Generally, my claim is true.

Lumifer stated my opinion on why people don't lose weight pretty well: "the real reason is that [people are] unwilling to pay the various costs of losing weight."

It's difficult to achieve in many cases (dieting isn't fun), but we should be happy the formula for weight loss is pretty simple. People just choose not to do the things necessary.

More importantly it's irrelevant to the empirical fact that the success of the intervention of having people attempt to diet and exercise is mediocre. It's rational to chose interventions that work for other people.

I think there are some life hacky ways to approach fitness and weight loss. I, for instance, have very low will power. I'm lousy at moderation. My solution is to, as a zero tolerance policy, not eat certain foods. I also have a policy of working out 5 times a week, with no exceptions. I've used commitment contracts from time to time to aid me.

These are pretty simple measures. And all they do is allow me to (1) eat less and (2) exercise more. People just don't wanna.

Not every kind of calorie burn is due to exercise.

Your example is just a play on the word "exercise". Shopping is exercise. Walking, moving.

Your statement is trivially true in regard to metabolism, however. ~65% of basal metabolic rate (or resting metabolic rate) is, IIRC, based on the amount of lean muscle an individual has. In this way, it seems the fit will find it easier to stay fit and those with small amounts of lean muscle will always be fighting an uphill battle.

It's rational to chose interventions that work for other people.

I think the way LW talks about diet and weight loss is among the most irrational I've seen. It's not nearly as complicated as it's made out to be here. I'd imagine it's discouraging to many people.

You could create a weight loss book from all the knowledge and insight offered in the history of LW and it would be less valuable, in terms of its instrumental rationality to dieters, than a fortune cookie slip that said "Eat less, exercise more".