Let's just pretend it's accurate and say your body burns 2000 kcal a day. If you have less glucose in your blood overall after giving blood, even if the ratio s

Let's just pretend it's accurate and say your body burns 2000 kcal a day. If you have less glucose in your blood overall after giving blood, even if the ratio should theoretically remain the same, your body is still going to burn 2000 kcal anyway, and maybe the blood glucose equilibrium reaches a lower level.