When introducing 3500, 4000 or 5000 calories every day, or cutting calories down to 1500, 1200 or 1000 calories per day, you disrupt the normal mechanism that should work within an allowed limit.
How the weight keeping mechanism works:
There are many "set points" of different measures of the body that either genetically coded (like body temperature), or dictated by the surrounding environment (like stress). These set points are present in a part of our brain called Hypothalamus. One of the major functions of the hypothalamus is to regulate secretion of endocrine hormones directly into the blood. Hormones and nerves form the 2 regulatory mechanisms of the body.
The hypothalamus also sets a point for body weight based on the level of the input and output of calories it is used to. It seeks to keep the body weight constant, even if this point is over what it should be ( like in obese children). This is achieved through storing calories or burning calories, i.e. it either directs the body to utilize external glucose, or to build glucose from other internal resources.
How do you disrupt the "set point" of your weight:
Normally, if you are over 30 and keeping on the same level of calorie intake you are used to, the hormonal balance at this age favors storing a bit more calories in the form of fat.
If you are over 30 and introduce more calories than your basal metabolism needs (2900 in males and 2200 in females), with less physical activity the extra calories are stored as fats, cumulatively, a new set point is created at which response to insulin (that helps burn glucose) is no more the same way as before, a case known as insulin insensitivity.
As overweight is a big phenomenon, so it should create a marketing opportunity with different products, among these products are the diet plans, and to offer a new advantage many diet plans have created a buzz about the period of time through which you lose weight, the shorter the time the better is the product.
We see 1500 calories, 1200 calories, and even 1000 calories/day diet plans. Extremely low-calorie diets may help you shed pounds quickly, but they will lead to failure in the long run. We are genetically protected against starvation! During food storage, our bodies slow down our metabolism and burns less energy so we can stay alive.
When we drastically cut back our food intake, the brain thinks the body is starving and in an effort to preserve life it slows down the metabolism. Soon the pounds stop coming off in the plateau stage, As a result we grow hungry and uncomfortable and then eat more and return back to a worse situation.
All you need to change your metabolic rate is to change the nutritional composition of the foods you eat. If you are overweight, all you need is to cut down on total calories to be 2000-calories/day, a little below your basal metabolic rate to urge the body to burn some fats.
Avoid starvation panic in your system, just keep your calorie intake to be within 2000-calories by eating nutrient-rich plant foods, this will convince your brain that your body is getting all the nutrients it needs.
Plant foods move slowly in your gut making you feel full longer, and they are rich in vitamins,minerals,trace elements and anti-oxidants. you earn an extra bonus in the form of negative calorie effect.
The base line is that when you want to lose weight, you do not have to make your body obeys the conventional wisdom laws, rather try to understand your natural body laws and obey them. Cut on your total calorie intake to 2000-calories/day and avoid starvation panic in your system, your body did not get extra weight over 1,2... or even 30 nights, so why would you make it lose them over 2 or 3 weeks?!
You like eating? Deceive your body and increase number of meals or snacks, and fill your stomach with full, nutritive, healthy foods within 2000-calories, and stop fighting your body.