Of course bodies and metabolic rates behave differently in different contexts. That’s not a new discovery, it has been known for a long time. The new research i

Of course bodies and metabolic rates behave differently in different contexts. That’s not a new discovery, it has been known for a long time. The new research is just confirming what was known, and uncovering some of the specific mechanisms. How much differently? What contexts? What is the distribution of different metabolic behaviors? What is the range of different rates? Those questions are far more important than whether, if you actually want to understand how calories behave. The reasoning behind the phrase “a calorie is a calorie” is to summarize the primary metric one should watch when trying to lose weight. It doesn’t say that all calories are the same. You might have already noticed that the words are a tautology. A calorie literally is a calorie, it’s not saying that all calories are the same for all people in all contexts. An important question to ask here is what action should someone take, armed with the knowledge that metabolic rates have some variability? Does that mean you should not use calories? Do we have a better metric? I’m not aware of one, so believing that variability means you shouldn’t use calories as a metric would be the wrong conclusion, IMO. Calories have always been imperfect estimates, but we have no better estimate. Eating & drinking is the only way we add mass to our bodies, so calories merely attempt to quantify that mass. Knowing that metabolic rates have variability means only that someone who believes their rate to be very different from the average should work to calibrate their measurements. That takes effort and is difficult to do on top of an already difficult activity of monitoring and/or restricting calories, so I wouldn’t recommend trying to calibrate calorie measurements to someone who’s struggling to track calories. The estimates we have aren’t that bad, and they will work for the average person.