How many calories in a pint of blood?

I see Instapundit is encouraging people to give blood. He mentions that "the blood folks are always calling me saying they’re desperately short of blood, I wonder if the standards are too strict." The blood folks. Not everyone is purely altruistic! How many calories in a pint of blood? "Can I donate blood to lose weight?"

"Perhaps blood donation could be promoted as one way to lose a bit of unwanted weight. Taking into account the composition and energy in each component . . . I estimated that one unit of blood reflects about 600 cal of food intake. Hence, a single donation can off-set either 2 hamburgers, 3 donuts, or 5 granola bars. Awareness of these statistics might increase the appeal of blood donation, particularly among healthy adults who are concerned about obesity."