Kevin Hall gave a talk today on some of his recent results that forces me to revise what I wrote yesterday. I won’t divulge his exact results since it’s not published yet but he has experimental evidence that a calorie is not a calorie. What I said in my previous post was that if you are in steady state then it doesn’t matter what diet you are eating. However, that must be qualified in light of the recent data. To be in steady state, you must be in both energy and macronutrient balance. This means that you need to burn exactly all the food you eat, both in the caloric content and composition. What your body burns depends on the food you eat as well as your current body composition. So let’s say you decide to cut the carbs from your diet but eat the same amount of calories everyday. Your body must now burn all the extra fat you are eating to stay in steady state. If it can adjust immediately then you will stay in steady state. However, if it cannot burn all the extra fat you are eating then that excess fat will be stored and the body will burn extra glycogen or protein instead. Your body composition will then change until you are back in steady state. If your body over adjusts and you burn too much fat, then you will lose fat and gain lean tissue. In hindsight, the assumption that you can immediately adjust to whatever fuel you are taking in seems pretty far-fetched and according to Kevin’s data, it is.