Once you accept that diets don’t work (ie scientific fact)

It's probably because of this. It causes a lot of confusion and tbh I don't think we should keep saying it. A diet as in calorie restriction absolutely works. The problem is people are highly likely to go back to eating what they did before the restriction and gain the weight back. Of course this doesn't mean that the diet didn't work.

When we say 'diets don't work' we mean that they're hard and it's unlikely someone will stick with it. Which is true. But people interpret it as us saying 'there's no point dieting because it won't be effective' and so get defensive.

I honestly think we need to drop the 'diets don't work' mantra.