Science Questions

How many calories do you need to replace a pint of blood?

Sun, 9th Nov 2008

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John Chapman asked:

How many calories do you need to replace the tissue lost when you give a pint of blood away?


We put this to Professor Adrian Newland:

Adrian - About 650 calories, which Iím reliably informed is 3 Mars bars.

Chris - Why would it take energy to replace blood?

Adrian - Anything that develops tissue requires energy.

Chris - So what youíre saying is you just need to put the energy back in.


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John Chapman asked the Naked Scientists: My question is about becoming a blood donor as an aid to losing weight. Making body tissue uses a lot of energy (which is why, when young teenage boys hit a growth spurt, they often eat ravenously yet become slimmer while at the same time gaining height). I once read in pro-vegetarian literature that every kilo of food meat requires the consumption of 10 kilos of plant material to create it. Around a 10:1 reduction of energy to create tissue. So can you tell me roughly how many calories it would take to replace a pint of blood? Could you please quantify this in terms that every dieter can understand, such as the number of Mars Bars or portions of chips that is cancelled out by replacing a pint of blood every 16 weeks. Many thanks, John What do you think? John Chapman, Wed, 5th Nov 2008

The limiting factor for a vegetarian would probably be the iron. Bored chemist, Wed, 5th Nov 2008

According to the Mayo Clinic...

650 calories is almost three Mars bars.

Blood donation is one pint every three or four months.
So if the 650 calorie figure is correct, by becoming a blood donor you can eat about ten extra ten Mars bars per year,
(=> 1/5th of a Mars bar per week).
RD, Wed, 5th Nov 2008

Is the 650 calories burnt or lost, or is it that it takes 650 calories to replace the pint of blood or does the blood taken = 650 calories in value?

Its a confusing and maybe misleading statement by the Mayoclinic as it seems odd that you can burn calories just by donating blood. I now wonder about the ethics in the statement. Is it a way to increase blood donating maybe? by making people believe that by giving blood you would burn calories and thus lose weight.

However, by donating a pint you will lose somewhere around 570g in weight but the blood lost gets replaced quickly.

Personally, I think reducing the calorie intake would be a better way to lose calories and that donating blood to do so is a drastic measure. that mad man, Wed, 5th Nov 2008

You could always buy some leeches or get a tap fitted.
What about anaemia, though? lyner, Wed, 5th Nov 2008

If you started giving blood regularly and didn't increase your calorie intake to balance it, you would lose weight (not just the water).
Where's the ethical problem? Bored chemist, Thu, 6th Nov 2008

The ethical issue is in telling people an incomplete story. People want to lose weight and might not be aware of the dangers associated with too much blood loss.
It's difficult to over-donate in the UK but, elsewhere, it could be just another way for gullible people to self harm. lyner, Fri, 7th Nov 2008

Thanks sophiecentaur, you seem to understand what I was on about and replied better than I could.

One thing I'm not sure about is if these people who donate also get paid for donating?

Unfortunately I cant find a calorific value for human blood but pigs blood has a calorific value of around 350 calories per pint and is mostly made up of water. That is a very small amount and is equal to around 4 slices of bread, so the sums are also wrong.

Just found this:

I was not far off! that mad man, Sun, 9th Nov 2008

There are two factors to consider whole blood or plasma donation? In the united states you can only donate whole blood once every 56 days due to the time your body needs to replace the red blood cells. I think that would be the type that is approx 650 calories to replace. Plasma would be significantly less I think due to the fact that its mainly comprised of water, platelets, and nutrients. Anyways the Gatorade they give you usually with the donation should cover the initial caloric loss. croltz, Sun, 1st Apr 2012

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