Look at the nutrition label and you'll see you're mistaken. Calories measure the energy in the product (the label shows kilocalories actually - Cal, not cal). Overpriced soda with extra caffeine and other stimulants have lots of calories. Not a healthy source of calories, but its got plenty of energy (1 Cal = 4184 J).
Brilliant. You could market heavy water as a healthy energy drink with the most energy but your nutrition label would still show zero calories. I don't think too many people could afford it, but rogue states would love it