why do you lose calories when donating blood?
In: Biology
Your body has to do work to regenerate the lost blood and plasma. Doing work burns calories.
You’ll lose a bit of stored energy that was in the blood.
More important, you’ll need to spend energy to make more blood.
And then a little bit more to heal the skin.
it’s not necessarily just “loosing calories”. Donating can cause your blood sugar levels to drop. So they’re giving you sugar in the form of juice or cookies to help prevent it from dropping too low. Juice also gives you the extra benefit of getting more fluid back into you, to help replenish some that you lost.
It quite literally removes tissue from your body, and replenishing that tissue requires energy
Humans, like all other animals are made of food. When you donate blood you give about 500mL of whole blood. Blood is about 40% red blood cells (RBCs) or roughly 200g of RBCs. RBCs are about 50% protein and 40% lipids so 100g protein, 80g lipids. Protein has 4 calories per gram and lipids 9. This adds up to 400cal of protein and 720cal of lipids for a total of 1,120 calories being physically removed from your body.
Platelets and white blood cells will be in there too, along with some glucose and other goodies, but in very small amounts. All the numbers are rough approximations.
I’ve never heard someone phrase it that way. I supposed you’d lose some blood sugar, energy that’s in the blood, as they take blood out of you. I think the bigger consideration is you were effectively wounded. Your body now has lots of work to do to get back to normal. Work takes energy, energy comes from food. So eating after donating blood gives your body fuel to get to work. Water has to be moved, basically pumped, back into veins if you lost blood volume. Bone marrow needs to make new cells. If blood cells are the product, bone marrow is like the factory and food the fuel to fire up the factory.
Maybe the trick is blood sugar. When you lose blood more fluid gets moved into the veins, restoring your blood volume but reducing the concentration of nutrients. So eating then helps restore blood sugar and nutrient levels back up to normal.
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