[ceejayoz]

> There are calories in diamonds

Not in this context. A nutrition label for a 50 pound diamond would indicate zero calories.

[chrisseaton]

But again... that's the point. Everyone already knew 'a calorie is a calorie' was not literally true - for example diamonds which you agree about.

[ceejayoz]

People who say “a calorie is a calorie” clearly mean “calories from fats, carbs, and protein are interchangeable”, not “you can survive on a diet of diamonds”.