"A calorie is a calorie" is wrong, sure, but so is Newtonian physics. It leads to a lot of better-than-random-guessing predictions about what you should do in o

"A calorie is a calorie" is wrong, sure, but so is Newtonian physics. It leads to a lot of better-than-random-guessing predictions about what you should do in order to achieve certain goals. Want to gain weight? A gallon of milk is roughly 2k calories, so if you add that to your daily diet you ought to put on weight. Want to lose weight? You should probably "eat less", and calories are a good approximation of how much "less" eating less is.