Here are some of the reasons diets don't work. First, no one can sacrifice forever. Caloric restriction, in and of itself, leads to binge-eating episodes. Second, low calorie diets produce tired, cranky people.
Third, and most importantly, low calorie diets utilize lean muscle as an energy source. Muscle cells contain many mitochondria, the fat burning machinery of cells; while fat cells contain very few mitochondria. Hence, muscle cells utilize many calories while fat cells utilize very few. The goal is to maximize muscle and minimize body fat. Unfortunately, the scale does not differentiate; i.e., the scale does not tell us how much of the weight is muscle versus fat. All diets focus on scale weight and are thus focusing on the "wrong" measure.
Again, All low calorie diets force the body to utilize muscle for energy. The scale weight decreases, but at what price? Precious fat burning machinery - muscle - is lost. The scale goes down but is destined to go right back up. When the weight is gained back it’s all fat. The only known method of permanent weight loss is exercise (both cardiovascular and muscle strengthening) and healthy eating. Eating healthy, along with muscle strengthening exercises, are critical to regaining that precious muscle.
Did you know your body needs carbs to burn fat? Your muscles use fat in conjunction with carbs. How much fat your muscles can utilize depends on how much muscle you have and how much oxygen reaches your muscles. So an aerobically fit person with lots of muscle burns much more fat than an aerobically unfit person. Your muscles store carbs for you. If your muscles run out of carbs they cannot utilize fat for energy—no matter how much fat is stored in your fat cells.
What does this mean for you? It means that you must eat to burn fat. A word of caution: your muscles can store only a finite amount of carbs, so it is much better to eat smaller portions and to eat more frequently during the day. Overeating at one meal forces the body to store (beyond what it can store in the muscle and liver) the excess carb calories as fat in the fat cell.
The above facts are crucial to lifelong weight management. People who don’t eat or eat too little increase the percentage of fat stored in their bodies. Consider this: anorexics who weigh 80 to 90 pounds can have as much as 40 percent to 50 percent body fat. Eventually they die because their hearts and liver “shrivel” up. Many of us have been taught that not eating will make us slim, but in truth, if you do not eat, your muscle mass will decrease and you will actually become fatter.
Here's the biochemistry behind muscle breakdown. Similar to low calorie diets, fasting (twelve to sixteen hours without eating) forces the body to switch to a wasting metabolism; i.e., exhausting carbohydrate reserves, and drawing on vital protein tissues. In the first few days of a fast or a low calorie diet, body protein provides about 90 percent of the needed glucose. If body proteins were to continue to be utilized at this rate, death would ensue within three weeks. However, as the low calorie diet or fast continues, the body finds a way to use fat by-products as a fuel source for some types of cells. Fats are broken down to produce by-products that look similar to glucose—ketones. Ketones can be used by some muscle cells, but other cells, such as brain cells, red blood cells, cells involved in vision can not use ketones and still rely on glucose. The only way the body can make glucose is to break down muscle cells (which are made up of proteins, which in turn are made of amino acids) and produce glucose from amino acids; hence, body proteins continue to be broken down. This is a dangerous process, since ketones can cause a disease state known as acidosis—changes in pH which can eventually cause death.
Fasting reduces energy output and the body conserves both its fat and lean tissue. As the lean organ tissues shrink, they perform less metabolic work and so demand less energy.
Bottom line:
