Apparently the US Calorie is because that formal definition was originally 1kg of water, it came to the US and got embedded in nutrition stuff, then got changed

Apparently the US Calorie is because that formal definition was originally 1kg of water, it came to the US and got embedded in nutrition stuff, then got changed to 1g of water: https://pubmed.ncbi.nlm.nih.gov/17116702/ https://pubmed.ncbi.nlm.nih.gov/17116702/