If youve ever tried to lose weight, you know the formula: 3,500 calories equal one pound. But a new analysis says the math isnt quite that simple, which is why many dieters get disappointed and give up. While the 3,500-calorie number, derived from measuring the energy content of weight lost, is technically correct, in practice that formula fails to account for dynamic responses in human metabolism to changes in diet and body composition. In actuality, researchers report, a given diet results in an uncertain degree of energy deficit. If cutting 500 calories a day really meant losing a pound a week, they point out, at that rate a 300-pound dieter would simply disappear in six years.
When people cut calories below the energy needed to maintain their current weight, that baseline begins to change, too, as pounds come off. At some point, weight loss may cease even at the lower calorie intake.
The scientists developed an altermate model of calorie intake and weight loss that better reflects metabolic changes and the bodys feedback mechanisms. Its more accurate, they concluded, to say that cutting 500 daily calories would result in a 50-pound weight loss over three or more years-and then only if a dieter really sticks to it.
TO LEARN MORE: The Lancet, August 27, 2011; abstract at dx.doi.org/10.1016/S0140-6736(11)60812-X.