On some level, calories in calories out has to be true. But these variables are not independent. Bodies respond to exercise by getting hungry and to calorie deficit by getting tired. Even absent that, bodies know how much food they want, and if you don’t give it to them they will tell you at increasing volume until you give in (not all bodies, of course, but quiet stomachs aren’t the target market for GLP-1s). A new breed of drugs, GLP-1 agonists, offer a way out of the latter trap by telling yo...