Most fitness conscious people know that there are 3500 calories in a pound of fat, theoretically, if you create a deficit of 3500 calories in a week, you lose a pound of fat.
Like most things in life, it isn't quite that simple. First, this assumes that all the weight lost will be fat. We know that inevitably when we lose weight, some of that loss is lean body mass along with the body fat.
Our bodies are constantly striving to maintain a balance. So although the amount of body fat lost is based on initial body fat level and the size of the calorie deficit, lean people tend to lose more lean body mass and retain more fat; fat people tend to lose more body fat and retain more lean tissue. This explains why obese people can tolerate aggressive low calorie diets better than already lean people. For those wishing to lose a moderate amount of body fat from a body which is not excessively fat, a gentler more conservative approach to dieting can be more successful, especially if the goal is to retain or improve muscle mass.
While a pound of fat metabolizes into about 3500 calories, a pound of muscle yields only about 600 calories. So if you create a weekly calorie deficit of 3500 calories, and you manage to lose nothing but body fat, you will lose one pound in weight. But if you lost instead 100% muscle, you would lose almost six pounds in weight. And the mirror will not love you!
