Re: How many calories does the body use in donating blood?

Aloha,

     Since I just got back from donating blood myself at one of our campus 
blood drives at the University of Hawai`i, it seems the appropriate time 
to answer your interesting question. I am a nutrition sciences faculty 
member here at UHM...and your question could have come from one of my 
introductory nutrition students.
     In a normal donation, you give/lose a pint of blood (and a little bit 
extra for the small tubes to test for safety concerns, like HIV, and 
finger-stick and to test for your iron status, to make sure that donating 
won't put you at risk for iron-deficiency anemia).  That pint of blood is 
mostly water, so you 'lose' (temporarily) about a pound (16 ounces in a 
pint).
     You also lose a bit of all the wide variety of cells and dissolved 
substances in your blood...minerals, vitamins, glucose, amino acids, fatty 
substances, hormones, etc.  The actual act of donation 'costs' you 
virtually nothing in energy expended, since you don't do anything except 
lie there and let the blood drive person extract the pint/plus.  One of 
the main 'energy sources' that you will lose is the glucose in your 
blood...let's assume that you have a blood glucose concentration of about 
100 mg/dL...that means in the 500 ml (5 dL) of blood (about a pint) that 
you donated, there would be about 500 mg glucose lost...Glucose provides 4 
kcal/g, so you lost about 2 kcal (less than the food energy in a stalk of 
celery). Even with the additional loss of amino acids and fatty 
substances, you lose virtually 'no' energy.
     The fact that you feel weak for some time after donating could be due 
to the water loss, initially.  With proper rehydration, that should be 
taken care of within a day.  So the message is to drink plenty of fluids 
before/after donating.  The other main reason that you are feeling tired 
could be that you may not have enough iron...and the loss of the iron in 
the pint of blood (in the red blood cell hemoglobin) might just put 
you 'over the edge' into a temporary problem.  My first suggestion is that 
you discuss with the blood drive person what your hemoglobin number is and 
what it means...to see if you are borderline with respect to blood iron. 
It takes longer for your body to rebuild the red blood cells lost through 
donation...about a week, I think. 
     The next, most obvious solution is that you make sure that you have 
adequate iron in your diet, BEFORE you donate again.  Good sources of iron 
are animal flesh (fish, meat, poultry), dried peas/beans, fortified grain 
products, and some vegetables...also, iron can be gotten as part of a 
vitamin/mineral tablet.  Iron in plant food and non-flesh animal food 
(eggs, milk) is also better absorbed when you get some vitamin C-
containing foods along with the iron-containing food...like orange juice, 
strawberries, some vegetables (broccoli, cauliflower, green peppers), and 
other fruits.
    I hope this answers your questions...and I hope that you and your 
friends continue to donate blood...it REALLY does make a difference.