Uh... what are you talking about? Yeah, of course the inaccuracy of calories isn't important to the 90% whom... aren't counting calories or aren't dieting. Why you thought this was a valid point to make escapes me.

10 percent is not trivial if someone is trying to lose weight by counting calories while eating foods that are obesogenic. And yes, many people do this specifically because body fat comes down to a simple equation. Practically everyone I know whom has taken the calorie-counting approach has done so with the idea that they can still eat pasta and other crap. It's extremely common. Also, given that the calorie counts on packaged food can be off by as much as 20%, and that people at home are getting their TDEE from either calculators or fitness watches that estimate their TDEE, people doing CICO are at high risk for overeating and not losing body fat at a satisfactory rate. Moreover, if they're eating crap, they may be losing more weight in muscle than desired because the human body does not care about thermodynamics.

Yes, if a meal contains 150-300 "calories" than is suggested then that's a setback, especially for those using CICO as a way to give themselves permission to keep eating obesogenic crap. Someone can drive a car while stepping on both the gas and the brakes at the same time... buy why? Unless a person is weighing their food, calories are an imperfect measure that only measure one thing, which is heat. Calories tell you nothing about how metabolized substrates are being delegated. Is it being used immediately, or stored in glycogen, or stored in fat, or pooped out? Who knows! Calories will never tell you that.

For the sake of argument, let's pretend that we're trying to lose weight by eating no more than our BMR of 1650 calories per day and doing some exercise to put us into what some would call a "calorie deficit."

If we divide 1650 calories into 3 meals, each meal would be around 550 calories. However, in the worst case that the calorie estimate for these meals is off by 20%, then each meal contains 110 extra calories, putting our calorie intake 330 calories over our target.

Ok, that's fine. We'll just run those calories off at the gym, right? If we use a MET calculator, this would reveal that we'd have to run for around 35 minutes to actually oxidize enough food to produce 330 calories of heat. But what has actually happened here? Since glucose metabolism is prioritized, a significant amount of those calories won't have been produced by fat oxidation. If the food we're eating put our RQ at 1.0 or greater, such as if we're eating pasta and toquitoes, that puts us at greater risk of burning carbs but not fat. This isn't a bad thing per se, since some of those carbs might have been otherwise stored as fat. But after 35 minutes of intense running, how much have we really achieved if we are trying to lose body fat? Not much unless we run much longer than 35 minutes every day. Most people simply don't keep up this kind of routine for very long.

On the other hand, perhaps we end up undereating, or we decide to eat even less than we were before. This can work because something's gotta give and fat mass will continually be accessed and used. However, we would likely be at risk for muscle loss. Without enough protein, muscle is difficult to hold on to. If we reach a point where our glycogen stores are chronically exhausted, then glucose has to come from somewhere, and if it's satisfied by exogenous carbohydrates then it's gotta come from breaking down muscle through gluconeogenesis. We'll lose weight in the long run, but at what cost? Even if protein is factored in to meals, it still may not be enough if we're not eating as many calories as we thought we were.

If you think what I'm saying is trivial, then tell that to all the researchers you seem to think are wasting their time using calorimeters and metabolic carts.

Some of us, rather than counting calories in perpetuity, choose non-obesogenic diets that make it extremely difficult to overeat but are satisfying and provide enough nutrients to maintain and build lean mass. Just because someone can count calories and lose weight doesn't mean that someone who doesn't count calories and consumes more "calories" than their TDEE will necessarily gain body fat.

Again, nobody is saying that people can't lose weight counting calories. The issue is that it doesn't work well for everyone and there are alternatives that work in spite of it. It's only useful in the context that it leads you to undereating such that you're losing more mass than you're taking in, which may or may not actually happen.