Based on fat-free mass, the number of calories your body uses each day, not counting the extra calories burned during exercise.
BMR is the minimum number of calories used by the body to stay alive with the mass that it is currently carrying. Sometimes diet programs will have a patient eat FAR less than the patient’s BMR with the hopes that this will make the patient loose weight. This often results in dramatic weight loss which may seem fine for patients, however, this is a slippery slope since most of the weight lost is muscle and very little fat. When this occurs, weight loss results in a lower body metabolism since muscle burns more calories at rest compared to fat. Patients who exhibit increase muscle loss move towards a sarcopenic state increasing the propensity to gain weight (in fat) in the future. This is why so many “fad” or “calorie restricted” diets do not work. Patients loose a lot of weight and then after a short period of time they gain even more weight back making it harder to loose each time. This may happen over and over again which is where the term “yo-yo dieter” comes from. Each time the weight drops more fat is eventually gained and less muscle is present making even harder to loose weight.