To find your resting metabolic rate multiply your body weight by 10. This number is roughly the minimum number of calories your body requires to lose weight.
Example: A 145 pound woman’s resting metabolic rate is roughly 1450 calories (if she’s sitting on the sofa all day). Then factor in daily activities and exercise and she will probably have 2000 calories to burn a day. So 1450 calories would be her minimum and 2000 her maximum.
Consuming fewer calories than your minimum causes your body to choose between burning fat or burning muscle. There is a point where cutting calories works against you by throwing your body into lock down (slower metabolism) to prevent you from starving. It will choose to lose the calorie consuming muscle and keep the slower calorie burning fat. Excessive loss of lean muscle mass leads to weight loss without improvement of body composition or health. And thus leads to frustration and the seemingly never ending battle with your weight.
A weight-loss program that is overly restrictive on calories will set you up for failure – and turn your 747 into a Volkswagen.