Re: Calories to produce pint of blood?

Hello, Craig.
Why is it you think that "the human body is not 100% efficient" in making 
blood?  The key is that we are talking about a HEALTHY human body.  Just 
ponder some of these marvels.
In just one second, 8 million blood cells die every second of our lives, 
but the same number is born in that time.  The bone marrow produces over 
200 billion red blood cells a day.  Your red blood cells travel some 950 
miles in 4 months.  More than half a ton of red blood cells are created in 
an average lifetime.  You contain some 25 to 30 trillion red blood cells 
and 75 billion white blood cells.  At the same time platelets are produced 
some 200 billion each day.  All this travelling through about 62,000 miles 
of arteries, veins and capillaries, feeding and servicing the rest of the 
body's 60 trillion cells!  Does this sound like an inefficient blood 
making machine to you?  Sure, there are plenty of diseases in which there 
can be an underproduction or even overproduction of blood.  Only in such 
circumstances is the body less than 100% efficient in blood making. (1.)
Food provides us with energy.  When we eat food, the cells take from it 
the components it needs to function and survive.  All cells need to be 
nourished, including muscle cells, nerve cells and of course, blood 
cells.  The various types of cells have different roles, but they do not 
act in isolation, rather, the trillions of cells that make up our body 
perform in concert as a unified and organized system.  The point is, that 
you cannot extract an involuntary function, such as the manufacture of 
blood, and place a caloric requirement to it.  These functions are 
interrelated and cannot be measured seperately.  As well, confounding 
factors exist, such as, age, body size, weight, gender, metabolic 
differences, physiological state and activity, environmental factors and 
even stress levels.  All of these factors would make a caloric prediction 
highly inaccurate, if not impossible.  
However, what we can do is to determine the least amount of energy 
required for the involuntary work of the body in order to maintain life, 
including respiration, maintenance of muscle tone, body temperature and 
circulation.  We call this the B.M.R. or basal metabolic rate.  It ranges 
from 1200 to 1400 kcals. for healthy women and 1600 to 1800 kcals. for 
healthy men.  (2.)
Calories from food can easily be determined, including food such as 
blood.  (See my answer for calories on: www.madsci.org, using their search 
engine, type keywords: "measure calories nut", and click exact words or 
exact phrase).  Blood has a long history as a food source for many 
societies, (other than for vampires, of course).  Today, the Masai tribe, 
who live in Tanzania, Africa, regularly drink blood as part of their diet. 
(3.)
The main benefit they derive from this practice is the protein content, 
coming from the iron rich protein called hemoglobin and the numerous 
proteins found in white bllod cells, such as albumin and globulins, as 
well as smaller proteins like platelets.  Approximately 22% of blood is 
solids, so, factoring in the remaining carbohydrates and fat, 1 pint of 
blood would yield the Masai about 400 kcals.
As you noted the caloric content of blood has been calculated and is 
available on the MadSci.org archives, which in my opinion was expertly 
answered by Dr. Mark Fung.)
Finally, you don't have to be concerned about eating a certain number of 
calories to replenish a pint of blood after a donation.  Within an hour or 
so, the blood volume has been replaced from fluid stores elsewhere in the 
body.  Within a few weeks the body has replaced the other parts of the 
blood and you're as good as new!
Hope that helps,
Peter Bosani.

References: 1. The Body Almanac - Neil McAleer.  Publisher - Doubleday
            2. Recommended Nutrient Intakes for Canadians.  Health & 
Welfare Canada.
            3. Food In History - Tannahill.  Publisher - Crown Publishers.
            4. Common Sense Medicine - Curtis H. Baylor M.D.  Publishers- 
Gramercy Publishing Co.