The purpose of "a calorie is a calorie" is not to be scientific truth; it is to serve as guidance for people who are trying to lose weight and are falling prey

The purpose of "a calorie is a calorie" is not to be scientific truth; it is to serve as guidance for people who are trying to lose weight and are falling prey to particular mistakes. It's like if you're at the gym and a coach is telling someone "sit your butt back, butt back, butt back!" "Sit your butt back" isn't a universal directive for that exercise, much less everything you need to know about it. It's a correction for what that person is currently doing wrong. Six months from now, they might be sitting too far back, and the coach will say, "Don't let your butt go back!" Or the advice to, "Loosen up; people like it when you just say what's on your mind," versus, "You need to activate the filter between your brain and your mouth." These statements can both be true when directed at the right person in the right context. The paper takes aim at "a calorie is a calorie" as an objective scientific truth, which makes it trivially wrong, but doesn't address its pragmatic truth as advice. "A calorie is a calorie" is "true" when it is a good corrective for the person it's directed at. It's "false" if the person needs to be paying more attention to the differences, like if you're an athlete trying to fine-tune your diet for performance, or if you somehow never got the message that people need vegetables in their diet. It might be less true on HN, but in my experience with my family and acquaintances, "a calorie is a calorie" is a widely needed truth. Most people's approach to healthy eating is to sort foods into "good" and "bad" and try to minimize the harm from the "bad" foods, ignoring any potential for harm from the "good" foods. Some people give themselves a pass on the calories from olive oil and avocados because it's a "healthy fat." Other people focus on their intake of cheap processed corporate foods while not worrying about the generous quantities of expensive, local, artisanal bread and cheese and fancy meats they consume. There are even people in my generation who missed the whole last thirty years of carb controversy and mound up huge portions of spaghetti and garlic bread next to a 4oz cut of steak and call that a healthy meal because the only problematic food on the plate is in a tiny portion. For whatever reason, whether it's because of how nutritional information is presented to the public by experts or because of exploitative marketing from the diet industry or because our brains are wired to see good and bad everywhere, that's how an unfortunately very large number of people approach eating for weight loss, and "a calorie is a calorie" is a good corrective for them, to remind them to pay attention to the quantity of everything they eat, not just the "bad" stuff.