim.
