Or maybe because that view is overly simplistic - to quote the article: We've long thought of weight loss in simple "calories in, calories out" terms. In a muc

Or maybe because that view is overly simplistic - to quote the article: We've long thought of weight loss in simple "calories in, calories out" terms. In a much-cited 1958 study, researcher Max Wishnofsky outlined a rule that many organizations — from the Mayo Clinic to Livestrong — still use to predict weight loss: A pound of human fat represents about 3,500 calories; therefore cutting 500 calories per day, through diet or physical activity, results in about a pound of weight loss per week. Similarly, adding 500 calories a day results in a weight gain of about the same. Today, researchers view this rule as overly simplistic. They now think of human energy balance as "a dynamic and adaptable system," as one study describes. When you alter one component — cutting the number of calories you eat in a day to lose weight, doing more exercise than usual — this sets off a cascade of changes in the body that affect how many calories you use up, and in turn, your body weight.